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 FT₁₂. For the first time, the photo-cross-linking process is applied to PSCs, resulting in the preparation of photo-cross-linked FT₁₂ (PCL FT₁₂). Regular PSCs based on C₆₀-sandwich architectures were fabricated using FT₁₂ and PCL FT₁₂ as dopant-free hole transport layers (HTLs) and compared to the reference spiro-OMeTAD. The photovoltaic results demonstrate that both FT₁₂ and PCL FT₁₂ significantly outperform pristine spiro-OMeTAD regarding device performance and stability. The comparison between devices based on FT₁₂ and PCL FT₁₂ 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 FT₁₂-based devices exhibit improved stability compared to FT₁₂ devices, primarily due to the superior moisture resistance achieved through photo-cross-linking.