4‐Hydrazinobenzoic‐acid Antioxidant for High‐Efficiency Sn–Pb Alloyed Perovskite Solar Cells

Partial tin replacement of lead is expected to be an effective means to fine‐tune the bandgap of Sn–Pb alloyed lead‐halide perovskite to harvest near‐infrared light and thus further increase the efficiency of solar cells based on it, in particular for use as a bottom component cell in the tandem cell design to break through the theoretical Shockley–Queisser (S–Q) limit of the single‐junction solar cells. However, the efficiency of Sn–Pb alloyed perovskite solar cells (PSCs) is still lower than expected owing to the easy oxidation of Sn2+. Herein, a reducing agent 4‐hydrazinobenzoic acid is developed as an additive to suppress the oxidation of Sn2+ and, meanwhile, passivate surface defects. It is found that the optoelectronic performance of Sn–Pb alloyed perovskites is improved as evidenced by the mitigated trap state density and suppressed nonradiative recombination. As a result, the Sn–Pb alloyed PSC efficiency is increased to 21.09%, one of the highest for cells with this bandgap. It is expected that this method is applicable for general Sn–Pb‐based perovskite optoelectronics.