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

Abstract

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.