Characterization of Organic p/n Junction Photodiodes Based on Poly(alkylthiophene)/Perylene Diimide Bilayers

Abstract

Photoconduction of bilayer organic p/n junction photocells can be finely tuned through the alteration of either the side chain orientation (regiorandom vs regioregular) or main chain structure in poly(3-alkylthiophene)s (P3ATs), where the incorporation of an electron-donating group (EDOT) appears to be an excellent method for enhancing the photoconduction. Moreover, doping of P3ATs proved to be an equally viable route for tuning the device characteristics. These polymers were used to fabricate bilayer organic photocells with the polymer as the p-type layer and 1,2-diaminobenzene perylene-3,4,9,10-tetracarboxylic acid diimide (PV) as the n-type layer. Action spectra at steady-state illumination demonstrated that all the interfaces (organic−organic p/n junction and organic−electrode) are actively involved in the photogeneration of carriers. Experiments showed that critical device properties, for example, open-circuit voltage (Voc) and short-circuit current (Isc), are not only dependent on the selection of electrodes and organic materials but also greatly affected by the illumination wavelength and intensity.