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

The manganese-based quaternary chalcogenide Cu2MnSnS4 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 Cu2MnSnS4 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. Cu2MnSnS4 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 (η = 0.92 %) for wet-synthesised Cu2MnSnS4 was reached. Since the photovoltaic performances were poor despite the high quality of Cu2MnSnS4 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 Cu2MnSnS4 surface, and that band alignment between Cu2MnSnS4 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.