A Multilayered Electron Extracting System for Efficient Perovskite Solar Cells

Power conversion efficiencies of perovskite solar cells (PSCs) have rapidly increased from 3.8% to a certified 25.2% within only a decade. Eliminating possible recombination losses at the interfaces is essential to further improve both efficiency and stability of this class of emerging photovoltaic technology. Herein, a simple approach for improving the electron extraction of the PC₆₀BM electron transport layer (ETL) is presented by sequentially depositing Al:ZnO (AZO) and triphenyl-phosphine oxide (TPPO) on top of it, in a p–i–n device configuration. The efficiency of the resulting CH₃NH₃PbI₃-based solar cell is shown to improve from 14.6%, measured for the control PC₆₀BM-only cell, to 17.9% for double-ETL (PC₆₀BM/AZO) and 19.2% for triple-ETL (PC₆₀BM/AZO/TPPO)-based devices, respectively. Optimized triple-ETL-based cells exhibit high fill factor of 82%. The combination of electrical and quantum mechanical calculations shows that efficiency improvement is attributed to reduced trap-assisted recombination at the interface and better energy level alignment due to chemical interactions between PC₆₀BM, AZO, and TPPO. Moreover, it is shown that the use of multilayer ETL results in better device stability (T₈₀ ≈ 800 h) under constant illumination. This work opens new possibilities for inexpensive highly efficient and stable multilayered contacts for PSCs by combining organic small molecules and metal oxides.