Wet synthesis of Cu2MnSnS4 thin films for photovoltaics: Oxidation control and CdS impact on device performances

The manganese-based quaternary chalcogenide Cu 2 MnSnS 4 could have the chance to promote the production of sustainable solar cells, but the reported photovoltaic efficiencies are still too poor to push the research on the topic. Herein, a low-cost, straightforward, and sustainable wet methodology to synthesise Cu 2 MnSnS 4 thin films is reported. The main issues that hindered their power conversion efficiencies have been investigated. Firstly, the manganese oxidation state has been stabilised by fine-tuning the synthesis parameters. Cu 2 MnSnS 4 was obtained in the crystalline structure of stannite, and no oxygen was found in the material bulk. Prototype devices in substrate configuration were produced, and the new record efficiency ( eta = 0.92 %) for wet-synthesised Cu 2 MnSnS 4 was reached. Since the photovoltaic performances were poor despite the high quality of Cu 2 MnSnS 4 produced, the interface between the light absorber material and the buffer layer, CdS, was investigated, and its suitability to work as an efficient photovoltaic p-n junction was evaluated. We reveal that the buffer layer deposition procedure highly impacts the composition of the Cu 2 MnSnS 4 surface, and that band alignment between Cu 2 MnSnS 4 and CdS is unfavourable. The statements have been sustained by X-ray diffraction and Raman analysis, X-ray and ultraviolet photoelectron, electron paramagnetic resonance, and energy dispersive X-ray spectroscopies.