Influence of p-π conjugation in π-π stacking molecules on passivating defects for efficient and stable perovskite solar cells

A comprehensive understanding of the relevance between molecular structure and passivation ability to screen efficient modifiers is essential for enhancing the performance of perovskite solar cells (PSCs). Here, three similar π-π stacking molecules namely benzophenone (BPN), diphenyl sulfone (DPS), and diphenyl sulfoxide (DPSO) are used as back-interface modifiers in carbon-based CsPbBr₃ PSCs. After investigation, the results demonstrate the positive effect of the p-π conjugation characteristic in π-π stacking molecules on maximizing their passivation ability. The p-π conjugation of DPSO enables a higher coordinative activity of oxygen atom in its SO group than that in OSO group of DPS and CO group of BPN, which gives a superior passivation effect of DPSO on defects of perovskite films. The modification of DPSO also significantly improves the p-type behavior of perovskite films and the back-interfacial energetics matching, inducing an increase of hole extraction and a decrease of energy loss. Finally, the unencapsulated carbon-based CsPbBr₃ PSCs with DPSO achieve a maximum power conversion efficiency of 10.60% and outstanding long-term stability in high-temperature, high-humidity (85 °C, 85% relative humidity) air environment. This work provides insights into the influence of the structure of π-π stacking molecules on their ability to improve the perovskite films quality and therefore the PSCs performance.