Bifunctional additive 2-amino-3-hydroxypyridine for stable and high-efficiency tin–lead perovskite solar cells

Abstract

Tin–lead (Sn–Pb) mixed perovskite has received widespread attention due to its suitable band gap width and high optical absorption coefficients. However, the power conversion efficiency (PCE) of Sn–Pb mixed perovskite solar cells (PSCs) is still low due to the fact that Sn²⁺ could be easily oxidized to Sn⁴⁺ and an excessively rapid crystallization rate was observed for the Sn–Pb mixed perovskite materials. Herein, we introduced 2-amino-3-hydroxypyridine (AHPD), which contains a pyridine nitrogen and an –NH₂ group in the molecule, as a bidentate anchoring additive in the FA_0.7MA_0.3Pb_0.5Sn_0.5I₃ precursor solution to improve device performance. Incorporation of AHPD into the FA_0.7MA_0.3Pb_0.5Sn_0.5I₃ precursor solution was found to effectively suppress the Sn²⁺ oxidation and thus the p-doping level defects. Furthermore, the pyridine nitrogen and the enamine-like –NH₂ could retard the nucleation and crystallization rate by forming a coordinating interaction with PbI₂/SnI₂, forming compact large-grained films and also improving the carrier transport by passivation of the grain boundaries. Overall, compared with the control device (a PCE of 15.72%), an optimized device incorporating 2 mol% AHPD exhibited a PCE of 19.18% for narrow band gap perovskite solar cells, an increase of nearly 22%, with a high level of reproducibility.