Back Contact Plasma Treatment Enables 14.5% Efficient Solution‐Processed CuIn(S,Se)₂ Solar Cells

Abstract

Solution‐processed chalcopyrite thin film solar cells have made great progress but still lag behind the vacuum‐based ones due to inferior absorber quality and non‐ideal interfaces. Here, plasma treatment of the molybdenum (Mo) substrate is reported to modify the back interface and improve the efficiency of solution‐processed copper indium sulfoselenide (CuIn(S,Se)2, CISSe) solar cells. The results show plasma treatment oxides the surface Mo/MoO2 to high oxidation oxides MoO3‐x (0 ≤ x < 1). The higher surface polarity greatly improves the wettability of the substrate to the precursor solution and results in formation of more compact and uniform precursor film, which grows to void‐free larger grains absorber film with better adhesion to the substrate. In addition, the much higher chemical stability of MoO3‐x than Mo significantly reduces the thickness of high resistive MoSe2 layer. The improved absorber quality and back interface property decreases charge carrier recombination in the absorber and back contact interface, resulting in 14.53% efficiency solution‐processed CISSe solar cell, which is improved by 13% compared to device without plasma treatment.