Fluorene-Carbazole Based Self-Assembled Hole Transport Monolayers for Efficient Inverted Perovskite Solar Cells

The power conversion efficiency (PCE) and stability of inverted perovskite solar cells (PSCs) have been significantly improved due to the rapid development of self-assembled monolayers (SAMs). SAMs with carbazole derivatives are widely used in inverted PSCs as a promising hole transport material. However, the uneven coverage of SAMs on rough substrates, interface losses caused by agglomeration, and energy level mismatch limit the further improvement of the device's PCE and stability. Here, a new SAM (named 4PACDF) based on the carbazole unit of 4PACz using fluorene for extended conjugation is designed and prepared. Compared to the traditional 4PACz, 4PACDF features extended conjugation and an enhanced asymmetric structure, resulting in a greater dipole moment and improved energy alignment with the perovskite. The existence of methyl groups on 4PACDF suppresses excessive molecular aggregation of 4PACDF, allowing its uniform distribution on fluorine-doped tin oxide. The 4PACDF-based PSCs achieved PCEs of 25.38% (0.09 cm²) and 24.30% (1 cm²), and the device also exhibited excellent stability, retaining 89% of the initial efficiency after 2000 h for the encapsulated device in air (25 °C, 25% RH).