Surface Chemical State Regulation via Bromine Methanol Etching for Efficient Antimony Selenide Solar Cells

Resistive impurities, such as antimony oxide and free elemental selenium, are present on the surface of antimony selenide (Sb 2 Se 3 ) films, which increase the series resistance of the devices. Developing surface chemical engineering to remove these impurities and improve the ohmic contact at the back interface is critical for enhancing device performance. In this study, we developed a chemical etching strategy using a corrosive bromine methanol (BM) solution to selectively remove detrimental impurity phases in Sb 2 Se 3 films, thereby improving their optoelectronic properties. The BM etching preferentially removes antimony oxide (Sb 2 O 3 ) and elemental selenium impurities from the surface of Sb 2 Se 3 films. Subsequently, bromide ions penetrate the bulk film along the grain boundaries of Sb 2 Se 3, enabling deep etching of impurity phases. Furthermore, this surface etching optimizes the energy level structure of Sb 2 Se 3, forming a favorable band alignment with the work function of the gold electrode. By this means, we achieved a power conversion efficiency (PCE) of 7.89%, which is the highest efficiency reported for hole-transport layer-free Sb 2 Se 3 solar cells so far. This study provides a useful and convenient approach to improve the quality of the absorber layer and the back contact for inorganic thin-film solar cells.