n-type absorber by Cd2+ doping achieves high-performance carbon-based CsPbIBr2 perovskite solar cells

High efficiency and stability have long been the key issues faced by perovskite solar cells (PSCs). It is found that the CsPbIBr2 all-inorganic perovskite has a suitable band gap and satisfactory stability, so it has attracted much attention. However, the many defects in the CsPbIBr2 film are one of the main problems hindering the improvement of power conversion efficiency (PCE) of the CsPbIBr2 PSCs. The substitution of trace impurities is undoubtedly a simple, cost-effective and efficient strategy. In this work, an appropriate amount of Cd2+ (1.0% mol of Pb2+) is added into the CsPbIBr2 precursor solution to fabricate high quality CsPbIBr2 film with improved crystallinity, reduced trap density, suppressed photo-generated carrier recombination, displayed n-type doping and optimized energy level alignment. The corresponding carbon-based all-inorganic Cd2+-doped CsPbIBr2 PSCs achieve a maximum PCE of 10.63% with a high open circuit voltage (VOC) of 1.324 V, which are much higher than those of the control one with a PCE of 8.48% and an VOC of 1.235 V. The unencapsulated device can still retain more than 92% of the initial PCE when stored at ambient atmosphere (25 °C, relative humidity about 30%) for 40 days.