Fluorene-Terminated π-Conjugated Spiro-Type Hole Transport Materials for Perovskite Solar Cells

Spiro-OMeTAD is a widely used hole transport material (HTM) in perovskite solar cells (PSCs), but its inherent low hole mobility and poor thermal stability affect the overall performance of PSCs. To overcome these limitations, we develop a series of fluorene-terminated Spiro-type HTMs, engineered by modulating the fluorene substitution site and pi-conjugated intensity. Among these, the p-BM material exhibits high energetic ordering in film, appropriate energy levels, and efficient carrier extraction, enabling PSCs to achieve power conversion efficiencies (PCEs) of 25.5% and 24.03% for aperture areas of 0.0625 and 1 cm2, respectively. Additionally, a perovskite solar mini-module (size 16 cm2) based on p-BM HTM achieved a PCE of 22.4%. More importantly, p-BM exhibits a high glass transition temperature and enhanced film hydrophobicity, significantly improving the stability of devices in relation to heat and humidity. Our findings provide a promising alternative HTM for developing efficient and stable perovskite photovoltaic devices.