Differential Space‐Limited Crystallization of Mixed‐Cation Lead Iodide Single‐Crystal Micro‐Plates Enhances the Performance of Perovskite Solar Cells

Abstract

The synthesis of certain asymmetric perovskite single crystals (SCs)—including CH3NH3PbI3, which is used most commonly—for application in high‐performance perovskite solar cells (PeSCs), remains very challenging. Herein, a promising but general method, differential space‐limited crystallization (DSLC), is described for synthesizing high‐quality perovskite single‐crystal micro‐plates. The thickness of the perovskite SCs is controlled by the difference between the thicknesses of two sets of polytetrafluoroethylene (PTFE) spacers. Because the DSLC method does not require very thin spacers, it simplifies the procedure of crystal growth. More importantly, the hydrophobicity of the PTFE spacers weakens the attraction between the surfaces of the confined space and the precursor complexes, thereby increasing the rate of diffusion of the precursor ions. Accordingly, the critical nucleation step is not limited by the low rate of diffusion of the ions. This approach is used to prepare mixed‐cation lead iodide single‐crystalline micro‐plates for solar cell applications. The device performance of single‐crystal PeSCs improves after introducing formamidinium ions. The stability of the single‐crystal devices also improves relative to that of conventional thin‐film counterparts. It is anticipated that this DSLC method can also be used to synthesize different types of asymmetrical perovskite SCs for other optoelectronic applications.