Grain boundary regulation of flexible perovskite solar cells via a polymer alloy additive

Due to the rapid processes in perovskite solar cells (PCSs), the flexible PCSs have triggered more and more attention for distributed generation. The fragility of perovskite crystals and quality of perovskite films on flexible substrate are main challenges for the further improvement. Recently, some polymer additive, such as poly(methyl methacrylate) (PMMA) assistance method for crystal growth have been widely reported. However, the fragile PMMA could not provide a desirable mechanical endurance for flexible PSCs. Here, we demonstrate a polymer alloy, which can simultaneously benefit the crystal growth and improve the flexibility. With this approach, a fully covered and compact perovskite film is achieved with a smooth surface. As a result, an enhanced efficiency of 17.54% and 14.01% for rigid and flexible PSCs is demonstrated, respectively. More importantly, the polymer alloy dramatically improves the mechanical stability of the devices, which shows a great potential for future applications in wearable electronics.