Phenyltrimethylammonium-Alloying Strategy for Efficient and Durable Formamidinium-Based Perovskite Solar Cells

As for the commonly used formamidinium lead iodide (FAPbI3) perovskite, adding small amount of larger organic cations is a viable strategy to overcome its instability caused by formamidinium (FA) or iodide (I). Herein, FAPbI3 perovskite is modified by addition of quaternary cation phenyltrimethylammonium (PTMA), which forms 2D perovskite phase. With the presence of PTMA cations and small-sized Br anions, the local strain of perovskite layer is mitigated. Also, X-ray analyses reveal that PTMA cation directs FAPbI3 to have more vertically oriented structure, which aids the enhanced photocarrier generation and extraction. Defect analyses suggest that PTMA bromide alloying also greatly reduces the trap sites. Due to these combined effects, the PTMABr-modified device results in the improved open-circuit voltage plus stability under 60 degrees C or 1 sun illumination, maintaining 80% of its initial efficiency after 1800 and 1400 h, respectively. Addition of phenyltrimethylammonium (PTMA) cations and smaller Br anions causes strain relaxation and changes in crystal orientation, causing the perovskite to have efficient charge transfer and less defective interfaces. The resultant solar cells demonstrate improved efficiency and thermal/light stabilities, with PTMA-bromide-alloyed devices surviving at both 60 degrees C and 1 sun for 1400 h or more.image (c) 2023 WILEY-VCH GmbH