Modulating Crystallization of Perovskite Thin Films via Zero‐Dimensional Cs 4 PbBr 6 Nanocrystals

Abstract Formamidinium lead iodide perovskite and its derivatives, such as FA 0.90 MA 0.05 Cs 0.05 PbI 3 (band gap ≈1.56 eV), are promising for use in solar cells. However, uncontrolled growth and transformation of perovskite (111) facets during the crystallization process poses a challenge for the production of high‐efficiency and long‐term stability devices. Here, a zero‐dimensional perovskite decoration method is shown to improve the facet regularity of FA 0.90 MA 0.05 Cs 0.053 films by suppressing the formation of (111) facets in the perovskite crystallization process. Due to its unique crystal structure, the zero‐dimensional Cs 4 PbBr 6 /CsPbBr 3 (a composite of phases Cs 4 PbBr 6 and CsPbBr 3 with Cs 4 PbBr 6 as the major phase) nanocrystal acts as a pinning particle, i.e., as a spatial obstacle, to prevent the uncontrolled growth of specific crystal facets during crystallization. The FA 0.90 MA 0.05 Cs 0.05 PbI 3 perovskite decorated with Cs 4 PbBr 6 /CsPbBr 3 improves power conversion efficiency to 25.52% in standard test conditions with high open circuit voltage of 1.177 V. The encapsulated devices maintain more than 93.8% of their original efficiency after exposure to 1500 h of continuous 1‐sun illumination under Maximum Power Point Tracking conditions at 50–55 °C.