Sputtering of Molybdenum as a Promising Back Electrode Candidate for Superstrate Structured Sb₂ S₃ Solar Cells

Sb₂ S₃ is rapidly developed as light absorber material for solar cells due to its excellent photoelectric properties. However, the use of the organic hole transport layer of Spiro-OMeTAD and gold (Au) in Sb₂ S₃ solar cells imposes serious problems in stability and cost. In this work, low-cost molybdenum (Mo) prepared by magnetron sputtering is demonstrated to serve as a back electrode in superstrate structured Sb₂ S₃ solar cells for the first time. And a multifunctional layer of Se is inserted between Sb₂ S₃ /Mo interface by evaporation, which plays vital roles as: i) soft loading of high-energy Mo particles with the help of cottonlike-Se layer; ii) formation of surficial Sb₂ Se₃ on Sb₂ S₃ layer, and then reducing hole transportation barrier. To further alleviate the roll-over effect, a pre-selenide Mo target and consequentially form a MoSe₂ is skillfully sputtered, which is expected to manipulate the band alignment and render an enhanced holes extraction. Impressively, the device with an optimized Mo electrode achieves an efficiency of 5.1%, which is one of the highest values among non-noble metal electrode based Sb₂ S₃ solar cells. This work sheds light on the potential development of low-cost metal electrodes for superstrate Sb₂ S₃ devices by carefully designing the back contact interface.