Interfacial passivation towards attainment of efficient and stable carbon-based CsPbIBr2 perovskite solar cells at ambient air

Inorganic perovskite solar cells (IPSCs) based on CsPbIBr2 absorber are the recent research interest of solar cell researchers because of their exceptional thermal stability and opto-electronic features. In addition, the perovskite films can be easily optimized by simple solution processing techniques even in open air. However, they encounter several defects on the surface that deteriorate interfacial quality and hamper device performance as well as stability. These defects are usually minimized by surface passivation. Herein, carbon-based IPSCs (C–IPSCs) have been fabricated without a hole-transport layer (HTL) under ambient condition (70 % RH; RT) with different concentration of a novel green deep eutectic solvent (DES) as a passivation layer on CsPbIBr2 (prepared at low temperature) to reduce the defects. Their structural, morphological, optical, electrical, and photovoltaic properties have been analyzed and compared with that of pristine C–IPSCs. The optimal concentration of DES resulted in defect-controlled morphology with enhanced crystallinity and energy level matching. The uncoordinated Pb2+(Cs+) and halide vacancies on the surface of CsPbIBr2 (processed in humid air) are well treated because of the ionic nature of DES. This may also reduce the energy loss at perovskite-carbon interface and thereby the cause of subsequent enhanced charge transfer and efficiency of champion device from 4.73 % to 7.04 % with high photovoltage, fill-factor, current-density, and reduced hysteresis. Also, demonstrated with significantly improved resistance to heat and humidity. Hence, this work may give better understanding to attain higher photovoltaic performance and stability of C–IPSCs in a realistic ambient environment for commercialization through simple solution processing.