In Situ Observation and Control of Crystallization Dynamics for Stable and Efficient CsPbI3-Based 2D Perovskite Solar Cells

Two-dimensional (2D) CsPbI3-based perovskites have shown great potential to tackle the chronic phase instability issue of their three-dimensional (3D) analogue owing to the steric hindrance introduced by the bulky organic spacers. Herein, the high-quality CsPbI3-based 2D perovskite films employing the canonical butylammonium (BA) spacer are fabricated through synergistic thermodynamic and kinetic control of the crystallization process. We show that the film preparation conditions of solvent composition and substrate temperature for spin-coating significantly affect the quality of the resultant films. They are rationalized by scrutinizing the film formation mechanism through in situ grazing-incidence X-ray diffraction investigations. The optimal growth conditions endow the 2D perovskite films with remarkable crystallographic and optoelectronic properties. Solar cells made of this CsPbI3-based 2D perovskite exhibit a power conversion efficiency > 10% with a shelf stability over 160 days, while retaining 80% of the initial performance and an operational stability over 160 min without any loss in performance.