Photovoltaic properties of WSe2 single crystals studied by photoelectron spectroscopy

Abstract Different surfaces and Schottky barriers of WSe 2 single crystals have been investigated with photoelectron spectroscopy using synchrotron radiation. An acceptor level with E A − E V =0.45 eV, known from the literature as an important defect level in WSe 2 , is identified and attributed to the non-van der Waals planes. The photovoltages obtained for the Schottky barriers prepared on UHV-cleaved selenium grown p-WSe 2 single crystals depend on the lateral conductivity of the surface which is a function of metal-film thickness and morphology. Increased lateral conductivity leads to smaller photovoltages indicating laterally inhomogeneous losses of photoexcited carriers. It is suggested that the crystal quality of WSe 2 single crystals, and thus, achievable conversion efficiencies of WSe 2 solar cells, is strongly dependent on the transport agent used in chemical vapor transport growth.