Low-bandgap mixed tin-lead (Sn-Pb) perovskites are promising near-infrared absorbers for all-perovskite tandem solar cells (APTSCs), but suffer from Sn-related defects, ion migration, and poor crystallinity. Herein, we developed a synergistic dual-molecule additive strategy by incorporating aminoguanidine sulfate (AGS) and L-alanine hydrochloride (AHC) into the Sn-Pb perovskite precursor. The guanidine moieties of AGS bonded to Sn vacancies to inhibit the oxidation of Sn2+ and formed hydrogen bonds with formamidinium (FA+) to immobilize its migration. Besides, the ionic hydrogen bonds between AHC and the perovskite components slowed down the crystallization process of perovskite and inhibited halide ion migration. Importantly, the specific interaction between AGS and AHC enabled a uniform distribution of the additives and provided efficient defect passivation at grain boundaries. This synergy regulated the film formation kinetics, promoted preferred orientation growth, and enhanced crystallinity, thereby reducing non-radiative recombination and ion migration. As a result, our Sn-Pb perovskite solar cells achieved an efficiency of up to 23.44%. Furthermore, we demonstrated a champion efficiency of 29.36% (certified 28.57%) for APTSCs.
You et al. (Thu,) studied this question.