Enhanced charge extraction in carbon-based all-inorganic CsPbBr3 perovskite solar cells by dual-function interface engineering

Highlights: • Dual-function interface engineering are developed to promote charge extraction. • High-quality CsPbBr₃ film and the reduced energy loss are realized simultaneously. • CsPbBr₃ PSC tailored with CsPbI₃ NCs achieves a champion PCE of 9.45%. • All-inorganic CsPbBr₃ PSC free of encapsulation exhibits excellent stability. -- Abstract: Carbon-based all-inorganic CsPbBr₃ perovskite solar cells (PSCs) have attracted growing interests due to low cost and excellent tolerances toward moisture, temperature, oxygen and ultraviolet light. However, carrier recombination of CsPbBr₃ film and large energy level differences at CsPbBr₃/carbon interface are still the most crucial problem for further enhancement of power conversion efficiency. In the current study, an intermediate energy level at CsPbBr₃/carbon interface and CsPbBr₃ film passivation are employed by coating hexane solution of CsPbBr_xI_3-x nanocrystals (NCs) on the perovskite layer. Through systematic study on interfacial engineering, it is found that CsPbBr_xI_3-x NCs with tunable energy level can remarkably reduce energy loss and hexane under passivation treatment can enlarge perovskite grain size as well as reduce trap state density. A champion power conversion efficiency of 9.45% is achieved for CsPbI₃ NCs tailored all-inorganic CsPbBr₃ PSC in comparison with 5.26% for NCs-free device, with the unencapsulated carbon-based CsPbBr₃ PSC exhibiting remarkable long-term stability over 900 h in 80% relative humidity air atmosphere at 25 °C. This work provides an effective approach to promote charge extraction and reduce defect states density as well as enhance the performance of PSCs.