Energy level alignment in TiO2/metal sulfide/polymer interfaces for solar cell applications

Abstract

Semiconductor sensitized solar cell interfaces have been studied with photoelectron spectroscopy to understand the interfacial electronic structures. In particular, the experimental energy level alignment has been determined for complete TiO₂/metal sulfide/polymer interfaces. For the metal sulfides CdS, Sb₂S₃ and Bi₂S₃ deposited from single source metal xanthate precursors, it was shown that both driving forces for electron injection into TiO₂ and hole transfer to the polymer decrease for narrower bandgaps. The energy level alignment results were used in the discussion of the function of solar cells with the same metal sulfides as light absorbers. For example Sb₂S₃ showed the most favourable energy level alignment with 0.3 eV driving force for electron injection and 0.4 eV driving force for hole transfer and also the most efficient solar cells due to high photocurrent generation. The energy level alignment of the TiO₂/Bi₂S₃ interface on the other hand showed no driving force for electron injection to TiO₂, and the performance of the corresponding solar cell was very low.