Solution-processed formamidinium lead iodide (FAPbI₃) perovskite is entropically metastable, and it exhibits condition-induced crystal polymorphism. Under an ambient atmosphere, the photoactive black α-FAPbI₃ converts easily to photoinactive yellow δ-FAPbI₃. This αàδ phase degradation is further accelerated upon exposure to high temperature/humidity, directly threatening the performance and stability of perovskite solar cells (PSCs). Herein, CsI-PbI₂:DMSO complex is introduced as a phase stabilizer to modulate the crystallization of α-FAPbI₃ perovskite from δ-FAPbI₃ precursor and simultaneously, serve as a defect passivator to suppress trap states formation. Theoretical simulations and experimental results reveal the pivotal role of complex additive in optimizing the energy band alignment and optoelectronic properties of α-FAPbI₃ perovskite and most importantly, hindering the αàδ phase transition. The best PSC device based on the additive-engineered perovskite film achieved an efficiency of ~21.9%, which is ~11 % higher than that of its pristine counterpart (~19.8%). Additionally, the incorporation of CsI-PbI₂:DMSO complex remarkably enhances the long-term stability and photostability of the PSCs by inhibiting ion migrations and preserving the α-phase in FAPbI₃ perovskite. The additive engineering presented herein offers a route to produce FAPbI₃-based PSCs with improved performance, stability and reproducibility.

January 17, 2023

https://doi.org/10.1002/admi.202201658