Boosting All‐Perovskite Tandem Solar Cells by Revitalizing the Buried Tin‐Lead Perovskite Interface

Abstract Narrow‐bandgap (NBG) mixed tin‐lead (Sn‐Pb) perovskite solar cells (PSCs) serve as crucial top subcells in all‐perovskite tandem solar cells (TSCs). However, the prevalent use of poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) hole transport layers (HTLs) in NBG PSCs compromises device efficiency and stability. To address this, the study proposes a revitalizing strategy for the buried interface of Sn‐Pb perovskites by directly immersing acetylcholine chloride (ACh) into PEDOT: PSS. ACh acts as a proficient “diver,” not only modulating the bottom PEDOT: PSS HTLs but also facilitating the reconstruction of the buried interface and significantly enhancing the quality of the top perovskite layers. This intervention with ACh prevents Sn²⁺ oxidation, mitigates buried defects, and encourages the growth of large, densely packed grains within Sn‐Pb perovskites. Consequently, the optimized NBG PSCs exhibit significantly improved hole transport and reduced carrier recombination, achieving a steady‐state efficiency of 22.98% with enhanced stability. Furthermore, these optimized NBG Sn‐Pb cells enable highly efficient two‐terminal and four‐terminal all‐perovskite TSCs, boasting steady‐state efficiencies of 27.54% (certified at 26.41%) and 28.01%, respectively. This study emphasizes the importance of optimizing NBG PSCs through buried interface reconstruction, propelling the advancement of all‐perovskite TSCs.