Mixed tin-lead perovskites with balanced crystallization and oxidation barrier for all-perovskite tandem solar cells

Mixed tin-lead perovskite solar cells have driven a lot of passion for research because of their vital role in all-perovskite tandem solar cells, which hold the potential for achieving higher efficiencies compared to single-junction counterparts. However, the pronounced disparity in crystallization processes between tin-based perovskites and lead-based perovskites, coupled with the easy Sn2+ oxidation, has long been a dominant factor contributing to high defect densities. In this study, we propose a multidimensional strategy to achieve efficient tin-lead perovskite solar cells by employing a functional N-(carboxypheny)guanidine hydrochloride molecule. The tailored N-(carboxypheny)guanidine hydrochloride molecule plays a pivotal role in manipulating the crystallization and grain growth of tin-lead perovskites, while also serving as a preservative to effectively inhibit Sn2+ oxidation, owing to the strong binding between N-(carboxypheny)guanidine hydrochloride and tin (II) iodide and the elevated energy barriers for oxidation. Consequently, single-junction tin-lead cells exhibit a stabilized power conversion efficiency of 23.11% and can maintain 97.45% of their initial value even after 3500 h of shelf storage in an inert atmosphere without encapsulation. We further integrate tin-lead perovskites into two-terminal monolithic all-perovskite tandem cells, delivering a certified efficiency of 27.35%. The disparity in crystallization processes between tin- and lead-based perovskites has been a dominant factor contributing to high defect densities. Here, authors employ a functional molecule to inhibit tin oxidation, realizing monolithic all-perovskite tandems with certified efficiency over 27%.