Crystalline grain engineered CsPbIBr2 films for indoor photovoltaics

Indoor photovoltaic devices have garnered profound research attention in recent years due to their prospects of powering 'smart' electronics for the Internet of Things (IoT). Here it is shown that all-inorganic Cs-based halide perovskites are promising for indoor light harvesting due to their wide bandgap matched to the indoor light spectra. Highly crystalline and compact CsPbIBr2 perovskite based photovoltaic devices have demonstrated a power conversion efficiency (PCE) of 14.1% under indoor illumination of 1000 lx and 5.9% under 1 Sun. This study revealed that a reduction in grain misorientation, as well as suppression of defects in the form of metallic Pb in the perovskite film are crucial for maximising the photovoltaic properties of CsPbIBr2 based devices. It was demonstrated that a pinhole free CsPbIBr2/Spiro-OMeTAD interface preserves the perovskite alpha phase and enhances the air stability of the CsPbIBr2 devices. These devices, despite being unencapsulated, retained > 55% of the maximum PCE even when stored under 30% relative humidity for a shelf-life duration of 40 days and is one of the best stability data reported so far for CsPbIBr2 devices.