Lowest Open‐Circuit Voltage Deficit Achievement to Attain High Efficient Antimony Selenosulfide Solar Cells

Abstract Antimony selenosulfide (Sb 2 (S,Se) 3 ) solar cells bear great potential for sustainable photovoltaic technology, attributed to their excellent semiconductor properties. Despite the encouraging breakthroughs, the efficiency of Sb 2 (S,Se) 3 solar cells still leaves much room for improvement due to the large open‐circuit voltage (V OC ) deficit (the radiative V OC limit minus the high V OC ). Herein, ammonium sulfide ((NH 4 ) 2 S) solution is utilized to treat Sb 2 (S,Se) 3 films to tailor their surface properties. The disappearance of the hole defect (H1) and the decrease of the defect concentration of hole defect (H2) confirm that non‐radiative recombination is suppressed greatly. Photovoltage decay lifetime is greatly increases from 67.9 to 297.9 µs. The upshifted valence band maximum optimizes the energy level alignment between the p–n heterojunction, enhancing the carrier transport. Remarkably, this treatment yields a record lowest V OC deficit of 0.49 V by now, and the best device with 10.41% efficiency, ca. 25% improvement over the control device (8.35%). This study provides valuable insight into reducing the V OC deficit in solar cells and related photoelectronic devices by minimizing non‐radiative recombination, and also presents a great potential strategy to achieve the lowest V OC deficit.