Regulation of hydrothermal reaction kinetics with sodium sulfide for certified 10.7% efficiency Sb2(S,Se)3 solar cells

Abstract Antimony chalcogenide (Sb 2 (S,Se) 3 ) is a promising candidate for next-generation photovoltaic materials due to its optoelectronic properties, high absorption coefficient and material availability. Hydrothermal deposition has advanced the technology, but there is a limited understanding of the underlying reaction mechanisms, often resulting in non-ideal valence band maximum gradient across the absorber thickness and high concentration of deep-level defects. Here we introduce sodium sulfide as an additive in the precursor solution to control reaction kinetics. This strategy enables a more uniform depth-dependent elemental distribution, flattens the unfavourable valence band maximum gradient across the depth and suppresses the formation of deep-level defects. We demonstrate an improvement in Sb 2 (S,Se) 3 material quality, achieving a power conversion efficiency of 11.02%, with a certified value of 10.7 ± 0.37%. This work advances the efficiency for Sb 2 (S,Se) 3 solar cells and provides insights to optimize the hydrothermal synthesis for this technology.