Received June 4, 2007

Revised Manuscript Received November 30, 2007

Abstract:

A novel series of white light emitting single polymers are prepared by incorporating low contents of quinacridone into the main chain of polyfluorene. This is the first report of quinacridone-containing conjugated polymer. Single layer devices (ITO/PEDOT:PSS/polymer/Ca/Al) are fabricated with these polymers. Energy transfer from fluorene segments to quinacridone unit is observed. Moreover, in the EL process, quinacridone unit can trap electrons and cannot trap holes from fluorene segments. Electroluminescence (EL) spectra of these polymers exhibit simultaneous blue emission (_max = 425 nm/445 nm) from the fluorene segments and yellow emission (_max = 540 nm/580 nm) from the quinacridone unit. The latter one comes from the partial energy transfer and charge trapping from the fluorene segments to the quinacridone unit. With the increase of the quinacridone unit's content in the copolymers, the relative intensity of the orange emission band in the EL spectra becomes stronger owing to the more complete energy transfer and charge trapping. For the polymer (PFQA3) with the quinacridone unit's content of 0.03 mol %, its EL spectrum shows balanced intensities of blue emission and orange emission, leading to white emission with CIE coordinates of (0.27, 0.35). Single layer device of this polymer exhibits the turn-on voltage of 3.5 V, luminous efficiency of 3.47 cd/A, power efficiency of 2.18 lm/W, external quantum efficiency of 1.33% and maximum brightness of 9062 cd/m². Increase of the quinacridone unit's content results in increased turn-on voltages and decreased EL efficiencies of the resulting devices owing to the serious trap of electrons by quinacridone unit and exciton quenching of quinacridone unit at high concentration, respectively.

Download the full text: PDF | HTML