A novel dopant replacing LiTFSI and TBP in Spiro-OMeTAD for high-performance perovskite solar cells

The Spiro-OMeTAD is one of the most widely used hole transport materials in highly efficient perovskite solar cells (PSCs), whose performance typically relies on dopants such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 4-tert-butylpyridine (TBP) to enhance conductivity and hole transport efficiency. However, these conventional dopants suffer from high volatility and hygroscopicity, severely limiting the long-term stability and commercialization potential of PSCs. To solve this problem, this work developed a novel dopant 4-isopropyl-4′-methyldiphenyl iodide tetrakis(pentafluorophenyl)borate (IMT) as a substitute for LiTFSI and TBP for synergistic doping regulation of Spiro-OMeTAD. It was revealed that IMT possessed a well-delocalized electronic structure and appropriately aligned energy levels, which effectively promoted the oxidation of Spiro-OMeTAD, thereby enhancing its electrical conductivity and hole mobility. Additionally, the incorporation of IMT improved the hydrophobicity and compactness of the Spiro-OMeTAD film, effectively mitigating moisture penetration and suppressing interfacial ion migration. The rigid and flexible PSCs based on IMT doping exhibited excellent optoelectronic performance, with the champion power conversion efficiencies reaching 24.97 % and 23.15 %, respectively, which were significantly higher than those of conventional devices using LiTFSI and TBP as dopants. More importantly, the introduction of IMT effectively improved the environmental stability of perovskite devices, enabling them to maintain high-efficiency output under high humidity, high temperature and long-term illumination conditions. This work proposes a new doping strategy for efficient, stable and LiTFSI/TBP-independent PSCs, and provides a theoretical and practical basis for the molecular design of hole transport materials.