Polymer-modified CsPbI2Br films for all-inorganic planar perovskite solar cells with improved performance

All-inorganic CsPbI2Br perovskite with relatively high phase stability and a suitable band gap has been considered as a promising candidate for photovoltaic application. However, in comparison with its organic–inorganic counterparts, it still shows unsatisfactory efficiency and high moisture sensitivity. Here, polyethylene glycol (PEG) is introduced into the CsPbI2Br precursor solution. It is revealed that Lewis base PEG interacts with Pb2+, which can slow down the crystallization rate, regulate the energy levels, and passivate the defect density of CsPbI2Br films. As a result, the optimized devices with PEG exhibit a power conversion efficiency (PCE) of 13.59% under one sun illumination (100 mW cm‒2), which is considerably higher than that of the control devices (10.09%), owing to the reduced nonradiative recombination losses for the former CsPbI2Br films. The results demonstrate that using polymer additives to improve the device performance is an effective strategy for all-inorganic perovskite solar cells.