Redox Shuttle-Stabilized Tin–Lead Perovskites for All-Perovskite Tandem Solar Cells

Tin–lead (Sn–Pb) mixed perovskite solar cells (PSCs) emerge as essential subcells for all-perovskite tandem devices. However, their efficiency and stability are compromised by the facile oxidation of Sn²⁺ to Sn⁴⁺ and substantial defect density. In this work, we introduced tris(2-carboxyethyl) phosphine (TCEP) as a redox shuttle to accelerate the redox-reaction-enabled self-healing of Sn–Pb perovskite to recover its original state under illumination. Meanwhile, TCEP can regulate the crystallization kinetics due to the coordination interaction with metal cations, markedly enhancing the film quality. Benefiting from the multifunctionality of TCEP, the champion single-junction Sn–Pb PSC delivers an improved power conversion efficiency (PCE) of 23.86% while maintaining 90% of its initial PCE after 563 h of maximum power point tracking (MPPT) under illumination. Moreover, the all-perovskite tandem cell with TCEP exhibits a champion PCE of 28.86% and retains 80% of its initial PCE after 1000 h under continuous illumination.