Efficient and Stable Pure Α-Phase FAPbI3 Perovskite Solar Cells with a Dual Engineering Strategy: Additive and Dimensional Engineering Approaches

Formamidinium lead triiodide (FAPbI3) perovskite solar cells (PSCs) with a certified 25.5% power conversion efficiency (PCE) are the most promising devices for next-generation of solar cells. Here, we focus on boosting the performance and stability of these types of PSCs through a two-step engineering method, first additive engi-neering based on propionic acid for 3D FAPbI(3) PSCs. Second, post-treatment of 3D devices with a 2-(4-fluo-rophenyl)ethyl ammonium iodide (FPEAI) solution doped with nitrosonium tetrafluoroborate (NOBF4). This two-step approach improves carriers' lifetime and charges separation at 3D/2D perovskite/hole transport layer (HTL), tiding with improvements in photovoltaic properties of corresponding PSCs. Besides, NOBF4 p-type dopant increases hole mobility at the interface of the 3D/2D hybrid perovskite/HTL, thus providing a road to-wards more boosting efficiency and stability of PSCs through dimensional engineering. Leading to improved properties of the perovskite, the modified 3D/2D PSCs achieve a PCE of up to 23.18% with long-term shelf, thermal and operational stability.