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.