Structural, optoelectronic and magnetic characterization of Cu2MnSnS4 thin films and correlation with photovoltaic performances

Cu2MnSnS4 (CMTS) is regarded as an emerging absorber for thin-film photovoltaic (PV) devices. In this work, CMTS thin films prepared using a low-cost, straightforward solution-based technique were extensively characterized, and the results were correlated with the preparation conditions and corresponding PV performances. X-ray diffraction techniques have been used to study crystallographic structure and microstructural parameters, while energetic band positions were depicted exploiting photoelectron yield spectroscopy and Kelvin probe measurements. The importance of fine-tuning the composition of the starting solution and the beneficial effect of post-deposition treatments were consequently highlighted. A strategy of slow cooling after annealing was studied, resulting in a new record for wet-prepared CMTS, with a champion device yielding 0.97% efficiency 5 months after the first PV measurement. Factors responsible for the typical modest efficiencies of CMTS have been investigated: photoluminescence revealed the presence of intra-gap defects, magnetic characterization revealed room-temperature short-range magnetic ordering, and electrical transport and thermal measurements highlighted a semimetallic-like character, all of which are barriers to achieving high PV performance in CMTS-based devices. Moreover, magnetometry indicates a weakly ordered spin-glass-like state, providing insight into the electronic correlations underlying the observed transport behavior.