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 Sn²⁺ 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 Sn²⁺ 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.