All‐in‐One Molecule Regulated Buried Interface and Crystallization of Tin–Lead Perovskite for Efficient All‐Perovskite Tandem Solar Cells

Mixed tin–lead (Sn–Pb) perovskite solar cells (PSCs) are critical for advancing all–perovskite tandem solar technologies, as they resolve the efficiency limitations of single‐junction devices. However, the widely used hole transport layer (HTL) poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) restricts performance and durability due to its acidic nature and moisture absorption. Additionally, the rapid crystallization of Sn‐containing perovskites hinders the fabrication of uniform, high‐quality mixed SnPb perovskite films. To address these challenges, this study incorporates 4‐sulfophthalic acid triammonium salt (SATS) as a multifunctional additive into both the PEDOT:PSS layer and perovskite precursor solution. SATS modifies the physicochemical properties of PEDOT:PSS and slows perovskite crystallization, promoting films with enhanced crystallinity. Through these synergistic effects, the optimized single‐junction SnPb PSCs achieve a power conversion efficiency (PCE) of 23.85%. Integrating these devices into two‐terminal all‐perovskite tandem architectures further delivers a remarkable efficiency of 28.74%.