Is indium tin oxide a suitable electrode in organic solar cells?: Photovoltaic properties of interfaces in organic p/n junction photodiodes

The charge generation properties at all interfaces of a p/n junction, bilayer photodiode have been investigated by means of the photoaction spectrum (PAS) as a function of applied bias. The organic photodiode was fabricated with a low-glass transition temperature (T-g) polysiloxane with pendant hydrazone groups as the p-type material and a perylene diimide derivative as the n-type material. The PAS under short circuit and reverse bias showed an antibatic response at the high-energy region (3.0-3.5 eV), and a symbatic response at the low-energy region (2.0-3.0 eV). However, under forward bias, the PAS showed the opposite behavior. These results are interpreted in terms of the band structure of tin-doped indium oxide (ITO) that prevents effective photoinjection of electrons at the polymer/ITO interface and the relative energy levels of the constituent materials. (c) 2006 American Institute of Physics.