Enhanced crystallization and performance of formamidinium lead triiodide perovskite solar cells through PbI₂-SrCl₂ modulation

An innovative strategy using strontium chloride (SrCl₂) as an additive to modulate the crystallization of formamidinium lead triiodide perovskite was developed in a sequential two-step deposition. The results from structural, elemental, and morphological analyses reveal that the SrCl₂ additive is capable of improving the quality and morphology of the pre-deposited PbI₂ layer by forming a PbI₂-SrCl₂ interphase complex through plausible solid-solid interactions. This modulates the subsequent reaction between PbI₂ and formamidinium iodide (FAI) to enhance the crystallinity of the prepared perovskite film with denser and larger grain domains. The concomitantly enhanced optoelectronic properties of the SrCl₂-derived perovskite film enables an improved power conversion efficiency (PCE) of 18.44% with good reproducibility, which surpasses the performance (PCE: 15.94%) of the control device without SrCl₂. This work demonstrates a useful methodology to modulate the morphology and quality of perovskites through solid-solid interactions for achieving high-performance solar cells.