Perovskite-type stabilizers for efficient and stable formamidinium-based lead iodide perovskite solar cells

Abstract

Preparation of phase-pure and stable formamidinium-based lead iodide (FAPbI₃) perovskites is essential for fabricating high-performance perovskite solar cells (PSCs). Here, we report using very little CsPbBr₃ perovskite (2%, molar ratio to FAPbI₃) to stabilize the black-phase α-FAPbI₃. Specifically, the as-synthesized CsPbBr₃ powder is added to the PbI₂ precursor. It is found that the interlayer spacing of layered PbI₂ can be stretched due to the formation of the PbI₂–DMSO–CsPbBr₃ intermediate phase, which can promote the penetration of FAI and the transformation to black phase α-FAPbI₃. The incorporation of CsPbBr₃ not only stabilizes the FAPbI₃ phase but also results in a high-quality film with increased grain size and suppressed bulk defects. Therefore, the resultant PSCs exhibit enhanced built-in potential, improved carrier extraction, and suppressed non-radiative recombination. As a result, the corresponding PSCs deliver a champion efficiency of 23.34%. Moreover, the PSCs stabilized with CsPbBr₃ show much improved operational stability, retaining 80% of their initial efficiency after 1153 hours following the maximum power point (MPP) tracking under one sun illumination; while the efficiencies of control devices w/o CsPbBr₃ drop to 80% of their initial efficiencies after 75 hours.