Cu2ZnSnS4 films prepared by a hybrid PVD deposition system: a multi-layered graphitic carbon intermediate layer at the Mo/CZTS interface

Abstract

We report the insertion of a new intermediate layer, a multi-layered graphitic carbon (MLGC), at Mo/CZTS interface and its impact on the structural and morphological characteristics of the back interface and absorber. MLGC was synthesized directly on Mo-coated SLG under a gas mixture flow of H₂/CH₄ at 550 °C via PECVD for 3 and 5 h. CZTS precursors were prepared on SLG/Mo and MLGC-coated SLG/Mo in a hybrid physical vapor deposition system, including evaporation and sputtering techniques, then subjected to sulfurization at 550 °C. The sheet resistance of back contact, microstructural parameters of the absorbers, the distributions of C and constituent elements were investigated. The diffraction peaks of the hexagonal Mo₂C indicated the reaction between the C and Mo before the MLGC’s growth. Raman analysis confirmed the formation of the MLGC during the long deposition time after the Mo₂C formation. With the addition of MLGC, the sheet resistance of the back contact decreased from 2 to 0.5 Ω/sq, and the crystallite size of the absorbers improved. Raman spectra from the interface exhibited that MoS₂ peaks’ intensities significantly reduced with increasing the growth time. This implied that the 5 h-deposited MLGC was more effective in blocking the reaction between Mo and S. The absorbers with the MLGC had more uniform surface morphologies, densely packed grains, and fewer secondary phases. FIB analysis revealed the separation of the absorber with the 5 h-deposited MLGC into two parts due to C impurity. More C diffusion into the absorber for this sample was confirmed by SIMS.