Back contact band offset study of Mo-CZTS based solar cell structure by using XPS/UPS techniques

Abstract

The back contact issues of Cu2ZnSnS4 (CZTS) solar cells are rarely studied. The conventional back contact layers used for CZTS are molybdenum (Mo) and moly-disulfide (MoS2). In this paper, the band offset at the Mo/MoS2 interface is reported. The Mo/MoS2 interface was formed by annealing Mo foil in a sulfur rich ambient. XPS/UPS spectra were then obtained without exposing the sample to ambient atmosphere. The valence band maxima (VBM) and the core level binding energies were obtained to estimate the band alignment. Our results showed that a Schottky junction was formed at the Mo/MoS2 interface with a barrier height of 0.36eV. The valence band maximum at the interface was 0.84eV and the corresponding band bending was 0.11 eV at the interface. A band diagram of the Mo/MoS2 interface created with these values showed that the formation of MoS2 between Mo and CZTS layer would not be a barrier to the holes at least at the Mo-side of the Mo/MoS2/CZTS interface.