Overcoming the Limitation of Cs₂AgBiBr₆ Double Perovskite Solar Cells Through Using Mesoporous TiO₂ Electron Extraction Layer

Lead‐free double perovskite Cs₂AgBiBr₆ has gained increasing attention recently. However, the power conversion efficiency (PCE) of Cs₂AgBiBr₆ perovskite solar cells (PSCs) is still low compared with their lead‐based counterparts. Here, by using photoluminescence (PL), time‐resolved photoluminescence (TRPL), and ultrafast transient absorption (TA) measurements, the unbalance between the electron and hole in diffusion and transfer, which limits the performance of the Cs₂AgBiBr₆ PSCs, was further revealed. Considering this issue, a strategy of using the mesoporous TiO₂ electron transport layer (ETL) to construct a bulk heterojunction in Cs₂AgBiBr₆ PSCs was proposed. Consequently, the PCE had improved by over 24% comparing with that only used compact TiO₂ ETL. Moreover, based on mesoporous TiO₂, the unencapsulated Cs₂AgBiBr₆ PSCs maintained 90% of their initial performance after approximately 1200 h of storage in a desiccator (humidity ~30%). This work gives further understanding of Cs₂AgBiBr₆ perovskite and demonstrates that a proper design of balancing the electron and hole diffusion can improve device performance.