Dependence of photocurrent generation on the crystalline phase of titanyl phthalocyanine film in heterojunction photovoltaic cells

Abstract

We report that the photocurrent generation of a titanyl phthalocyanine (TiOPc) layer in heterojunction photovoltaic cells is strongly dependent on the crystalline phase of the TiOPc layer. Vacuum-deposited TiOPc films with an amorphous phase were changed into mixed crystalline films with two or three crystalline phases, Phase I and Phase II or Phase Y, by solvent vapor treatment with various solvents, which is confirmed from the ultraviolet–visible absorption spectra and X-ray diffraction patterns of solvent-vapor-treated TiOPc films. From the incident photon to current conversion efficiency (IPCE) measurement, it is clearly demonstrated that only the amorphous phase and Phase II but not Phase I nor Phase Y of TiOPc can contribute to photoelectric conversion in heterojunction photovoltaic cells. This result may come from the low charge generation (exciton dissociation) efficiency of Phase I and Phase Y crystalline structures, which was supported by the change in IPCE curves under inverse bias application.