Unveiling the Critical Role of Oxidants and Additives in Doped Spiro-OMeTAD toward Stable and Efficient Perovskite Solar Cells

Chemical dopants are often required in organic hole transport materials (HTMs) to enhance the film conductivity and power conversion efficiency (PCE) of solar cells. Although additives (LiTFSI + tBP) and oxidants (FK209) are key dopants in HTMs, their hygroscopic and volatile nature induce severe morphology change, ion accumulation, as well as perovskite corrosion, which significantly hinder PSC stability. Various dopant structures and compositions have been developed, but challenges remain in fundamentally understanding their complementary effects and individual roles of additives and oxidants in PSCs. In this study, dopants with different configurations were investigated thoroughly toward optimizing the device efficiency and stability. The results show that the additives LiTFSI + tBP play more essential roles in enhancing the spiro-OMeTAD (Spiro) conductivity and device efficiency, even though the oxidant FK209 produces more Spiro+ cations. Consequently, the cooperative effects of additives and oxidants enable the highest conductivity (2 × 10–5 S cm–1) and a PCE of over 21% compared to their individual counterparts. The additives LiTFSI + tBP exhibit deleterious influences on film stability under different environmental conditions, whereas FK209-only devices significantly alleviate these negative effects on device stability, meanwhile achieving a satisfied conductivity (5 × 10–6 S cm–1) and a high PCE of 19.6%. Besides, unencapsulated FK209 devices exhibit remarkable environmental and operational stability. Our work provides new insights into understanding dopants' roles in charge conduction and offers new doping approaches for organic semiconductors.