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

Abstract

The charge generation properties at all interfaces of a p/np∕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 (Tg)(Tg) polysiloxane with pendant hydrazone groups as the pp-type material and a perylene diimide derivative as the nn-type material. The PAS under short circuit and reverse bias showed an antibatic response at the high-energy region (3.0–3.5 eV)(3.0–3.5eV), and a symbatic response at the low-energy region (2.0–3.0 eV)(2.0–3.0eV). 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.