Photo-Cross-Linked Fullerene-Based Hole Transport Material for Moisture-Resistant Regular Fullerene Sandwich Perovskite Solar Cells.

Despite the high efficiencies currently achieved with perovskite solar cells (PSCs), the need to develop stable devices, particularly in humid conditions, still remains. This study presents the synthesis of a novel photo-cross-linkable fullerene-based hole transport material named FT. For the first time, the photo-cross-linking process is applied to PSCs, resulting in the preparation of photo-cross-linked FT (PCL FT). Regular PSCs based on C-sandwich architectures were fabricated using FT and PCL FT as dopant-free hole transport layers (HTLs) and compared to the reference spiro-OMeTAD. The photovoltaic results demonstrate that both FT and PCL FT significantly outperform pristine spiro-OMeTAD regarding device performance and stability. The comparison between devices based on FT and PCL FT demonstrates that the photo-cross-linking process enhances device efficiency. This improvement is primarily attributed to enhanced charge extraction, partial oxidation of the HTL, increased hole mobility, and improved layer morphology. PCL FT-based devices exhibit improved stability compared to FT devices, primarily due to the superior moisture resistance achieved through photo-cross-linking.