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

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(0.7)MA(0.3)Pb(0.5)Sn(0.5)I(3) precursor solution to improve device performance. Incorporation of AHPD into the FA(0.7)MA(0.3)Pb(0.5)Sn(0.5)I(3) 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.