Modulating the grain size, phase and optoelectronic quality of perovskite films with cesium iodide for high-performance solar cells

The formation of smooth, dense, and uniform perovskite layers on substrates is crucial for achieving high-performance perovskite devices. Here, we show that the introduction of a small concentration of cesium iodide to the precursor solution has a considerable effect on the morphology, phase and optoelectronic properties of CH3NH3PbI3-based perovskite films. An optimized concentration of 3% produces a high-quality perovskite film with a large grain size of similar to 1.8 mu m and a root mean square roughness of 5.917 nm. The improved morphology and high optoelectronic quality of the perovskite layer were verified by SEM, AFM, XRD, and UV-visible, photoluminescence and electrochemical impedance spectroscopy. The defect-free thin perovskite layer enables the fabrication of a mesoscopic CH3NH3PbI3-based perovskite device under ambient conditions, with a maximum power conversion efficiency of similar to 19% with negligible hysteresis and high reproducibility. This method can be extended to other complexes of perovskite used in the present state-of-the-art perovskite solar cells.