Bimolecular Crystallization Modulation Boosts the Efficiency and Stability of Methylammonium-Free Tin-Lead Perovskite and All-Perovskite Tandem Solar Cells

The elimination of methylammonium (MA) cation from mixed tin-lead (Sn-Pb) narrow-bandgap (NBG) perovskites is an effective approach to enhance the operational stability of all-perovskite tandem solar cells (TSCs). Unfortunately, the uncontrolled nucleation and crystallization processes of MA-free Sn-Pb perovskites usually lead to inferior film quality and device performance. Herein, a bimolecular crystallization modulation strategy is reported by using guanidine thiocyanate (GuaSCN) and aminoacetamide hydrochloride (AHC) together as additives to improve the film quality of MA-free Sn-Pb perovskites. It is demonstrated that the use of bimolecular additives can effectively improve the crystallinity, increase the grain size, and induce a preferred (100) orientation for the corresponding films, leading to high-quality absorber with considerably reduced defect density and suppressed non-radiative recombination. In addition, the bimolecular additives can reduce the self-p-doping hole concentration within the perovskite films and enhance the charge extraction at the perovskite/electron transport layer interface. The modified NBG perovskite solar cells deliver a power conversion efficiency (PCE) of 22.14%. Coupled with the wide-bandgap (WBG) subcell, the all-perovskite TSCs give a champion certified PCE of 27.15%, which is the highest certified PCE for MA-free all-perovskite TSCs. Encapsulated tandem devices maintain 90% of the initial PCE after 473 h operation. In this study, a bimolecular crystallization modulation strategy by using guanidine thiocyanate and aminoacetamide hydrochloride together as additives to improve the film quality of methylammonium-free Sn-Pb perovskites, which allows to fabricate Sn-Pb perovskite solar cells and all-perovskite tandem cells with encouraging efficiencies of 22.14% and 27.41%, respectively. image