Surface passivation using pyridinium iodide for highly efficient planar perovskite solar cells

Perovskite solar cells have developed rapidly in the past decades. However, there are large amounts of ionic defects at the surface and grain boundaries of perovskite films which are detrimental to both the efficiency and stability of perovskite solar cells. Here, an organic halide salt pyridinium iodide (PyI) is used in cation–anion-mixed perovskite for surface defect passivation. Different from the treatment with Lewis base pyridine (Py) which can only bind to the under-coordinated Pb ions, zwitterion molecule PyI can not only fill negative charged iodine vacancies, but also interact with positive charged defects. Compared with Py treatment, PyI treatment results in smoother surface, less defect densities and non-radiative recombination in perovskite, leading to an improved VOC, negligible J–V hysteresis and stable performance of devices. As a result, the champion PyI-treated planar perovskite solar cell with a high VOC of 1.187 V achieves an efficiency of 21.42%, which is higher than 20.37% of Py-treated device, while the pristine device without any treatment gets an efficiency of 18.83% at the same experiment conditions.