Enhancing Photo‐Stability of All‐Perovskite Tandem Solar Cells via In Situ Construction PEDOT Hole Transport Channels

In all‐perovskite tandem solar cells (TSCs), thick (>1 µm) Sn‐Pb rear sub‐cells suffer from hole accumulation‐driven Sn 2+ photo‐oxidation due to unbalanced charge transport. Traditional sacrificial reductive additives fail to address this photo‐stability challenge. Herein, we employ a low‐temperature solution‐processed solid‐state polymerization (SSP) method using 2,5‐dibromo‐3,4‐ethylenedioxythiophene (DBEDOT) to in situ construct poly(3,4‐ethylenedioxythiophene) (PEDOT) hole transport channels within the perovskite film. This approach enhances hole extraction, therefore balancing electron‐hole transport in Sn‐Pb rear sub‐cells as well as recombination between two sub‐cells. Consequently, we achieve a 24.20% power conversion efficiency (PCE) for single‐junction Sn‐Pb devices and a 29.58% PCE for all‐perovskite TSCs. Significantly, by suppressing Sn 2+ photo‐oxidation through mitigated hole accumulation, the tandem device retains 90% of its initial efficiency after 1100 h of continuous operation at 55°C under maximum power point (MPP) conditions. This strategy offers a promising route toward the development of highly efficient and stable all‐perovskite tandem photovoltaics.