Selection of phenyl hydrazine derivatives as an Sn4+ reductant for tin–lead perovskite solar cells

Abstract

Hydrazine derivatives have been extensively studied as some of the earliest reductants for Sn–Pb mixed perovskite precursors. However, phenyl hydrazine (BH) as a strong reductant for Sn-based perovskite solutions has not been reported yet, and Sn²⁺ is unusually oxidized in the precursor solution with BH additives in our experiment. Thus, not all organic reductants are suitable as additives, and therefore selecting a suitable reductant should be paid special attention to. Herein, it is found that BH as a Brønsted base deprotonates MA⁺ to produce HI, which further catalyzes the oxidation of Sn²⁺ by DMSO. As an alternative, hydrochloride phenyl hydrazine with a sulfonic amide group (–SO₂–NH₂) is added to the precursor as a reductant and passivator. As a result, a power conversion efficiency of 22.01% is achieved, and prolonged shelf stability is realized.