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 (V_OC) of 1.324 V, which are much higher than those of the control one with a PCE of 8.48% and an V_OC 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.