Arrays of Fresnel Nanosystems for Enhanced Photovoltaic PerformanceClick to copy article linkArticle link copied!
- Ashish PrajapatiAshish PrajapatiSchool of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva 8410501, IsraelMore by Ashish Prajapati
- Gil Shalev*Gil Shalev*Email: [email protected]School of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva 8410501, IsraelThe Ilse-Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 8410501, IsraelMore by Gil Shalev
Abstract
Omnidirectional broadband absorption of the solar radiation is pivotal to solar energy harvesting and particularly to low-cost non-tracking photovoltaic (PV) technologies. The current work numerically examines the utilization of surface arrays composed of Fresnel nanosystems (Fresnel arrays), which are reminiscent of the known Fresnel lenses, for the realization of ultra-thin silicon PV cells. Specifically, the optical and electrical performances of PV cells integrated with Fresnel arrays are compared with those of a PV cell incorporated with an optimized surface array of nanopillars (NP array). It is shown that the broadband absorption of specifically tailored Fresnel arrays can provide an enhancement of ∼20% over that of an optimized NP array. The performed analysis suggests that broadband absorption in ultra-thin films decorated with Fresnel arrays is driven by two light trapping mechanisms. The first is light trapping governed by light concentration, induced by the arrays, into the underlying substrates, which increases the optical coupling between the impinging illumination and the substrates. The second mechanism is light trapping motivated by refraction, as the Fresnel arrays induce lateral irradiance in the underlying substrates, which increases the optical interaction length and hence the overall probability for optical absorption. Finally, PV cells incorporated with surface Fresnel arrays are numerically calculated, with short-circuit current densities (Jsc) which are ∼50% higher than that of a PV cell incorporated with an optimized NP array. Also, the effect of increased surface area, due to the presence of Fresnel arrays, and its effect on surface recombination and open-circuit voltage (Voc) are discussed.
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Introduction
Methods
Results and Discussion
Figure 1
Figure 1. (a) Illustrations of the various considered Fresnel complexes with the relevant geometrical parameters. (b) θ-dependency of the broadband absorption of the full complexes, the arrays, and the substrates for the various considered geometries. (c) θ-dependency of the broadband reflection and the broadband transmission for the concave complex, the convex complex, NP complex, and θ = 0° complex. (d) AOI-dependency of the θ = −35° and the θ = 15° arrays (both with tcircle = 30 nm). Note: the NP complex is also shown for reference.
Figure 2
Figure 2. (a) θ-dependency of the lateral and vertical irradiance for the full complexes, for the arrays, and for the substrates. The NP array is also shown for reference. The arrow next to E reflects the direction of the impinging irradiance electric field. (b) θ-dependency of the broadband absorption depth profiles for convex and concave arrays, both with tcircle = 30 nm. The NP array is also shown for reference. The x-axis zero value marks the top of the substrate. (c) Cross-sections showing the normalized APD under broadband illumination for θ = 0, 15, 35, and 55°.
Figure 3
Figure 3. (a) Illustrations showing the considered PV cells. (b) I–V curves under broadband illumination for selected θ values and an absorber doping concentration of 1017 cm–3. (c) Dependency of Jsc, Voc, and nPCE on absorber doping level for the selected θ values. (d) SRV-dependency of Jsc, Voc, and nPCE for the selected θ values.
Conclusions
References
This article references 40 other publications.
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- 3Yan, T.; Li, Z.; Cao, F.; Chen, J.; Wu, L.; Fang, X. An All-Organic Self-Powered Photodetector with Ultraflexible Dual-Polarity Output for Biosignal Detection. Adv. Mater. 2022, 34, 2201303, DOI: 10.1002/adma.202201303Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xhs12gtLbO&md5=0b9080c626c77c7c4cde2e7f5f770a6cAn All-Organic Self-Powered Photodetector with Ultraflexible Dual-Polarity Output for Biosignal DetectionYan, Tingting; Li, Ziqing; Cao, Fa; Chen, Jiaxin; Wu, Limin; Fang, XiaoshengAdvanced Materials (Weinheim, Germany) (2022), 34 (30), 2201303CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Endowing photodetectors with mech. flexibility and actual functionality are current research issues in developing optoelectronic devices. However, rigid metal-based or metal-oxide-based electrodes remain a block to the realization of ultraflexible electronics. Thus, an ultraflexible all-org. photodetector (all-OPD) is designed by innovatively introducing sym. org. electrodes PH1000/PH1000 to substitute the widely applied indium-doped tin oxide (ITO)/Ag electrodes. Specifically, this all-OPD exhibits a high self-powered responsivity (R) of over 100 mA W-1 among 500-600 nm and the photocurrent remains about 80% of the original performance after being bent 20 000 circles, and can output steady biosignals for photo-plethysmog. (PPG) application. More importantly, this all-OPD outputs dual-polarity photocurrent as it is flipped or folded. Benefitting from the ordered phase distribution and designed Schottky barrier heights, the photogenerated holes will be transferred and collected by nearer electrode, while electrons will be trapped in the thick bulk heterojunction (BHJ) as a result of the long channel. This work offers a new avenue toward developing a multifunctional and ultraflexible all-OPD with a straightforward all-soln. method, and it is expected to be more compatible in complex application scenarios.
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- 5Yu, Z.; Raman, A.; Fan, S. Fundamental Limit of Light Trapping in Grating Structures. Opt. Express 2010, 18, A366– A380, DOI: 10.1364/OE.18.00A366Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Skt7%252FL&md5=9a1bfbf29b02fbc51be2f0c104aa450fFundamental limit of light trapping in grating structuresYu, Zongfu; Raman, Aaswath; Fan, ShanhuiOptics Express (2010), 18 (S3), A366-A380CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n2, but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile's symmetry on the absorption enhancement limit. Numerical simulations are applied to support the theory. Our findings provide general guidance for the design of grating structures for light-trapping solar cells.
- 6Yu, Z.; Raman, A.; Fan, S. Fundamental Limit of Nanophotonic Light Trapping in Solar Cells. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 17491– 17496, DOI: 10.1073/pnas.1008296107Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlartbzM&md5=8a4a452e53ec41702c28a630d601efcaFundamental limit of nanophotonic light trapping in solar cellsYu, Zongfu; Raman, Aaswath; Fan, ShanhuiProceedings of the National Academy of Sciences of the United States of America (2010), 107 (41), 17491-17496, S17491/1-S17491/4CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Establishing the fundamental limit of nanophotonic light-trapping schemes is of paramount importance and is becoming increasingly urgent for current solar cell research. The std. theory of light trapping demonstrated that absorption enhancement in a medium cannot exceed a factor of 4n2/sin2θ, where n is the refractive index of the active layer, and θ is the angle of the emission cone in the medium surrounding the cell. This theory, however, is not applicable in the nanophotonic regime. Here we develop a statistical temporal coupled-mode theory of light trapping based on a rigorous electromagnetic approach. Our theory reveals that the conventional limit can be substantially surpassed when optical modes exhibit deep-subwavelength-scale field confinement, opening new avenues for highly efficient next-generation solar cells.
- 7Callahan, D. M.; Munday, J. N.; Atwater, H. a. Solar Cell Light Trapping beyond the Ray Optic Limit. Nano Lett. 2012, 12, 214– 218, DOI: 10.1021/nl203351kGoogle Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhs1Slsr%252FK&md5=01b05dea21d6bd5cb5a863896a480d98Solar Cell Light Trapping beyond the Ray Optic LimitCallahan, Dennis M.; Munday, Jeremy N.; Atwater, Harry A.Nano Letters (2012), 12 (1), 214-218CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Yablonovitch proposed a thermodn. limit on light trapping within homogeneous semiconductor slabs, which implied a min. thickness needed to fully absorb the solar spectrum. However, this limit is valid for geometrical optics but not for a new generation of sub-wavelength solar absorbers such as ultrathin or inhomogeneously structured cells, wire-based cells, photonic crystal-based cells and plasmonic cells. The key to exceeding the conventional ray optic or so-called ergodic light trapping limit is in designing an elevated local d. of optical states (LDOS) for the absorber. Also, for any semiconductor it is always possible to exceed the ray optic light trapping limit and use these principles to design a no. of new solar absorbers with the key feature of having an elevated LDOS within the absorbing region of the device, opening new avenues for solar cell design and cost redn.
- 8Sturmberg, B. C. P.; Dossou, K. B.; Botten, L. C.; Asatryan, A. A.; Poulton, C. G.; McPhedran, R. C.; de Sterke, C. M. Absorption Enhancing Proximity Effects in Aperiodic Nanowire Arrays. Opt. Express 2013, 21, A964– A969, DOI: 10.1364/OE.21.00A964Google ScholarThere is no corresponding record for this reference.
- 9Hu, L.; Chen, G. Analysis of Optical Absorption in Silicon Nanowire Arrays for Photovoltaic Applications. Nano Lett. 2007, 7, 3249– 3252, DOI: 10.1021/nl071018bGoogle Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFehu7fK&md5=afffda995213a968fb853a85827f4a54Analysis of Optical Absorption in Silicon Nanowire Arrays for Photovoltaic ApplicationsHu, Lu; Chen, GangNano Letters (2007), 7 (11), 3249-3252CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)An anal. of the optical absorption in Si nanowire arrays for application in solar cells is presented. The effects of wire diam., length, and filling ratio on the absorptance of nanowire arrays were simulated. Nanowire arrays with moderate filling ratios have a lower reflectance than thin films. At high frequencies nanowire arrays have higher absorptance than thin films. At low frequencies nanowire arrays absorb less but can be designed to approach that of the film by changing the filling ratio.
- 10Spinelli, P.; Verschuuren, M. A.; Polman, A. Broadband Omnidirectional Antireflection Coating Based on Subwavelength Surface Mie Resonators. Nat. Commun. 2012, 3, 692, DOI: 10.1038/ncomms1691Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC383lt12guw%253D%253D&md5=c9aa8663017049f503952f5a43f789bcBroadband omnidirectional antireflection coating based on subwavelength surface Mie resonatorsSpinelli P; Verschuuren M A; Polman ANature communications (2012), 3 (), 692 ISSN:.Reflection is a natural phenomenon that occurs when light passes the interface between materials with different refractive index. In many applications, such as solar cells or photodetectors, reflection is an unwanted loss process. Many ways to reduce reflection from a substrate have been investigated so far, including dielectric interference coatings, surface texturing, adiabatic index matching and scattering from plasmonic nanoparticles. Here we present an entirely new concept that suppresses the reflection of light from a silicon surface over a broad spectral range. A two-dimensional periodic array of subwavelength silicon nanocylinders designed to possess strongly substrate-coupled Mie resonances yields almost zero total reflectance over the entire spectral range from the ultraviolet to the near-infrared. This new antireflection concept relies on the strong forward scattering that occurs when a scattering structure is placed in close proximity to a high-index substrate with a high optical density of states.
- 11Kim, S. K.; Zhang, X.; Hill, D. J.; Song, K. D.; Park, J. S.; Park, H. G.; Cahoon, J. F. Doubling Absorption in Nanowire Solar Cells with Dielectric Shell Optical Antennas. Nano Lett. 2015, 15, 753– 758, DOI: 10.1021/nl504462eGoogle Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitFOku77M&md5=d09228b384cdba69fe2cd1f004f932b9Doubling Absorption in Nanowire Solar Cells with Dielectric Shell Optical AntennasKim, Sun-Kyung; Zhang, Xing; Hill, David J.; Song, Kyung-Deok; Park, Jin-Sung; Park, Hong-Gyu; Cahoon, James F.Nano Letters (2015), 15 (1), 753-758CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Semiconductor nanowires (NWs) often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indexes of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small vols. of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely det. the economic viability of NW-based solar cells. Here, the authors demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielec. shells. Scattering and absorption measurements on Si NWs coated with shells of SiNx or SiOx exhibit a broadband enhancement of light absorption by ∼50-200% and light scattering by ∼200-1000%. The increased light-matter interaction leads to a ∼ 80% increase in short-circuit c.d. in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the exptl. results and indicate the dielec.-shell effect to be a general phenomenon for groups IV, II-VI, and III-V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approx. double the efficiency of NW-based solar cells.
- 12Li, Y.; Li, M.; Fu, P.; Li, R.; Song, D.; Shen, C.; Zhao, Y. A Comparison of Light-Harvesting Performance of Silicon Nanocones and Nanowires for Radial-Junction Solar Cells. Sci. Rep. 2015, 5, 11532, DOI: 10.1038/srep11532Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFyhsbzO&md5=2a61e9cf7d6a2f47914107538f45504dA comparison of light-harvesting performance of silicon nanocones and nanowires for radial-junction solar cellsLi, Yingfeng; Li, Meicheng; Fu, Pengfei; Li, Ruike; Song, Dandan; Shen, Chao; Zhao, YanScientific Reports (2015), 5 (), 11532CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)Silicon nanorod based radial-junction solar cells are competitive alternatives to traditional planar silicon solar cells. In various silicon nanorods, nanocone is always considered to be better than nanowire in light-absorption. Nevertheless, we find that this notion isn't absolutely correct. Silicon nanocone is indeed significantly superior over nanowire in light-concn. due to its continuous diams., and thus resonant wavelengths excited. However, the concd. light can't be effectively absorbed and converted to photogenerated carriers, since its propagation path in silicon nanocone is shorter than that in nanowire. The results provide crit. clues for the design of silicon nanorod based radial-junction solar cells.
- 13Wong, A. B.; Brittman, S.; Yu, Y.; Dasgupta, N. P.; Yang, P. Core-Shell CdS-Cu2S Nanorod Array Solar Cells. Nano Lett. 2015, 15, 4096– 4101, DOI: 10.1021/acs.nanolett.5b01203Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXoslylsb0%253D&md5=2164fc119f727db3258135f71eb7c905Core-Shell CdS-Cu2S Nanorod Array Solar CellsWong, Andrew Barnabas; Brittman, Sarah; Yu, Yi; Dasgupta, Neil P.; Yang, PeidongNano Letters (2015), 15 (6), 4096-4101CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)As an earth-abundant p-type semiconductor, copper sulfide (Cu2S) is an attractive material for application in photovoltaic devices. However, it suffers from a minority carrier diffusion length that is less than the length required for complete light absorption. Core-shell nanowires and nanorods have the potential to alleviate this difficulty because they decouple the length scales of light absorption and charge collection. To achieve this geometry using Cu2S, cation exchange was applied to an array of CdS nanorods to produce well-defined CdS-Cu2S core-shell nanorods. Previous work demonstrated single-nanowire photovoltaic devices from this material system, but the cation exchange chem. was applied to nanorod arrays to produce ensemble-level devices with microscale sizes. The core-shell nanorod array devices show power conversion efficiencies of up to 3.8%. These devices are stable when measured in air after nearly one month of storage in a desiccator. These results are a 1st step in the development of large-area nanostructured Cu2S-based photovoltaics that can be processed from soln.
- 14Nowzari, A.; Heurlin, M.; Jain, V.; Storm, K.; Hosseinnia, A.; Anttu, N.; Borgström, M. T.; Pettersson, H.; Samuelson, L. A Comparative Study of Absorption in Vertically and Laterally Oriented InP Core-Shell Nanowire Photovoltaic Devices. Nano Lett. 2015, 15, 1809– 1814, DOI: 10.1021/nl504559gGoogle Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXisF2htbc%253D&md5=fdb9c6af3ce66f3d43973892652978bdA Comparative Study of Absorption in Vertically and Laterally Oriented InP Core-Shell Nanowire Photovoltaic DevicesNowzari, Ali; Heurlin, Magnus; Jain, Vishal; Storm, Kristian; Hosseinnia, Ali; Anttu, Nicklas; Borgstroem, Magnus T.; Pettersson, Haakan; Samuelson, LarsNano Letters (2015), 15 (3), 1809-1814CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The absorption in InP core-shell nanowire p-i-n junctions was compared in lateral and vertical orientation. Arrays of vertical core-shell nanowires with 400 nm pitch and 280 nm diam., as well as corresponding lateral single core-shell nanowires, were configured as photovoltaic devices. The photovoltaic characteristics of the samples, measured under 1 sun illumination, showed a higher absorption in lateral single nanowires compared to that in individual vertical nanowires, arranged in arrays with 400 nm pitch. Electromagnetic modeling of the structures confirmed the exptl. observations and showed that the absorption in a vertical nanowire in an array depends strongly on the array pitch. Depending on the array pitch, absorption in a vertical nanowire can be lower or higher than that in a lateral nanowire with equal absorption predicted at a pitch of 510 nm for the nanowire geometry. The described technol. facilitates quant. comparison of absorption in laterally and vertically oriented core-shell nanowire p-i-n junctions and can aid in the design, optimization, and performance evaluation of nanowire-based core-shell photovoltaic devices.
- 15Wallentin, J.; Anttu, N.; Asoli, D.; Huffman, M.; Aberg, I.; Magnusson, M. H.; Siefer, G.; Fuss-Kailuweit, P.; Dimroth, F.; Witzigmann, B.; Xu, H. Q.; Samuelson, L.; Deppert, K.; Borgström, M. T. InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit. Science 2013, 339, 1057– 1060, DOI: 10.1126/science.1230969Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjtVGjs7s%253D&md5=efdf6db71841214bb23468af37ef5558InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics LimitWallentin, Jesper; Anttu, Nicklas; Asoli, Damir; Huffman, Maria; Aaberg, Ingvar; Magnusson, Martin H.; Siefer, Gerald; Fuss-Kailuweit, Peter; Dimroth, Frank; Witzigmann, Bernd; Xu, H. Q.; Samuelson, Lars; Deppert, Knut; Borgstroem, Magnus T.Science (Washington, DC, United States) (2013), 339 (6123), 1057-1060CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Photovoltaics based on nanowire arrays could reduce cost and materials consumption compared with planar devices but have exhibited low efficiency of light absorption and carrier collection. We fabricated a variety of millimeter-sized arrays of p-type/intrinsic/n-type (p-i-n) doped InP nanowires and found that the nanowire diam. and the length of the top n-segment were crit. for cell performance. Efficiencies up to 13.8% (comparable to the record planar InP cell) were achieved by using resonant light trapping in 180-nm-diam. nanowires that only covered 12% of the surface. The share of sunlight converted into photocurrent (71%) was six times the limit in a simple ray optics description. Furthermore, the highest open-circuit voltage of 0.906 V exceeds that of its planar counterpart, despite about 30 times higher surface-to-vol. ratio of the nanowire cell.
- 16Aberg, I.; Vescovi, G.; Asoli, D.; Naseem, U.; Gilboy, J. P.; Sundvall, C.; Dahlgren, A.; Svensson, K. E.; Anttu, N.; Bjork, M. T. A GaAs Nanowire Array Solar Cell with 15.3 % Efficiency at 1 Sun. IEEE J. Photovoltaics 2016, 6, 185– 190, DOI: 10.1109/jphotov.2015.2484967Google ScholarThere is no corresponding record for this reference.
- 17Shalev, G.; Schmitt, S.; Brönstrup, G.; Christiansen, S. Maximizing the Ultimate Absorption Efficiency of Vertically-Aligned Semiconductor Nanowire Arrays with Wires of a Low Absorption Cross-Section. Nano Energy 2015, 12, 801– 809, DOI: 10.1016/j.nanoen.2015.01.048Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXivFWmt7o%253D&md5=1405cfe2b1a285c2995ded0fd96dd819Maximizing the ultimate absorption efficiency of vertically-aligned semiconductor nanowire arrays with wires of a low absorption cross-sectionShalev, Gil; Schmitt, Sebastian W.; Broenstrup, Gerald; Christiansen, SilkeNano Energy (2015), 12 (), 801-809CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Single semiconducting nanowires with sub-wavelength diams. exhibit superior light absorption, and hence triggered a vivid discussion regarding the application of these nanostructures into future generations of high efficiency solar cells. We examine the transition from a single highly absorbing silicon wire into an array composed of such individuals in order to validate the application of these into solar harvesting devices. We use finite-difference time-domain simulations to show that the coupling of the Fabry-Perot oscillations with the waveguide resonances inside the wires has a significant effect on the array absorption. For example, the ultimate absorption efficiency of a square-tiled wire array under normal incidence (array period of 0.5 μm, wire diam. of 0.4 μm and wire height of 2) is 81% higher than a 2 μm thin-film when the Fabry-Perot oscillations are considered and 37% higher when these oscillations are not considered. This coupling screens out the contribution of the waveguide modes to the array absorption and therefore, unlike previously published work, we eliminate the contribution of the Fabry-Perot oscillations. In this manner we demonstrate the absorption enhancement due to waveguide modes, and general correlations between the nanowire geometry and the overall array absorption are presented. First, we show that once an isolated wire with high absorption cross-section is nested inside an array its absorption decreases due to wire proximity effects. Secondly, the array absorption is maximized with relatively wide wires of low absorption cross-sections. We show that a 75 nm wire inside an square-tiled array with 2 μm period has an av. absorption efficiency factor of 6.5 and the av. relative absorption of the array is 0.5%, while the same wire nested inside an array of a 0.25 μm period exhibits 2.3 av. absorption efficiency factor and the array exhibits av. relative absorption of 9.85%. Finally, there is an optimized wire diam. that once exceeded the array absorption converges to that of a continuous film. For example, the max. absorption of 0.5 μm array is obtained with wire diam. of 0.4 μm where a decrease in relative absorption is recorded for arrays with wires exceeding 0.4 μm.
- 18Huang, Y.-F.; Chattopadhyay, S.; Jen, Y.-J.; Peng, C.-Y.; Liu, T.-A.; Hsu, Y.-K.; Pan, C.-L.; Lo, H.-C.; Hsu, C.-H.; Chang, Y.-H.; Lee, C.-S.; Chen, K.-H.; Chen, L.-C. Improved Broadband and Quasi-Omnidirectional Anti-Reflection Properties with Biomimetic Silicon Nanostructures. Nat. Nanotechnol. 2007, 2, 770– 774, DOI: 10.1038/nnano.2007.389Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtlyktL7F&md5=dcfb0c253b6fad4b8be25fdc19e1ad24Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructuresHuang, Yi-Fan; Chattopadhyay, Surojit; Jen, Yi-Jun; Peng, Cheng-Yu; Liu, Tze-An; Hsu, Yu-Kuei; Pan, Ci-Ling; Lo, Hung-Chun; Hsu, Chih-Hsun; Chang, Yuan-Huei; Lee, Chih-Shan; Chen, Kuei-Hsien; Chen, Li-ChyongNature Nanotechnology (2007), 2 (12), 770-774CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A simple aperiodic array of Si nanotips on a 6-in. wafer with a sub-wavelength structure can suppress the reflection of light at a range of wavelengths from the UV, through the visible part of the spectrum, to the THz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the Si result from changes in the refractive index caused by variations in the height of the Si nanotips, and can be simulated with models that were used to explain the low reflection from moth eyes. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electrooptical devices for the military.
- 19Jeong, S.; McGehee, M. D.; Cui, Y. All-Back-Contact Ultra-Thin Silicon Nanocone Solar Cells with 13.7% Power Conversion Efficiency. Nat. Commun. 2013, 4, 2950, DOI: 10.1038/ncomms3950Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c3ls12mtA%253D%253D&md5=9111dac4d851f142281b9f2a403a100bAll-back-contact ultra-thin silicon nanocone solar cells with 13.7% power conversion efficiencyJeong Sangmoo; McGehee Michael D; Cui YiNature communications (2013), 4 (), 2950 ISSN:.Thinner Si solar cells with higher efficiency can make a Si photovoltaic system a cost-effective energy solution, and nanostructuring has been suggested as a promising method to make thin Si an effective absorber. However, thin Si solar cells with nanostructures are not efficient because of severe Auger recombination and increased surface area, normally yielding <50% EQE with short-wavelength light. Here we demonstrate >80% EQEs at wavelengths from 400 to 800 nm in a sub-10-μm-thick Si solar cell, resulting in 13.7% power conversion efficiency. This significant improvement was achieved with an all-back-contact design preventing Auger recombination and with a nanocone structure having less surface area than any other nanostructures for solar cells. The device design principles presented here balance the photonic and electronic effects together and are an important step to realizing highly efficient, thin Si and other types of thin solar cells.
- 20Savin, H.; Repo, P.; von Gastrow, G.; Ortega, P.; Calle, E.; Garín, M.; Alcubilla, R. Black Silicon Solar Cells with Interdigitated Back-Contacts Achieve 22.1% Efficiency. Nat. Nanotechnol. 2015, 10, 624– 628, DOI: 10.1038/nnano.2015.89Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlOhu7rO&md5=a4074ebeb81334033a0dc2f6c6c7b132Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiencySavin, Hele; Repo, Paivikki; von Gastrow, Guillaume; Ortega, Pablo; Calle, Eric; Garin, Moises; Alcubilla, RamonNature Nanotechnology (2015), 10 (7), 624-628CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)The nanostructuring of silicon surfaces-known as black silicon-is a promising approach to eliminate front-surface reflection in photovoltaic devices without the need for a conventional antireflection coating. This might lead to both an increase in efficiency and a redn. in the manufg. costs of solar cells. However, all previous attempts to integrate black silicon into solar cells have resulted in cell efficiencies well below 20% due to the increased charge carrier recombination at the nanostructured surface. Here, we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing excellent chem. and elec. passivation. We demonstrate that efficiencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have real potential for industrial prodn. Furthermore, we show that the use of black silicon can result in a 3% increase in daily energy prodn. when compared with a ref. cell with the same efficiency, due to its better angular acceptance.
- 21Brongersma, M. L.; Cui, Y.; Fan, S. Light Management for Photovoltaics Using High-Index Nanostructures. Nat. Mater. 2014, 13, 451– 460, DOI: 10.1038/nmat3921Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmsFamur0%253D&md5=3879a9839d88793a0e13953f89ff9235Light management for photovoltaics using high-index nanostructuresBrongersma, Mark L.; Cui, Yi; Fan, ShanhuiNature Materials (2014), 13 (5), 451-460CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)A review. High-performance photovoltaic cells use semiconductors to convert sunlight into clean elec. power, and transparent dielecs. or conductive oxides as antireflection coatings. A common feature of these materials is their high refractive index. Whereas high-index materials in a planar form tend to produce a strong, undesired reflection of sunlight, high-index nanostructures afford new ways to manipulate light at a subwavelength scale. For example, nanoscale wires, particles and voids support strong optical resonances that can enhance and effectively control light absorption and scattering processes. As such, they provide ideal building blocks for novel, broadband antireflection coatings, light-trapping layers and super-absorbing films. This Review discusses some of the recent developments in the design and implementation of such photonic elements in thin-film photovoltaic cells.
- 22Garnett, E.; Yang, P. Light Trapping in Silicon Nanowire Solar Cells. Nano Lett. 2010, 10, 1082– 1087, DOI: 10.1021/nl100161zGoogle Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Knsbg%253D&md5=5c0d70d8f62ffdc2fbebce5b5e4dcb74Light Trapping in Silicon Nanowire Solar CellsGarnett, Erik; Yang, PeidongNano Letters (2010), 10 (3), 1082-1087CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Thin-film structures can decrease the cost of solar power by using inexpensive substrates and a lower quantity and quality of semiconductor material. However, the resulting short optical path length and minority carrier diffusion length necessitates either a high absorption coeff. or good light trapping. Semiconducting nanowire arrays were shown to have low reflective losses compared to planar semiconductors, but their light-trapping properties were not measured. Using optical transmission and photocurrent measurements on thin Si films, ordered arrays of Si nanowires increase the path length of incident solar radiation by up to a factor of 73. This light-trapping path length enhancement factor is above the randomized scattering (Lambertian) limit (2n2 ∼ 25 without a back reflector) and is better than other light-trapping methods. By changing the Si film thickness and nanowire length, there is a competition between improved absorption and increased surface recombination. For nanowire arrays fabricated from 8 μm thick Si films, the enhanced absorption can dominate over surface recombination, even without any surface passivation. These nanowire devices had efficiencies >5%, with short-circuit photocurrents higher than planar control samples.
- 23Martins, E. R.; Li, J.; Liu, Y.; Depauw, V.; Chen, Z.; Zhou, J.; Krauss, T. F. Deterministic Quasi-Random Nanostructures for Photon Control. Nat. Commun. 2013, 4, 2665, DOI: 10.1038/ncomms3665Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c%252FpsVKhuw%253D%253D&md5=26b5c42b94cb424a54893f4043dd83bcDeterministic quasi-random nanostructures for photon controlMartins Emiliano R; Li Juntao; Liu YiKun; Depauw Valerie; Chen Zhanxu; Zhou Jianying; Krauss Thomas FNature communications (2013), 4 (), 2665 ISSN:.Controlling the flux of photons is crucial in many areas of science and technology. Artificial materials with nano-scale modulation of the refractive index, such as photonic crystals, are able to exercise such control and have opened exciting new possibilities for light manipulation. An interesting alternative to such periodic structures is the class of materials known as quasi-crystals, which offer unique advantages such as richer Fourier spectra. Here we introduce a novel approach for designing such richer Fourier spectra, by using a periodic structure that allows us to control its Fourier components almost at will. Our approach is based on binary gratings, which makes the structures easy to replicate and to tailor towards specific applications. As an example, we show how these structures can be employed to achieve highly efficient broad-band light trapping in thin films that approach the theoretical (Lambertian) limit, a problem of crucial importance for photovoltaics.
- 24van Lare, M.-C.; Polman, A. Optimized Scattering Power Spectral Density of Photovoltaic Light-Trapping Patterns. ACS Photonics 2015, 2, 822– 831, DOI: 10.1021/ph500449vGoogle Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVaku7zI&md5=0c32c59344d35ec37cc8a795df38c6ddOptimized Scattering Power Spectral Density of Photovoltaic Light-Trapping Patternsvan Lare, M.-Claire; Polman, AlbertACS Photonics (2015), 2 (7), 822-831CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)The authors present a generic approach for the optimization of light-trapping patterns for thin-film solar cells. The optimization is based on tailoring the spatial frequencies in the light-trapping pattern to the waveguide modes supported by the thin-film solar cell stack. The authors calc. the dispersion relations for waveguide modes in thin-film Si solar cells and use them to define the required spatial frequency band for light trapping. The authors use a Monte Carlo algorithm to optimize the scattering power spectral d. (PSD) of a random array of Mie scatterers on top of a-Si:H cells. The optimized particle array has a PSD that is larger in the desired spatial frequency range than the PSD of a random array and contains contributions at more spatial frequencies than the PSD of a periodic array. Three-dimensional finite-difference time-domain simulations on thin-film solar cells with different light-trapping patterns show that the optimized particle array results in more efficient light trapping than a random array of Mie scatterers. The authors use the same approach to design a random texture and compare this to the Asahi-U-type texture. The optimized texture outperforms the Asahi-U pattern and an optimized periodic pattern. The light-trapping patterns presented avoid the ohmic absorption losses found in metallic (plasmonic) patterns. They can be tailored to specific spatial frequency ranges, do not contain materials that are incompatible with high-temp. processes, nor require patterning of the active layer. Therefore, they are applicable to nearly all types of thin-film solar cells.
- 25Gaucher, A.; Cattoni, A.; Dupuis, C.; Chen, W.; Cariou, R.; Foldyna, M.; Lalouat, L.; Drouard, E.; Seassal, C.; Roca I Cabarrocas, P.; Collin, S. Ultrathin Epitaxial Silicon Solar Cells with Inverted Nanopyramid Arrays for Efficient Light Trapping. Nano Lett. 2016, 16, 5358– 5364, DOI: 10.1021/acs.nanolett.6b01240Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlehsr7N&md5=9c8981d0c50fe3c73aa249c452ed67abUltrathin Epitaxial Silicon Solar Cells with Inverted Nanopyramid Arrays for Efficient Light TrappingGaucher, Alexandre; Cattoni, Andrea; Dupuis, Christophe; Chen, Wanghua; Cariou, Romain; Foldyna, Martin; Lalouat, Loic; Drouard, Emmanuel; Seassal, Christian; Roca i Cabarrocas, Pere; Collin, StephaneNano Letters (2016), 16 (9), 5358-5364CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Ultrathin c-Si solar cells have the potential to drastically reduce costs by saving raw material while maintaining good efficiencies thanks to the excellent quality of monocryst. silicon. However, efficient light trapping strategies must be implemented to achieve high short-circuit currents. We report on the fabrication of both planar and patterned ultrathin c-Si solar cells on glass using low temp. (T < 275 °C), low-cost, and scalable techniques. Epitaxial c-Si layers are grown by PECVD at 160 °C and transferred on a glass substrate by anodic bonding and mech. cleavage. A silver back mirror is combined with a front texturation based on an inverted nanopyramid array fabricated by nanoimprint lithog. and wet etching. We demonstrate a short-circuit c.d. of 25.3 mA/cm2 for an equiv. thickness of only 2.75 μm. External quantum efficiency (EQE) measurements are in very good agreement with FDTD simulations. We infer an optical path enhancement of 10 in the long wavelength range. A simple propagation model reveals that the low photon escape probability of 25% is the key factor in the light trapping mechanism. The main limitations of our current technol. and the potential efficiencies achievable with contact optimization are discussed.
- 26Fountaine, K. T.; Cheng, W.-H.; Bukowsky, C. R.; Atwater, H. A. Near-Unity Unselective Absorption in Sparse InP Nanowire Arrays. ACS Photonics 2016, 3, 1826– 1832, DOI: 10.1021/acsphotonics.6b00341Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFGrsrfK&md5=62c2353bc2a7a291c3607f9cc39c312bNear-Unity Unselective Absorption in Sparse InP Nanowire ArraysFountaine, Katherine T.; Cheng, Wen-Hui; Bukowsky, Colton R.; Atwater, Harry A.ACS Photonics (2016), 3 (10), 1826-1832CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)We exptl. demonstrate near-unity, unselective absorption, broadband, angle-insensitive, and polarization-independent absorption, in sparse InP nanowire arrays, embedded in flexible polymer sheets via geometric control of waveguide modes in two wire motifs: (i) arrays of tapered wires and (ii) arrays of nanowires with varying radii. Sparse arrays of these structures exhibit enhanced absorption due to strong coupling into the first order azimuthal waveguide modes of individual nanowires; wire radius thus controls the spectral region of the absorption enhancement. Whereas arrays of cylindrical wires with uniform radius exhibit narrowband absorption, arrays of tapered wires and arrays with multiple wire radii expand this spectral region and achieve broadband absorption enhancement. Herein, we present an economic, top-down lithog./etch fabrication method that enables fabrication of multiple InP nanowire arrays from a single InP wafer with deliberate control of nanowire radius and taper. Using this method, we create sparse tapered and multiradii InP nanowire arrays and demonstrate optical absorption that is broadband (450-900 nm), angle-insensitive, and near-unity (>90%) in roughly 100 nm planar equivalence of InP. These highly absorbing sparse nanowire arrays represent a promising approach to flexible, high efficiency optoelectronic devices, such as photodetectors, solar cells, and photoelectrochem. devices.
- 27Marko, G.; Prajapati, A.; Shalev, G. Subwavelength Nonimaging Light Concentrators for the Harvesting of the Solar Radiation. Nano Energy 2019, 61, 275– 283, DOI: 10.1016/j.nanoen.2019.04.082Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXos12ht7g%253D&md5=9d0adfb318a5ecc78fccf7f23968dcebSubwavelength nonimaging light concentrators for the harvesting of the solar radiationMarko, Gilad; Prajapati, Ashish; Shalev, GilNano Energy (2019), 61 (), 275-283CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Light trapping and the broadband absorption of the solar radiation is of interest to various solar energy harvesting applications. In the current work, we report a new paradigm for light trapping, that is light trapping based on arrays of subwavelength nonimaging light concentrators (NLCs). We numerically show that silicon NLC arrays provide >75% broadband absorption enhancement of the solar radiation compared with that of optimized nanopillar arrays. The paper focuses on free-floating arrays of subwavelength compd. parabolic concentrators (henceforth CPC arrays) as a case study. The calcns. reveal that CPC arrays function as anti-transmission layers as only few photons transverse the CPC arrays which is in contrast to nanopillar arrays that function as anti-reflection layers. We show that the absorption enhancement in CPC arrays is due to efficient occupation of Mie modes which is motivated by the unique CPC geometry, and we demonstrate light trapping at the Yablonovitch limit. Finally, we examine the performance of a photovoltaic cell based on CPC arrays with respect to base doping levels and surface recombination. We show that the short-circuit c.d. of the CPC-based cell is >75% higher than the short-circuit c.d. of a photovoltaic cell based on optimized nanopillar arrays. We believe that light trapping based on NLC arrays paves the way to various applications such as ultra-thin photovoltaic cells.
- 28Prajapati, A.; Llobet, J.; Antunes, M.; Martins, S.; Fonseca, H.; Calaza, C.; Gaspar, J.; Shalev, G. An Efficient and Deterministic Photon Management Using Deep Subwavelength Features. Nano Energy 2020, 70, 104521, DOI: 10.1016/j.nanoen.2020.104521Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisVSqtbo%253D&md5=64f44e7a5fc9862f3499df09da94efacAn efficient and deterministic photon management using deep subwavelength featuresPrajapati, Ashish; Llobet, Jordi; Antunes, Mariana; Martins, Sofia; Fonseca, Helder; Calaza, Carlos; Gaspar, Joao; Shalev, GilNano Energy (2020), 70 (), 104521CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Light trapping and the broadband absorption of the solar radiation are significant to a plethora of absorption-based photonic devices. Specifically, efficient broadband absorption was recently demonstrated with arrays of subwavelength structures. The current study examines both numerically and exptl. light trapping driven by deep sidewall subwavelength structures (DSSS) in silicon nanopillar (NP) arrays (DSSS arrays). Particularly, the focus is on DSSS geometries that are an inherent outcome of the top-down dry etch approach used in arrays of high aspect ratio NPs due to the periodical operationality of the Bosch dry etch method. ∼10% enhancement in the broadband absorption of DSSS arrays compared with NP arrays is demonstrated numerically, as well as the generation of near-IR absorptivity peaks of ∼25% for DSSS arrays. Importantly, it is shown that the introduction of DSSS systematically blue-shifts the absorptivity peaks of the NP arrays and in this manner a deterministic light trapping is possible. Finally, decrements of ∼40% in direct reflectivity and ∼7% in diffused reflectivity in DSSS arrays realized on silicon wafers is demonstrated exptl.
- 29Yu, Z.; Raman, A.; Fan, S. Fundamental Limit of Light Trapping in Grating Structures. Opt. Express 2010, 18, A366– A380, DOI: 10.1364/oe.18.00a366Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Skt7%252FL&md5=9a1bfbf29b02fbc51be2f0c104aa450fFundamental limit of light trapping in grating structuresYu, Zongfu; Raman, Aaswath; Fan, ShanhuiOptics Express (2010), 18 (S3), A366-A380CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n2, but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile's symmetry on the absorption enhancement limit. Numerical simulations are applied to support the theory. Our findings provide general guidance for the design of grating structures for light-trapping solar cells.
- 30Sturmberg, B. C. P.; Dossou, K. B.; Botten, L. C.; Asatryan, A. A.; Poulton, C. G.; de Sterke, C. M.; McPhedran, R. C. Modal Analysis of Enhanced Absorption in Silicon Nanowire Arrays. Opt. Express 2011, 19, A1067, DOI: 10.1364/OE.19.0A1067Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXht1Omsr7K&md5=4aa51b229eddb87b21e9c55b70147affModal analysis of enhanced absorption in silicon nanowire arraysSturmberg, Bjorn C. P.; Dossou, Kokou B.; Botten, Lindsay C.; Asatryan, Ara A.; Poulton, Christopher G.; Martijn de Sterke, C.; McPhedran, Ross C.Optics Express (2011), 19 (S5), A1067-A1081CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)We analyze the absorption of solar radiation by silicon nanowire arrays, which are being considered for photovoltaic applications. These structures have been shown to have enhanced absorption compared with thin films, however the mechanism responsible for this is not understood. Using a new, semi-analytic model, we show that the enhanced absorption can be attributed to a few modes of the array, which couple well to incident light, overlap well with the nanowires, and exhibit strong Fabry-Perot resonances. For some wavelengths the absorption is further enhanced by slow light effects. We study the evolution of these modes with wavelength to explain the various features of the absorption spectra, focusing first on a dil. array at normal incidence, before generalizing to a dense array and off-normal angles of incidence. The understanding developed will allow for optimization of simple SiNW arrays, as well as the development of more advanced designs.
- 31Chauhan, A.; Prajapati, A.; Calaza, C.; Fonseca, H.; Sousa, P. C.; Llobet, J.; Shalev, G. Near-Field Optical Excitations in Silicon Subwavelength Light Funnel Arrays for Broadband Absorption of the Solar Radiation. Sol. RRL 2021, 5, 2100721, DOI: 10.1002/solr.202100721Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXit1ygur3M&md5=847825689a8677636a2ff713929e9e0eNear-Field Optical Excitations in Silicon Subwavelength Light Funnel Arrays for Broadband Absorption of the Solar RadiationChauhan, Ankit; Prajapati, Ashish; Calaza, Carlos; Fonseca, Helder; Sousa, Patricia C.; Llobet, Jordi; Shalev, GilSolar RRL (2021), 5 (12), 2100721CODEN: SRORAW; ISSN:2367-198X. (Wiley-VCH Verlag GmbH & Co. KGaA)Broadband absorption is pivotal for the realization of green energy based on solar energy. Decoration of photovoltaic cells with arrays of subwavelength formations provides an efficient means for broadband absorption in thin films. Surface arrays of silicon light funnels (LFs) have been suggested as a promising platform to produce broadband absorption that is considerably superior to other subwavelength arrays such as the well-known nanopillar (NP) arrays. The current study explores the underlying mechanism of broadband absorption in LF arrays. To this end, the optical near-field of LF and NP arrays is exptl. probed using a near-field scanning optical microscopy. It is shown that in LF arrays the near-field increases as the array period decreases in contrast with NP arrays in which the near-field decreases with decreasing array period. Also, the exptl. near-field of the arrays follows the numerically calcd. absorption cross section of the array-nested NPs/LFs. Therefore, the origin to the broadband absorption in compact LF arrays is due to field overlap of adjacent LFs which increases the absorption cross section of the individual LFs composing the array. This absorption cross-sectional enhancement coupled with a higher filling ratio in compact arrays produces broadband absorption that is significantly greater than that of NP arrays.
- 32Chauhan, A.; Prajapati, A.; Llobet, J.; Fonseca, H.; Sousa, P. C.; Calaza, C.; Shalev, G. Incorporation of Nano-Features into Surface Photoactive Arrays for Broadband Absorption of the Solar Radiation. Sol. Energy Mater. Sol. Cells 2022, 245, 111864, DOI: 10.2139/ssrn.4089581Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xhslemsr7M&md5=49f1711278ce8fcae04de742796ac738Incorporation of nano-features into surface photoactive arrays for broadband absorption of the solar radiationChauhan, Ankit; Prajapati, Ashish; Llobet, Jordi; Fonseca, Helder; Sousa, Patricia C.; Calaza, Carlos; Shalev, GilSolar Energy Materials & Solar Cells (2022), 245 (), 111864CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)Surface arrays of photoactive materials with subwavelength dimensions are important for energy harvesting applications due to their capacity for broadband and omnidirectional absorption of the solar radiation. It was recently proposed and demonstrated that the absorption performance of such arrays can be further amplified with the introduction of addnl. nano-features. In the current work we consider the incorporation of nano-features into nanopillar (NP) arrays. The considered nano-features are: quasi-nanolenses, sidewall nano-decorations, and decreasing the NP bottom diam. to transform it into a light funnel (LF). The underlying various light trapping mechanisms are examd. using near-field microscopy. Near-field microscopy is used to obtained both high-resoln. far-field imaging, as well as mapping of the near-field photon distributions of the arrays. Firstly, it is shown that the main contribution to far-field reflected photons is from the ambient surrounding the silicon structures. Secondly, the incorporation of the various nano-features induces a decrease in the reflected far-field photons which originate from this ambient region. Also, it is shown how the incorporation of quasi-nanolenses concludes a decrease in far-field photons reflected in the oblique directions with high polar angles, whereas the incorporation of sidewall nano-decorations leads to a decrease in far-field photons reflected in directions of small polar angles. Also, the incorporation of both qNL and sidewall nano-decorations is examd., and light trapping with the LF geometry is discussed and demonstrated. Finally, understanding the underlying light trapping mechanisms will support the deterministic design of subwavelength arrays incorporated with nano-features for efficient harvesting of the solar radiation.
- 33Oh, J.; Yuan, H.-C.; Branz, H. M. An 18.2%-Efficient Black-Silicon Solar Cell Achieved through Control of Carrier Recombination in Nanostructures. Nat. Nanotechnol. 2012, 7, 743– 748, DOI: 10.1038/nnano.2012.166Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVaqur7N&md5=dee4dd39adb901a862bd817a1aa6e539An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructuresOh, Jihun; Yuan, Hao-Chih; Branz, Howard M.Nature Nanotechnology (2012), 7 (11), 743-748CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Silicon nanowire and nanopore arrays promise to reduce manufg. costs and increase the power conversion efficiency of photovoltaic devices. So far, however, photovoltaic cells based on nanostructured silicon exhibit lower power conversion efficiencies than conventional cells due to the enhanced photocarrier recombination assocd. with the nanostructures. Here, surface recombination and Auger recombination in wafer-based nanostructured silicon solar cells are identified and sep. measured. By identifying the regimes of junction doping concn. in which each mechanism dominates, it is possible to design and fabricate an independently confirm 18.2%-efficient nanostructured black-silicon' cell that does not need the antireflection coating layer(s) normally required to reach a comparable performance level. The results suggest design rules for efficient high-surface-area solar cells with nano- and microstructured semiconductor absorbers.
- 34Leutz, R.; Suzuki, A. Nonimaging Fresnel Lenses; Springer Berlin, Heidelberg: Berlin Heidelberg, 2001.Google ScholarThere is no corresponding record for this reference.
- 35Miller, D. C.; Kurtz, S. R. Durability of Fresnel lenses: A review specific to the concentrating photovoltaic application. Sol. Energy Mater. Sol. Cells 2011, 95, 2037– 2068, DOI: 10.1016/j.solmat.2011.01.031Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntlWrsL8%253D&md5=4bc1ac7e5af64a6c814123469897eaa5Durability of Fresnel lenses: A review specific to the concentrating photovoltaic applicationMiller, David C.; Kurtz, Sarah R.Solar Energy Materials & Solar Cells (2011), 95 (8), 2037-2068CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)A review. The durability of Fresnel lenses used in the concg. photovoltaic (CPV) application is reviewed from the literature. The examn. here primarily concerns monolithic lenses constructed of poly(Me methacrylate) (PMMA), with supplemental examn. of silicone-on-glass (SOG) composite lenses. For PMMA, the review includes the topics of: optical durability (loss of transmittance with age); discoloration (the wavelength-specific loss of transmittance); microcrazing and hazing; fracture and mech. fatigue; phys. aging, creep, shape change, buckling, and warping; and solid erosion. Soiling, or the accumulation of particulate matter, is examd. in the following contexts: its magnitude of redn. in transmittance; variation with time, module tilt, and wavelength; the processes of adhesion and accumulation; particle size, distribution, compn., and morphol.; and its prevention. Photodegrdn. and thermal decompn., mechanisms enabling aging, are examd. relative to the CPV-specific environment. VAspects specific to SOG lenses include: solarization of the glass superstrate; corrosion of glass; delamination of the silicone/glass interface; change in focus due to thermal misfit between the laminate layers; and the chem. stability of poly(dimethylsiloxane) (PDMS). Recommendations for future research are provided, based on the most important and the least explored topics.
- 36Xie, W. T.; Dai, Y.; Wang, R. Z.; Sumathy, K. Concentrated Solar Energy Applications Using Fresnel Lenses : A Review. Renewable Sustainable Energy Rev. 2011, 15, 2588– 2606, DOI: 10.1016/j.rser.2011.03.031Google ScholarThere is no corresponding record for this reference.
- 37Sze, S. M. Physics of Semiconductor Devices, 2nd ed.; Wiley: New York, 1981.Google ScholarThere is no corresponding record for this reference.
- 38Lochmann, W.; Haug, A. Phonon-assisted Auger recombination in Si with direct calculation of the overlap integrals. Solid State Commun. 1980, 35, 553– 556, DOI: 10.1016/0038-1098(80)90896-0Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXlvFKgtLg%253D&md5=6e8fade9aeae8fa1fc5dd5e2096d8e44Phonon-assisted Auger recombination in silicon with direct calculation of the overlap integralsLochmann, W.; Haug, A.Solid State Communications (1980), 35 (7), 553-6CODEN: SSCOA4; ISSN:0038-1098.The overlap integrals are calcd for Si by means of the full zone double group k.p-method whereas they are usually roughly estd. The results confirm that phonon-assisted Auger recombination is the predominating radiationless recombination mechanism in indirect band gap semiconductors. This holds not only for highly doped materials but also for electron-hole drops.
- 39Green, M. A.; Keevers, M. J. Optical Properties of Intrinsic Silicon at 300 K. Prog. Photovoltaics Res. Appl. 1995, 3, 189– 192, DOI: 10.1002/pip.4670030303Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXnvVakuro%253D&md5=2e3aabe5a0d717ba06aaec6c811e2d19Optical properties of intrinsic silicon at 300 KGreen, Martin A.; Keevers, Mark J.Progress in Photovoltaics (1995), 3 (3), 189-92CODEN: PPHOED; ISSN:1062-7995. (Wiley)An updated tabulation is presented of the optical properties of intrinsic silicon relevant to solar cell calcns. The absorption coeff., refractive index, and extinction coeff. at 300 K are tabulated over the 0.25-1.45 μm wavelength range at 0.01 μm intervals.
- 40Hoex, B.; Heil, S. B. S.; Langereis, E.; van de Sanden, M. C. M.; Kessels, W. M. M. Ultralow Surface Recombination of C-Si Substrates Passivated by Plasma-Assisted Atomic Layer Deposited Al2O3. Appl. Phys. Lett. 2006, 89, 042112, DOI: 10.1063/1.2240736Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XotFSmtb4%253D&md5=4935f3e06ded9894a3e74433076321d6Ultralow surface recombination of c-Si substrates passivated by plasma-assisted atomic layer deposited Al2O3Hoex, B.; Heil, S. B. S.; Langereis, E.; van de Sanden, M. C. M.; Kessels, W. M. M.Applied Physics Letters (2006), 89 (4), 042112/1-042112/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Excellent surface passivation of c-Si has been achieved by Al2O3 films prepd. by plasma-assisted at. layer deposition, yielding effective surface recombination velocities of 2 and 13 cm/s on low resistivity n- and p-type c-Si, resp. These results obtained for ∼30 nm thick Al2O3 films are comparable to state-of-the-art results when employing thermal oxide as used in record-efficiency c-Si solar cells. A 7 nm thin Al2O3 film still yields an effective surface recombination velocity of 5 cm/s on n-type silicon.
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Abstract
Figure 1
Figure 1. (a) Illustrations of the various considered Fresnel complexes with the relevant geometrical parameters. (b) θ-dependency of the broadband absorption of the full complexes, the arrays, and the substrates for the various considered geometries. (c) θ-dependency of the broadband reflection and the broadband transmission for the concave complex, the convex complex, NP complex, and θ = 0° complex. (d) AOI-dependency of the θ = −35° and the θ = 15° arrays (both with tcircle = 30 nm). Note: the NP complex is also shown for reference.
Figure 2
Figure 2. (a) θ-dependency of the lateral and vertical irradiance for the full complexes, for the arrays, and for the substrates. The NP array is also shown for reference. The arrow next to E reflects the direction of the impinging irradiance electric field. (b) θ-dependency of the broadband absorption depth profiles for convex and concave arrays, both with tcircle = 30 nm. The NP array is also shown for reference. The x-axis zero value marks the top of the substrate. (c) Cross-sections showing the normalized APD under broadband illumination for θ = 0, 15, 35, and 55°.
Figure 3
Figure 3. (a) Illustrations showing the considered PV cells. (b) I–V curves under broadband illumination for selected θ values and an absorber doping concentration of 1017 cm–3. (c) Dependency of Jsc, Voc, and nPCE on absorber doping level for the selected θ values. (d) SRV-dependency of Jsc, Voc, and nPCE for the selected θ values.
References
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- 3Yan, T.; Li, Z.; Cao, F.; Chen, J.; Wu, L.; Fang, X. An All-Organic Self-Powered Photodetector with Ultraflexible Dual-Polarity Output for Biosignal Detection. Adv. Mater. 2022, 34, 2201303, DOI: 10.1002/adma.2022013033https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xhs12gtLbO&md5=0b9080c626c77c7c4cde2e7f5f770a6cAn All-Organic Self-Powered Photodetector with Ultraflexible Dual-Polarity Output for Biosignal DetectionYan, Tingting; Li, Ziqing; Cao, Fa; Chen, Jiaxin; Wu, Limin; Fang, XiaoshengAdvanced Materials (Weinheim, Germany) (2022), 34 (30), 2201303CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Endowing photodetectors with mech. flexibility and actual functionality are current research issues in developing optoelectronic devices. However, rigid metal-based or metal-oxide-based electrodes remain a block to the realization of ultraflexible electronics. Thus, an ultraflexible all-org. photodetector (all-OPD) is designed by innovatively introducing sym. org. electrodes PH1000/PH1000 to substitute the widely applied indium-doped tin oxide (ITO)/Ag electrodes. Specifically, this all-OPD exhibits a high self-powered responsivity (R) of over 100 mA W-1 among 500-600 nm and the photocurrent remains about 80% of the original performance after being bent 20 000 circles, and can output steady biosignals for photo-plethysmog. (PPG) application. More importantly, this all-OPD outputs dual-polarity photocurrent as it is flipped or folded. Benefitting from the ordered phase distribution and designed Schottky barrier heights, the photogenerated holes will be transferred and collected by nearer electrode, while electrons will be trapped in the thick bulk heterojunction (BHJ) as a result of the long channel. This work offers a new avenue toward developing a multifunctional and ultraflexible all-OPD with a straightforward all-soln. method, and it is expected to be more compatible in complex application scenarios.
- 4Yablonovitch, E. Statistical Ray Optics. J. Opt. Soc. Am. 1982, 72, 899, DOI: 10.1364/JOSA.72.000899There is no corresponding record for this reference.
- 5Yu, Z.; Raman, A.; Fan, S. Fundamental Limit of Light Trapping in Grating Structures. Opt. Express 2010, 18, A366– A380, DOI: 10.1364/OE.18.00A3665https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Skt7%252FL&md5=9a1bfbf29b02fbc51be2f0c104aa450fFundamental limit of light trapping in grating structuresYu, Zongfu; Raman, Aaswath; Fan, ShanhuiOptics Express (2010), 18 (S3), A366-A380CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n2, but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile's symmetry on the absorption enhancement limit. Numerical simulations are applied to support the theory. Our findings provide general guidance for the design of grating structures for light-trapping solar cells.
- 6Yu, Z.; Raman, A.; Fan, S. Fundamental Limit of Nanophotonic Light Trapping in Solar Cells. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 17491– 17496, DOI: 10.1073/pnas.10082961076https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlartbzM&md5=8a4a452e53ec41702c28a630d601efcaFundamental limit of nanophotonic light trapping in solar cellsYu, Zongfu; Raman, Aaswath; Fan, ShanhuiProceedings of the National Academy of Sciences of the United States of America (2010), 107 (41), 17491-17496, S17491/1-S17491/4CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Establishing the fundamental limit of nanophotonic light-trapping schemes is of paramount importance and is becoming increasingly urgent for current solar cell research. The std. theory of light trapping demonstrated that absorption enhancement in a medium cannot exceed a factor of 4n2/sin2θ, where n is the refractive index of the active layer, and θ is the angle of the emission cone in the medium surrounding the cell. This theory, however, is not applicable in the nanophotonic regime. Here we develop a statistical temporal coupled-mode theory of light trapping based on a rigorous electromagnetic approach. Our theory reveals that the conventional limit can be substantially surpassed when optical modes exhibit deep-subwavelength-scale field confinement, opening new avenues for highly efficient next-generation solar cells.
- 7Callahan, D. M.; Munday, J. N.; Atwater, H. a. Solar Cell Light Trapping beyond the Ray Optic Limit. Nano Lett. 2012, 12, 214– 218, DOI: 10.1021/nl203351k7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhs1Slsr%252FK&md5=01b05dea21d6bd5cb5a863896a480d98Solar Cell Light Trapping beyond the Ray Optic LimitCallahan, Dennis M.; Munday, Jeremy N.; Atwater, Harry A.Nano Letters (2012), 12 (1), 214-218CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Yablonovitch proposed a thermodn. limit on light trapping within homogeneous semiconductor slabs, which implied a min. thickness needed to fully absorb the solar spectrum. However, this limit is valid for geometrical optics but not for a new generation of sub-wavelength solar absorbers such as ultrathin or inhomogeneously structured cells, wire-based cells, photonic crystal-based cells and plasmonic cells. The key to exceeding the conventional ray optic or so-called ergodic light trapping limit is in designing an elevated local d. of optical states (LDOS) for the absorber. Also, for any semiconductor it is always possible to exceed the ray optic light trapping limit and use these principles to design a no. of new solar absorbers with the key feature of having an elevated LDOS within the absorbing region of the device, opening new avenues for solar cell design and cost redn.
- 8Sturmberg, B. C. P.; Dossou, K. B.; Botten, L. C.; Asatryan, A. A.; Poulton, C. G.; McPhedran, R. C.; de Sterke, C. M. Absorption Enhancing Proximity Effects in Aperiodic Nanowire Arrays. Opt. Express 2013, 21, A964– A969, DOI: 10.1364/OE.21.00A964There is no corresponding record for this reference.
- 9Hu, L.; Chen, G. Analysis of Optical Absorption in Silicon Nanowire Arrays for Photovoltaic Applications. Nano Lett. 2007, 7, 3249– 3252, DOI: 10.1021/nl071018b9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFehu7fK&md5=afffda995213a968fb853a85827f4a54Analysis of Optical Absorption in Silicon Nanowire Arrays for Photovoltaic ApplicationsHu, Lu; Chen, GangNano Letters (2007), 7 (11), 3249-3252CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)An anal. of the optical absorption in Si nanowire arrays for application in solar cells is presented. The effects of wire diam., length, and filling ratio on the absorptance of nanowire arrays were simulated. Nanowire arrays with moderate filling ratios have a lower reflectance than thin films. At high frequencies nanowire arrays have higher absorptance than thin films. At low frequencies nanowire arrays absorb less but can be designed to approach that of the film by changing the filling ratio.
- 10Spinelli, P.; Verschuuren, M. A.; Polman, A. Broadband Omnidirectional Antireflection Coating Based on Subwavelength Surface Mie Resonators. Nat. Commun. 2012, 3, 692, DOI: 10.1038/ncomms169110https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC383lt12guw%253D%253D&md5=c9aa8663017049f503952f5a43f789bcBroadband omnidirectional antireflection coating based on subwavelength surface Mie resonatorsSpinelli P; Verschuuren M A; Polman ANature communications (2012), 3 (), 692 ISSN:.Reflection is a natural phenomenon that occurs when light passes the interface between materials with different refractive index. In many applications, such as solar cells or photodetectors, reflection is an unwanted loss process. Many ways to reduce reflection from a substrate have been investigated so far, including dielectric interference coatings, surface texturing, adiabatic index matching and scattering from plasmonic nanoparticles. Here we present an entirely new concept that suppresses the reflection of light from a silicon surface over a broad spectral range. A two-dimensional periodic array of subwavelength silicon nanocylinders designed to possess strongly substrate-coupled Mie resonances yields almost zero total reflectance over the entire spectral range from the ultraviolet to the near-infrared. This new antireflection concept relies on the strong forward scattering that occurs when a scattering structure is placed in close proximity to a high-index substrate with a high optical density of states.
- 11Kim, S. K.; Zhang, X.; Hill, D. J.; Song, K. D.; Park, J. S.; Park, H. G.; Cahoon, J. F. Doubling Absorption in Nanowire Solar Cells with Dielectric Shell Optical Antennas. Nano Lett. 2015, 15, 753– 758, DOI: 10.1021/nl504462e11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitFOku77M&md5=d09228b384cdba69fe2cd1f004f932b9Doubling Absorption in Nanowire Solar Cells with Dielectric Shell Optical AntennasKim, Sun-Kyung; Zhang, Xing; Hill, David J.; Song, Kyung-Deok; Park, Jin-Sung; Park, Hong-Gyu; Cahoon, James F.Nano Letters (2015), 15 (1), 753-758CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Semiconductor nanowires (NWs) often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indexes of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small vols. of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely det. the economic viability of NW-based solar cells. Here, the authors demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielec. shells. Scattering and absorption measurements on Si NWs coated with shells of SiNx or SiOx exhibit a broadband enhancement of light absorption by ∼50-200% and light scattering by ∼200-1000%. The increased light-matter interaction leads to a ∼ 80% increase in short-circuit c.d. in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the exptl. results and indicate the dielec.-shell effect to be a general phenomenon for groups IV, II-VI, and III-V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approx. double the efficiency of NW-based solar cells.
- 12Li, Y.; Li, M.; Fu, P.; Li, R.; Song, D.; Shen, C.; Zhao, Y. A Comparison of Light-Harvesting Performance of Silicon Nanocones and Nanowires for Radial-Junction Solar Cells. Sci. Rep. 2015, 5, 11532, DOI: 10.1038/srep1153212https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFyhsbzO&md5=2a61e9cf7d6a2f47914107538f45504dA comparison of light-harvesting performance of silicon nanocones and nanowires for radial-junction solar cellsLi, Yingfeng; Li, Meicheng; Fu, Pengfei; Li, Ruike; Song, Dandan; Shen, Chao; Zhao, YanScientific Reports (2015), 5 (), 11532CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)Silicon nanorod based radial-junction solar cells are competitive alternatives to traditional planar silicon solar cells. In various silicon nanorods, nanocone is always considered to be better than nanowire in light-absorption. Nevertheless, we find that this notion isn't absolutely correct. Silicon nanocone is indeed significantly superior over nanowire in light-concn. due to its continuous diams., and thus resonant wavelengths excited. However, the concd. light can't be effectively absorbed and converted to photogenerated carriers, since its propagation path in silicon nanocone is shorter than that in nanowire. The results provide crit. clues for the design of silicon nanorod based radial-junction solar cells.
- 13Wong, A. B.; Brittman, S.; Yu, Y.; Dasgupta, N. P.; Yang, P. Core-Shell CdS-Cu2S Nanorod Array Solar Cells. Nano Lett. 2015, 15, 4096– 4101, DOI: 10.1021/acs.nanolett.5b0120313https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXoslylsb0%253D&md5=2164fc119f727db3258135f71eb7c905Core-Shell CdS-Cu2S Nanorod Array Solar CellsWong, Andrew Barnabas; Brittman, Sarah; Yu, Yi; Dasgupta, Neil P.; Yang, PeidongNano Letters (2015), 15 (6), 4096-4101CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)As an earth-abundant p-type semiconductor, copper sulfide (Cu2S) is an attractive material for application in photovoltaic devices. However, it suffers from a minority carrier diffusion length that is less than the length required for complete light absorption. Core-shell nanowires and nanorods have the potential to alleviate this difficulty because they decouple the length scales of light absorption and charge collection. To achieve this geometry using Cu2S, cation exchange was applied to an array of CdS nanorods to produce well-defined CdS-Cu2S core-shell nanorods. Previous work demonstrated single-nanowire photovoltaic devices from this material system, but the cation exchange chem. was applied to nanorod arrays to produce ensemble-level devices with microscale sizes. The core-shell nanorod array devices show power conversion efficiencies of up to 3.8%. These devices are stable when measured in air after nearly one month of storage in a desiccator. These results are a 1st step in the development of large-area nanostructured Cu2S-based photovoltaics that can be processed from soln.
- 14Nowzari, A.; Heurlin, M.; Jain, V.; Storm, K.; Hosseinnia, A.; Anttu, N.; Borgström, M. T.; Pettersson, H.; Samuelson, L. A Comparative Study of Absorption in Vertically and Laterally Oriented InP Core-Shell Nanowire Photovoltaic Devices. Nano Lett. 2015, 15, 1809– 1814, DOI: 10.1021/nl504559g14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXisF2htbc%253D&md5=fdb9c6af3ce66f3d43973892652978bdA Comparative Study of Absorption in Vertically and Laterally Oriented InP Core-Shell Nanowire Photovoltaic DevicesNowzari, Ali; Heurlin, Magnus; Jain, Vishal; Storm, Kristian; Hosseinnia, Ali; Anttu, Nicklas; Borgstroem, Magnus T.; Pettersson, Haakan; Samuelson, LarsNano Letters (2015), 15 (3), 1809-1814CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The absorption in InP core-shell nanowire p-i-n junctions was compared in lateral and vertical orientation. Arrays of vertical core-shell nanowires with 400 nm pitch and 280 nm diam., as well as corresponding lateral single core-shell nanowires, were configured as photovoltaic devices. The photovoltaic characteristics of the samples, measured under 1 sun illumination, showed a higher absorption in lateral single nanowires compared to that in individual vertical nanowires, arranged in arrays with 400 nm pitch. Electromagnetic modeling of the structures confirmed the exptl. observations and showed that the absorption in a vertical nanowire in an array depends strongly on the array pitch. Depending on the array pitch, absorption in a vertical nanowire can be lower or higher than that in a lateral nanowire with equal absorption predicted at a pitch of 510 nm for the nanowire geometry. The described technol. facilitates quant. comparison of absorption in laterally and vertically oriented core-shell nanowire p-i-n junctions and can aid in the design, optimization, and performance evaluation of nanowire-based core-shell photovoltaic devices.
- 15Wallentin, J.; Anttu, N.; Asoli, D.; Huffman, M.; Aberg, I.; Magnusson, M. H.; Siefer, G.; Fuss-Kailuweit, P.; Dimroth, F.; Witzigmann, B.; Xu, H. Q.; Samuelson, L.; Deppert, K.; Borgström, M. T. InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit. Science 2013, 339, 1057– 1060, DOI: 10.1126/science.123096915https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjtVGjs7s%253D&md5=efdf6db71841214bb23468af37ef5558InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics LimitWallentin, Jesper; Anttu, Nicklas; Asoli, Damir; Huffman, Maria; Aaberg, Ingvar; Magnusson, Martin H.; Siefer, Gerald; Fuss-Kailuweit, Peter; Dimroth, Frank; Witzigmann, Bernd; Xu, H. Q.; Samuelson, Lars; Deppert, Knut; Borgstroem, Magnus T.Science (Washington, DC, United States) (2013), 339 (6123), 1057-1060CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Photovoltaics based on nanowire arrays could reduce cost and materials consumption compared with planar devices but have exhibited low efficiency of light absorption and carrier collection. We fabricated a variety of millimeter-sized arrays of p-type/intrinsic/n-type (p-i-n) doped InP nanowires and found that the nanowire diam. and the length of the top n-segment were crit. for cell performance. Efficiencies up to 13.8% (comparable to the record planar InP cell) were achieved by using resonant light trapping in 180-nm-diam. nanowires that only covered 12% of the surface. The share of sunlight converted into photocurrent (71%) was six times the limit in a simple ray optics description. Furthermore, the highest open-circuit voltage of 0.906 V exceeds that of its planar counterpart, despite about 30 times higher surface-to-vol. ratio of the nanowire cell.
- 16Aberg, I.; Vescovi, G.; Asoli, D.; Naseem, U.; Gilboy, J. P.; Sundvall, C.; Dahlgren, A.; Svensson, K. E.; Anttu, N.; Bjork, M. T. A GaAs Nanowire Array Solar Cell with 15.3 % Efficiency at 1 Sun. IEEE J. Photovoltaics 2016, 6, 185– 190, DOI: 10.1109/jphotov.2015.2484967There is no corresponding record for this reference.
- 17Shalev, G.; Schmitt, S.; Brönstrup, G.; Christiansen, S. Maximizing the Ultimate Absorption Efficiency of Vertically-Aligned Semiconductor Nanowire Arrays with Wires of a Low Absorption Cross-Section. Nano Energy 2015, 12, 801– 809, DOI: 10.1016/j.nanoen.2015.01.04817https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXivFWmt7o%253D&md5=1405cfe2b1a285c2995ded0fd96dd819Maximizing the ultimate absorption efficiency of vertically-aligned semiconductor nanowire arrays with wires of a low absorption cross-sectionShalev, Gil; Schmitt, Sebastian W.; Broenstrup, Gerald; Christiansen, SilkeNano Energy (2015), 12 (), 801-809CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Single semiconducting nanowires with sub-wavelength diams. exhibit superior light absorption, and hence triggered a vivid discussion regarding the application of these nanostructures into future generations of high efficiency solar cells. We examine the transition from a single highly absorbing silicon wire into an array composed of such individuals in order to validate the application of these into solar harvesting devices. We use finite-difference time-domain simulations to show that the coupling of the Fabry-Perot oscillations with the waveguide resonances inside the wires has a significant effect on the array absorption. For example, the ultimate absorption efficiency of a square-tiled wire array under normal incidence (array period of 0.5 μm, wire diam. of 0.4 μm and wire height of 2) is 81% higher than a 2 μm thin-film when the Fabry-Perot oscillations are considered and 37% higher when these oscillations are not considered. This coupling screens out the contribution of the waveguide modes to the array absorption and therefore, unlike previously published work, we eliminate the contribution of the Fabry-Perot oscillations. In this manner we demonstrate the absorption enhancement due to waveguide modes, and general correlations between the nanowire geometry and the overall array absorption are presented. First, we show that once an isolated wire with high absorption cross-section is nested inside an array its absorption decreases due to wire proximity effects. Secondly, the array absorption is maximized with relatively wide wires of low absorption cross-sections. We show that a 75 nm wire inside an square-tiled array with 2 μm period has an av. absorption efficiency factor of 6.5 and the av. relative absorption of the array is 0.5%, while the same wire nested inside an array of a 0.25 μm period exhibits 2.3 av. absorption efficiency factor and the array exhibits av. relative absorption of 9.85%. Finally, there is an optimized wire diam. that once exceeded the array absorption converges to that of a continuous film. For example, the max. absorption of 0.5 μm array is obtained with wire diam. of 0.4 μm where a decrease in relative absorption is recorded for arrays with wires exceeding 0.4 μm.
- 18Huang, Y.-F.; Chattopadhyay, S.; Jen, Y.-J.; Peng, C.-Y.; Liu, T.-A.; Hsu, Y.-K.; Pan, C.-L.; Lo, H.-C.; Hsu, C.-H.; Chang, Y.-H.; Lee, C.-S.; Chen, K.-H.; Chen, L.-C. Improved Broadband and Quasi-Omnidirectional Anti-Reflection Properties with Biomimetic Silicon Nanostructures. Nat. Nanotechnol. 2007, 2, 770– 774, DOI: 10.1038/nnano.2007.38918https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtlyktL7F&md5=dcfb0c253b6fad4b8be25fdc19e1ad24Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructuresHuang, Yi-Fan; Chattopadhyay, Surojit; Jen, Yi-Jun; Peng, Cheng-Yu; Liu, Tze-An; Hsu, Yu-Kuei; Pan, Ci-Ling; Lo, Hung-Chun; Hsu, Chih-Hsun; Chang, Yuan-Huei; Lee, Chih-Shan; Chen, Kuei-Hsien; Chen, Li-ChyongNature Nanotechnology (2007), 2 (12), 770-774CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A simple aperiodic array of Si nanotips on a 6-in. wafer with a sub-wavelength structure can suppress the reflection of light at a range of wavelengths from the UV, through the visible part of the spectrum, to the THz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the Si result from changes in the refractive index caused by variations in the height of the Si nanotips, and can be simulated with models that were used to explain the low reflection from moth eyes. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electrooptical devices for the military.
- 19Jeong, S.; McGehee, M. D.; Cui, Y. All-Back-Contact Ultra-Thin Silicon Nanocone Solar Cells with 13.7% Power Conversion Efficiency. Nat. Commun. 2013, 4, 2950, DOI: 10.1038/ncomms395019https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c3ls12mtA%253D%253D&md5=9111dac4d851f142281b9f2a403a100bAll-back-contact ultra-thin silicon nanocone solar cells with 13.7% power conversion efficiencyJeong Sangmoo; McGehee Michael D; Cui YiNature communications (2013), 4 (), 2950 ISSN:.Thinner Si solar cells with higher efficiency can make a Si photovoltaic system a cost-effective energy solution, and nanostructuring has been suggested as a promising method to make thin Si an effective absorber. However, thin Si solar cells with nanostructures are not efficient because of severe Auger recombination and increased surface area, normally yielding <50% EQE with short-wavelength light. Here we demonstrate >80% EQEs at wavelengths from 400 to 800 nm in a sub-10-μm-thick Si solar cell, resulting in 13.7% power conversion efficiency. This significant improvement was achieved with an all-back-contact design preventing Auger recombination and with a nanocone structure having less surface area than any other nanostructures for solar cells. The device design principles presented here balance the photonic and electronic effects together and are an important step to realizing highly efficient, thin Si and other types of thin solar cells.
- 20Savin, H.; Repo, P.; von Gastrow, G.; Ortega, P.; Calle, E.; Garín, M.; Alcubilla, R. Black Silicon Solar Cells with Interdigitated Back-Contacts Achieve 22.1% Efficiency. Nat. Nanotechnol. 2015, 10, 624– 628, DOI: 10.1038/nnano.2015.8920https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlOhu7rO&md5=a4074ebeb81334033a0dc2f6c6c7b132Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiencySavin, Hele; Repo, Paivikki; von Gastrow, Guillaume; Ortega, Pablo; Calle, Eric; Garin, Moises; Alcubilla, RamonNature Nanotechnology (2015), 10 (7), 624-628CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)The nanostructuring of silicon surfaces-known as black silicon-is a promising approach to eliminate front-surface reflection in photovoltaic devices without the need for a conventional antireflection coating. This might lead to both an increase in efficiency and a redn. in the manufg. costs of solar cells. However, all previous attempts to integrate black silicon into solar cells have resulted in cell efficiencies well below 20% due to the increased charge carrier recombination at the nanostructured surface. Here, we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing excellent chem. and elec. passivation. We demonstrate that efficiencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have real potential for industrial prodn. Furthermore, we show that the use of black silicon can result in a 3% increase in daily energy prodn. when compared with a ref. cell with the same efficiency, due to its better angular acceptance.
- 21Brongersma, M. L.; Cui, Y.; Fan, S. Light Management for Photovoltaics Using High-Index Nanostructures. Nat. Mater. 2014, 13, 451– 460, DOI: 10.1038/nmat392121https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmsFamur0%253D&md5=3879a9839d88793a0e13953f89ff9235Light management for photovoltaics using high-index nanostructuresBrongersma, Mark L.; Cui, Yi; Fan, ShanhuiNature Materials (2014), 13 (5), 451-460CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)A review. High-performance photovoltaic cells use semiconductors to convert sunlight into clean elec. power, and transparent dielecs. or conductive oxides as antireflection coatings. A common feature of these materials is their high refractive index. Whereas high-index materials in a planar form tend to produce a strong, undesired reflection of sunlight, high-index nanostructures afford new ways to manipulate light at a subwavelength scale. For example, nanoscale wires, particles and voids support strong optical resonances that can enhance and effectively control light absorption and scattering processes. As such, they provide ideal building blocks for novel, broadband antireflection coatings, light-trapping layers and super-absorbing films. This Review discusses some of the recent developments in the design and implementation of such photonic elements in thin-film photovoltaic cells.
- 22Garnett, E.; Yang, P. Light Trapping in Silicon Nanowire Solar Cells. Nano Lett. 2010, 10, 1082– 1087, DOI: 10.1021/nl100161z22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Knsbg%253D&md5=5c0d70d8f62ffdc2fbebce5b5e4dcb74Light Trapping in Silicon Nanowire Solar CellsGarnett, Erik; Yang, PeidongNano Letters (2010), 10 (3), 1082-1087CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Thin-film structures can decrease the cost of solar power by using inexpensive substrates and a lower quantity and quality of semiconductor material. However, the resulting short optical path length and minority carrier diffusion length necessitates either a high absorption coeff. or good light trapping. Semiconducting nanowire arrays were shown to have low reflective losses compared to planar semiconductors, but their light-trapping properties were not measured. Using optical transmission and photocurrent measurements on thin Si films, ordered arrays of Si nanowires increase the path length of incident solar radiation by up to a factor of 73. This light-trapping path length enhancement factor is above the randomized scattering (Lambertian) limit (2n2 ∼ 25 without a back reflector) and is better than other light-trapping methods. By changing the Si film thickness and nanowire length, there is a competition between improved absorption and increased surface recombination. For nanowire arrays fabricated from 8 μm thick Si films, the enhanced absorption can dominate over surface recombination, even without any surface passivation. These nanowire devices had efficiencies >5%, with short-circuit photocurrents higher than planar control samples.
- 23Martins, E. R.; Li, J.; Liu, Y.; Depauw, V.; Chen, Z.; Zhou, J.; Krauss, T. F. Deterministic Quasi-Random Nanostructures for Photon Control. Nat. Commun. 2013, 4, 2665, DOI: 10.1038/ncomms366523https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c%252FpsVKhuw%253D%253D&md5=26b5c42b94cb424a54893f4043dd83bcDeterministic quasi-random nanostructures for photon controlMartins Emiliano R; Li Juntao; Liu YiKun; Depauw Valerie; Chen Zhanxu; Zhou Jianying; Krauss Thomas FNature communications (2013), 4 (), 2665 ISSN:.Controlling the flux of photons is crucial in many areas of science and technology. Artificial materials with nano-scale modulation of the refractive index, such as photonic crystals, are able to exercise such control and have opened exciting new possibilities for light manipulation. An interesting alternative to such periodic structures is the class of materials known as quasi-crystals, which offer unique advantages such as richer Fourier spectra. Here we introduce a novel approach for designing such richer Fourier spectra, by using a periodic structure that allows us to control its Fourier components almost at will. Our approach is based on binary gratings, which makes the structures easy to replicate and to tailor towards specific applications. As an example, we show how these structures can be employed to achieve highly efficient broad-band light trapping in thin films that approach the theoretical (Lambertian) limit, a problem of crucial importance for photovoltaics.
- 24van Lare, M.-C.; Polman, A. Optimized Scattering Power Spectral Density of Photovoltaic Light-Trapping Patterns. ACS Photonics 2015, 2, 822– 831, DOI: 10.1021/ph500449v24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVaku7zI&md5=0c32c59344d35ec37cc8a795df38c6ddOptimized Scattering Power Spectral Density of Photovoltaic Light-Trapping Patternsvan Lare, M.-Claire; Polman, AlbertACS Photonics (2015), 2 (7), 822-831CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)The authors present a generic approach for the optimization of light-trapping patterns for thin-film solar cells. The optimization is based on tailoring the spatial frequencies in the light-trapping pattern to the waveguide modes supported by the thin-film solar cell stack. The authors calc. the dispersion relations for waveguide modes in thin-film Si solar cells and use them to define the required spatial frequency band for light trapping. The authors use a Monte Carlo algorithm to optimize the scattering power spectral d. (PSD) of a random array of Mie scatterers on top of a-Si:H cells. The optimized particle array has a PSD that is larger in the desired spatial frequency range than the PSD of a random array and contains contributions at more spatial frequencies than the PSD of a periodic array. Three-dimensional finite-difference time-domain simulations on thin-film solar cells with different light-trapping patterns show that the optimized particle array results in more efficient light trapping than a random array of Mie scatterers. The authors use the same approach to design a random texture and compare this to the Asahi-U-type texture. The optimized texture outperforms the Asahi-U pattern and an optimized periodic pattern. The light-trapping patterns presented avoid the ohmic absorption losses found in metallic (plasmonic) patterns. They can be tailored to specific spatial frequency ranges, do not contain materials that are incompatible with high-temp. processes, nor require patterning of the active layer. Therefore, they are applicable to nearly all types of thin-film solar cells.
- 25Gaucher, A.; Cattoni, A.; Dupuis, C.; Chen, W.; Cariou, R.; Foldyna, M.; Lalouat, L.; Drouard, E.; Seassal, C.; Roca I Cabarrocas, P.; Collin, S. Ultrathin Epitaxial Silicon Solar Cells with Inverted Nanopyramid Arrays for Efficient Light Trapping. Nano Lett. 2016, 16, 5358– 5364, DOI: 10.1021/acs.nanolett.6b0124025https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlehsr7N&md5=9c8981d0c50fe3c73aa249c452ed67abUltrathin Epitaxial Silicon Solar Cells with Inverted Nanopyramid Arrays for Efficient Light TrappingGaucher, Alexandre; Cattoni, Andrea; Dupuis, Christophe; Chen, Wanghua; Cariou, Romain; Foldyna, Martin; Lalouat, Loic; Drouard, Emmanuel; Seassal, Christian; Roca i Cabarrocas, Pere; Collin, StephaneNano Letters (2016), 16 (9), 5358-5364CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Ultrathin c-Si solar cells have the potential to drastically reduce costs by saving raw material while maintaining good efficiencies thanks to the excellent quality of monocryst. silicon. However, efficient light trapping strategies must be implemented to achieve high short-circuit currents. We report on the fabrication of both planar and patterned ultrathin c-Si solar cells on glass using low temp. (T < 275 °C), low-cost, and scalable techniques. Epitaxial c-Si layers are grown by PECVD at 160 °C and transferred on a glass substrate by anodic bonding and mech. cleavage. A silver back mirror is combined with a front texturation based on an inverted nanopyramid array fabricated by nanoimprint lithog. and wet etching. We demonstrate a short-circuit c.d. of 25.3 mA/cm2 for an equiv. thickness of only 2.75 μm. External quantum efficiency (EQE) measurements are in very good agreement with FDTD simulations. We infer an optical path enhancement of 10 in the long wavelength range. A simple propagation model reveals that the low photon escape probability of 25% is the key factor in the light trapping mechanism. The main limitations of our current technol. and the potential efficiencies achievable with contact optimization are discussed.
- 26Fountaine, K. T.; Cheng, W.-H.; Bukowsky, C. R.; Atwater, H. A. Near-Unity Unselective Absorption in Sparse InP Nanowire Arrays. ACS Photonics 2016, 3, 1826– 1832, DOI: 10.1021/acsphotonics.6b0034126https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFGrsrfK&md5=62c2353bc2a7a291c3607f9cc39c312bNear-Unity Unselective Absorption in Sparse InP Nanowire ArraysFountaine, Katherine T.; Cheng, Wen-Hui; Bukowsky, Colton R.; Atwater, Harry A.ACS Photonics (2016), 3 (10), 1826-1832CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)We exptl. demonstrate near-unity, unselective absorption, broadband, angle-insensitive, and polarization-independent absorption, in sparse InP nanowire arrays, embedded in flexible polymer sheets via geometric control of waveguide modes in two wire motifs: (i) arrays of tapered wires and (ii) arrays of nanowires with varying radii. Sparse arrays of these structures exhibit enhanced absorption due to strong coupling into the first order azimuthal waveguide modes of individual nanowires; wire radius thus controls the spectral region of the absorption enhancement. Whereas arrays of cylindrical wires with uniform radius exhibit narrowband absorption, arrays of tapered wires and arrays with multiple wire radii expand this spectral region and achieve broadband absorption enhancement. Herein, we present an economic, top-down lithog./etch fabrication method that enables fabrication of multiple InP nanowire arrays from a single InP wafer with deliberate control of nanowire radius and taper. Using this method, we create sparse tapered and multiradii InP nanowire arrays and demonstrate optical absorption that is broadband (450-900 nm), angle-insensitive, and near-unity (>90%) in roughly 100 nm planar equivalence of InP. These highly absorbing sparse nanowire arrays represent a promising approach to flexible, high efficiency optoelectronic devices, such as photodetectors, solar cells, and photoelectrochem. devices.
- 27Marko, G.; Prajapati, A.; Shalev, G. Subwavelength Nonimaging Light Concentrators for the Harvesting of the Solar Radiation. Nano Energy 2019, 61, 275– 283, DOI: 10.1016/j.nanoen.2019.04.08227https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXos12ht7g%253D&md5=9d0adfb318a5ecc78fccf7f23968dcebSubwavelength nonimaging light concentrators for the harvesting of the solar radiationMarko, Gilad; Prajapati, Ashish; Shalev, GilNano Energy (2019), 61 (), 275-283CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Light trapping and the broadband absorption of the solar radiation is of interest to various solar energy harvesting applications. In the current work, we report a new paradigm for light trapping, that is light trapping based on arrays of subwavelength nonimaging light concentrators (NLCs). We numerically show that silicon NLC arrays provide >75% broadband absorption enhancement of the solar radiation compared with that of optimized nanopillar arrays. The paper focuses on free-floating arrays of subwavelength compd. parabolic concentrators (henceforth CPC arrays) as a case study. The calcns. reveal that CPC arrays function as anti-transmission layers as only few photons transverse the CPC arrays which is in contrast to nanopillar arrays that function as anti-reflection layers. We show that the absorption enhancement in CPC arrays is due to efficient occupation of Mie modes which is motivated by the unique CPC geometry, and we demonstrate light trapping at the Yablonovitch limit. Finally, we examine the performance of a photovoltaic cell based on CPC arrays with respect to base doping levels and surface recombination. We show that the short-circuit c.d. of the CPC-based cell is >75% higher than the short-circuit c.d. of a photovoltaic cell based on optimized nanopillar arrays. We believe that light trapping based on NLC arrays paves the way to various applications such as ultra-thin photovoltaic cells.
- 28Prajapati, A.; Llobet, J.; Antunes, M.; Martins, S.; Fonseca, H.; Calaza, C.; Gaspar, J.; Shalev, G. An Efficient and Deterministic Photon Management Using Deep Subwavelength Features. Nano Energy 2020, 70, 104521, DOI: 10.1016/j.nanoen.2020.10452128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisVSqtbo%253D&md5=64f44e7a5fc9862f3499df09da94efacAn efficient and deterministic photon management using deep subwavelength featuresPrajapati, Ashish; Llobet, Jordi; Antunes, Mariana; Martins, Sofia; Fonseca, Helder; Calaza, Carlos; Gaspar, Joao; Shalev, GilNano Energy (2020), 70 (), 104521CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Light trapping and the broadband absorption of the solar radiation are significant to a plethora of absorption-based photonic devices. Specifically, efficient broadband absorption was recently demonstrated with arrays of subwavelength structures. The current study examines both numerically and exptl. light trapping driven by deep sidewall subwavelength structures (DSSS) in silicon nanopillar (NP) arrays (DSSS arrays). Particularly, the focus is on DSSS geometries that are an inherent outcome of the top-down dry etch approach used in arrays of high aspect ratio NPs due to the periodical operationality of the Bosch dry etch method. ∼10% enhancement in the broadband absorption of DSSS arrays compared with NP arrays is demonstrated numerically, as well as the generation of near-IR absorptivity peaks of ∼25% for DSSS arrays. Importantly, it is shown that the introduction of DSSS systematically blue-shifts the absorptivity peaks of the NP arrays and in this manner a deterministic light trapping is possible. Finally, decrements of ∼40% in direct reflectivity and ∼7% in diffused reflectivity in DSSS arrays realized on silicon wafers is demonstrated exptl.
- 29Yu, Z.; Raman, A.; Fan, S. Fundamental Limit of Light Trapping in Grating Structures. Opt. Express 2010, 18, A366– A380, DOI: 10.1364/oe.18.00a36629https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Skt7%252FL&md5=9a1bfbf29b02fbc51be2f0c104aa450fFundamental limit of light trapping in grating structuresYu, Zongfu; Raman, Aaswath; Fan, ShanhuiOptics Express (2010), 18 (S3), A366-A380CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n2, but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile's symmetry on the absorption enhancement limit. Numerical simulations are applied to support the theory. Our findings provide general guidance for the design of grating structures for light-trapping solar cells.
- 30Sturmberg, B. C. P.; Dossou, K. B.; Botten, L. C.; Asatryan, A. A.; Poulton, C. G.; de Sterke, C. M.; McPhedran, R. C. Modal Analysis of Enhanced Absorption in Silicon Nanowire Arrays. Opt. Express 2011, 19, A1067, DOI: 10.1364/OE.19.0A106730https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXht1Omsr7K&md5=4aa51b229eddb87b21e9c55b70147affModal analysis of enhanced absorption in silicon nanowire arraysSturmberg, Bjorn C. P.; Dossou, Kokou B.; Botten, Lindsay C.; Asatryan, Ara A.; Poulton, Christopher G.; Martijn de Sterke, C.; McPhedran, Ross C.Optics Express (2011), 19 (S5), A1067-A1081CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)We analyze the absorption of solar radiation by silicon nanowire arrays, which are being considered for photovoltaic applications. These structures have been shown to have enhanced absorption compared with thin films, however the mechanism responsible for this is not understood. Using a new, semi-analytic model, we show that the enhanced absorption can be attributed to a few modes of the array, which couple well to incident light, overlap well with the nanowires, and exhibit strong Fabry-Perot resonances. For some wavelengths the absorption is further enhanced by slow light effects. We study the evolution of these modes with wavelength to explain the various features of the absorption spectra, focusing first on a dil. array at normal incidence, before generalizing to a dense array and off-normal angles of incidence. The understanding developed will allow for optimization of simple SiNW arrays, as well as the development of more advanced designs.
- 31Chauhan, A.; Prajapati, A.; Calaza, C.; Fonseca, H.; Sousa, P. C.; Llobet, J.; Shalev, G. Near-Field Optical Excitations in Silicon Subwavelength Light Funnel Arrays for Broadband Absorption of the Solar Radiation. Sol. RRL 2021, 5, 2100721, DOI: 10.1002/solr.20210072131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXit1ygur3M&md5=847825689a8677636a2ff713929e9e0eNear-Field Optical Excitations in Silicon Subwavelength Light Funnel Arrays for Broadband Absorption of the Solar RadiationChauhan, Ankit; Prajapati, Ashish; Calaza, Carlos; Fonseca, Helder; Sousa, Patricia C.; Llobet, Jordi; Shalev, GilSolar RRL (2021), 5 (12), 2100721CODEN: SRORAW; ISSN:2367-198X. (Wiley-VCH Verlag GmbH & Co. KGaA)Broadband absorption is pivotal for the realization of green energy based on solar energy. Decoration of photovoltaic cells with arrays of subwavelength formations provides an efficient means for broadband absorption in thin films. Surface arrays of silicon light funnels (LFs) have been suggested as a promising platform to produce broadband absorption that is considerably superior to other subwavelength arrays such as the well-known nanopillar (NP) arrays. The current study explores the underlying mechanism of broadband absorption in LF arrays. To this end, the optical near-field of LF and NP arrays is exptl. probed using a near-field scanning optical microscopy. It is shown that in LF arrays the near-field increases as the array period decreases in contrast with NP arrays in which the near-field decreases with decreasing array period. Also, the exptl. near-field of the arrays follows the numerically calcd. absorption cross section of the array-nested NPs/LFs. Therefore, the origin to the broadband absorption in compact LF arrays is due to field overlap of adjacent LFs which increases the absorption cross section of the individual LFs composing the array. This absorption cross-sectional enhancement coupled with a higher filling ratio in compact arrays produces broadband absorption that is significantly greater than that of NP arrays.
- 32Chauhan, A.; Prajapati, A.; Llobet, J.; Fonseca, H.; Sousa, P. C.; Calaza, C.; Shalev, G. Incorporation of Nano-Features into Surface Photoactive Arrays for Broadband Absorption of the Solar Radiation. Sol. Energy Mater. Sol. Cells 2022, 245, 111864, DOI: 10.2139/ssrn.408958132https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xhslemsr7M&md5=49f1711278ce8fcae04de742796ac738Incorporation of nano-features into surface photoactive arrays for broadband absorption of the solar radiationChauhan, Ankit; Prajapati, Ashish; Llobet, Jordi; Fonseca, Helder; Sousa, Patricia C.; Calaza, Carlos; Shalev, GilSolar Energy Materials & Solar Cells (2022), 245 (), 111864CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)Surface arrays of photoactive materials with subwavelength dimensions are important for energy harvesting applications due to their capacity for broadband and omnidirectional absorption of the solar radiation. It was recently proposed and demonstrated that the absorption performance of such arrays can be further amplified with the introduction of addnl. nano-features. In the current work we consider the incorporation of nano-features into nanopillar (NP) arrays. The considered nano-features are: quasi-nanolenses, sidewall nano-decorations, and decreasing the NP bottom diam. to transform it into a light funnel (LF). The underlying various light trapping mechanisms are examd. using near-field microscopy. Near-field microscopy is used to obtained both high-resoln. far-field imaging, as well as mapping of the near-field photon distributions of the arrays. Firstly, it is shown that the main contribution to far-field reflected photons is from the ambient surrounding the silicon structures. Secondly, the incorporation of the various nano-features induces a decrease in the reflected far-field photons which originate from this ambient region. Also, it is shown how the incorporation of quasi-nanolenses concludes a decrease in far-field photons reflected in the oblique directions with high polar angles, whereas the incorporation of sidewall nano-decorations leads to a decrease in far-field photons reflected in directions of small polar angles. Also, the incorporation of both qNL and sidewall nano-decorations is examd., and light trapping with the LF geometry is discussed and demonstrated. Finally, understanding the underlying light trapping mechanisms will support the deterministic design of subwavelength arrays incorporated with nano-features for efficient harvesting of the solar radiation.
- 33Oh, J.; Yuan, H.-C.; Branz, H. M. An 18.2%-Efficient Black-Silicon Solar Cell Achieved through Control of Carrier Recombination in Nanostructures. Nat. Nanotechnol. 2012, 7, 743– 748, DOI: 10.1038/nnano.2012.16633https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVaqur7N&md5=dee4dd39adb901a862bd817a1aa6e539An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructuresOh, Jihun; Yuan, Hao-Chih; Branz, Howard M.Nature Nanotechnology (2012), 7 (11), 743-748CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Silicon nanowire and nanopore arrays promise to reduce manufg. costs and increase the power conversion efficiency of photovoltaic devices. So far, however, photovoltaic cells based on nanostructured silicon exhibit lower power conversion efficiencies than conventional cells due to the enhanced photocarrier recombination assocd. with the nanostructures. Here, surface recombination and Auger recombination in wafer-based nanostructured silicon solar cells are identified and sep. measured. By identifying the regimes of junction doping concn. in which each mechanism dominates, it is possible to design and fabricate an independently confirm 18.2%-efficient nanostructured black-silicon' cell that does not need the antireflection coating layer(s) normally required to reach a comparable performance level. The results suggest design rules for efficient high-surface-area solar cells with nano- and microstructured semiconductor absorbers.
- 34Leutz, R.; Suzuki, A. Nonimaging Fresnel Lenses; Springer Berlin, Heidelberg: Berlin Heidelberg, 2001.There is no corresponding record for this reference.
- 35Miller, D. C.; Kurtz, S. R. Durability of Fresnel lenses: A review specific to the concentrating photovoltaic application. Sol. Energy Mater. Sol. Cells 2011, 95, 2037– 2068, DOI: 10.1016/j.solmat.2011.01.03135https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntlWrsL8%253D&md5=4bc1ac7e5af64a6c814123469897eaa5Durability of Fresnel lenses: A review specific to the concentrating photovoltaic applicationMiller, David C.; Kurtz, Sarah R.Solar Energy Materials & Solar Cells (2011), 95 (8), 2037-2068CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)A review. The durability of Fresnel lenses used in the concg. photovoltaic (CPV) application is reviewed from the literature. The examn. here primarily concerns monolithic lenses constructed of poly(Me methacrylate) (PMMA), with supplemental examn. of silicone-on-glass (SOG) composite lenses. For PMMA, the review includes the topics of: optical durability (loss of transmittance with age); discoloration (the wavelength-specific loss of transmittance); microcrazing and hazing; fracture and mech. fatigue; phys. aging, creep, shape change, buckling, and warping; and solid erosion. Soiling, or the accumulation of particulate matter, is examd. in the following contexts: its magnitude of redn. in transmittance; variation with time, module tilt, and wavelength; the processes of adhesion and accumulation; particle size, distribution, compn., and morphol.; and its prevention. Photodegrdn. and thermal decompn., mechanisms enabling aging, are examd. relative to the CPV-specific environment. VAspects specific to SOG lenses include: solarization of the glass superstrate; corrosion of glass; delamination of the silicone/glass interface; change in focus due to thermal misfit between the laminate layers; and the chem. stability of poly(dimethylsiloxane) (PDMS). Recommendations for future research are provided, based on the most important and the least explored topics.
- 36Xie, W. T.; Dai, Y.; Wang, R. Z.; Sumathy, K. Concentrated Solar Energy Applications Using Fresnel Lenses : A Review. Renewable Sustainable Energy Rev. 2011, 15, 2588– 2606, DOI: 10.1016/j.rser.2011.03.031There is no corresponding record for this reference.
- 37Sze, S. M. Physics of Semiconductor Devices, 2nd ed.; Wiley: New York, 1981.There is no corresponding record for this reference.
- 38Lochmann, W.; Haug, A. Phonon-assisted Auger recombination in Si with direct calculation of the overlap integrals. Solid State Commun. 1980, 35, 553– 556, DOI: 10.1016/0038-1098(80)90896-038https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXlvFKgtLg%253D&md5=6e8fade9aeae8fa1fc5dd5e2096d8e44Phonon-assisted Auger recombination in silicon with direct calculation of the overlap integralsLochmann, W.; Haug, A.Solid State Communications (1980), 35 (7), 553-6CODEN: SSCOA4; ISSN:0038-1098.The overlap integrals are calcd for Si by means of the full zone double group k.p-method whereas they are usually roughly estd. The results confirm that phonon-assisted Auger recombination is the predominating radiationless recombination mechanism in indirect band gap semiconductors. This holds not only for highly doped materials but also for electron-hole drops.
- 39Green, M. A.; Keevers, M. J. Optical Properties of Intrinsic Silicon at 300 K. Prog. Photovoltaics Res. Appl. 1995, 3, 189– 192, DOI: 10.1002/pip.467003030339https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXnvVakuro%253D&md5=2e3aabe5a0d717ba06aaec6c811e2d19Optical properties of intrinsic silicon at 300 KGreen, Martin A.; Keevers, Mark J.Progress in Photovoltaics (1995), 3 (3), 189-92CODEN: PPHOED; ISSN:1062-7995. (Wiley)An updated tabulation is presented of the optical properties of intrinsic silicon relevant to solar cell calcns. The absorption coeff., refractive index, and extinction coeff. at 300 K are tabulated over the 0.25-1.45 μm wavelength range at 0.01 μm intervals.
- 40Hoex, B.; Heil, S. B. S.; Langereis, E.; van de Sanden, M. C. M.; Kessels, W. M. M. Ultralow Surface Recombination of C-Si Substrates Passivated by Plasma-Assisted Atomic Layer Deposited Al2O3. Appl. Phys. Lett. 2006, 89, 042112, DOI: 10.1063/1.224073640https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XotFSmtb4%253D&md5=4935f3e06ded9894a3e74433076321d6Ultralow surface recombination of c-Si substrates passivated by plasma-assisted atomic layer deposited Al2O3Hoex, B.; Heil, S. B. S.; Langereis, E.; van de Sanden, M. C. M.; Kessels, W. M. M.Applied Physics Letters (2006), 89 (4), 042112/1-042112/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Excellent surface passivation of c-Si has been achieved by Al2O3 films prepd. by plasma-assisted at. layer deposition, yielding effective surface recombination velocities of 2 and 13 cm/s on low resistivity n- and p-type c-Si, resp. These results obtained for ∼30 nm thick Al2O3 films are comparable to state-of-the-art results when employing thermal oxide as used in record-efficiency c-Si solar cells. A 7 nm thin Al2O3 film still yields an effective surface recombination velocity of 5 cm/s on n-type silicon.