Overcoming Limitations in Water-Ethanol Sprayed Superstrate Solar Cells by Compositional Engineering of Cu 2 CdSn(S,Se) 4 .

The increasing demand for solar energy requires materials from earth-abundant elements to ensure cost-effective production. One such light harvester Cu 2 CdSn(S,Se) 4 fulfills this property. We report the development of functional solar cells based on Cu 2 CdSn(S,Se) 4 , which has been previously unreported. Furthermore, we deposited the thin films of Cu 2 CdSn(S,Se) 4 by spray pyrolysis using environmentally benign solvents, in a superstrate architecture, reducing the potential cost of upscaling, the environmental hazards, and enabling its use in semitransparent or tandem solar cells. We analyze the Cu 2 CdSn(S,Se) 4 and its optoelectronic characteristics with different sulfur and selenium ratios in the composition. We noted that Se is homogeneously distributed in the absorber and electron transport layer, forming a Cd(S,Se) phase that impacts the optoelectronic properties. The introduction of Se, up to 30%, is found to have a positive impact on the solar cell performance, largely improving the fill factor and absorption in the infrared region, while the voltage deficit is reduced. The device with a Cu 2 CdSn(S 2.8 Se 1.2 ) composition had a 3.5% solar-to-electric conversion efficiency, which is on par with the reported values for chalcogenides and the first report using Cu 2 CdSn(S,Se) 4 . We identified the critical factors that limit the efficiency, revealing pathways to further reduce the losses and improve the performance. This work provides the first proof of concept of a novel material, paving the way for developing cost-efficient solar cells based on earth-abundant materials.