Web Release Date: October 24,
Self-Assembled Hybrid Polymer-TiO2 Nanotube Array Heterojunction Solar Cells
Department of Electrical Engineering and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802
Received July 9, 2007
In Final Form: September 17, 2007
Abstract:
Films comprised of 4 
m long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene
glycol based electrolyte. A carboxylated polythiophene derivative was self-assembled onto the TiO2 nanotube arrays
by immersing them in a solution of the polymer. The binding sites of the carboxylate moiety along the polymer chain
provide multiple anchoring sites to the substrate, making for a stable rugged film. Backside illuminated liquid junction
solar cells based on TiO2 nanotube films sensitized by the self-assembled polymeric layer showed a short-circuit
current density of 5.5 mA cm-2, a 0.7 V open circuit potential, and a 0.55 fill factor yielding power conversion
efficiencies of 2.1% under AM 1.5 sun. A backside illuminated single heterojunction solid state solar cell using the
same self-assembled polymer was demonstrated and yielded a photocurrent density as high as 2.0 mA cm-2. When
a double heterojunction was formed by infiltrating a blend of poly(3-hexylthiophene) (P3HT) and C60-methanofullerene
into the self-assembled polymer coated nanotube arrays, a photocurrent as high as 6.5 mA cm-2 was obtained under
AM 1.5 sun with a corresponding efficiency of 1%. The photocurrent action spectra showed a maximum incident
photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25% for the single heterojunction
solid state solar cells.
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