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.