Asymmetric Self‐Assembled Molecule With High Dipole Moment for Efficient Wide‐Bandgap Perovskite Solar Cells and Tandems

Self-assembled monolayers (SAMs) have shown considerable promise as hole-transport layers (HTLs) in wide-bandgap (WBG) perovskite solar cells (PSCs) and tandems. However, conventional SAM materials often face limitations such as substantial energy-level misalignment and inefficient charge transport, which limit device performance. Here, we designed a carbazole-based SAM molecule, 4-(8-bromo-11H-benzo[a]carbazol-11-yl) butyl) phosphonic acid (Br-4PhCz), through a combined strategy of asymmetric π-extension and terminal bromine substitution. The resulting Br-4PhCz exhibits a large dipole moment, adopts a face-on molecular orientation with uniform substrate coverage, and demonstrates superior self-assembly quality. As a SAM-based HTL, it enables the deposition of high-quality WBG perovskite films over large areas, reinforces a robust buried interface, minimizes energy-level misalignment, suppresses interfacial non-radiative recombination, and enhances hole extraction. By integrating Br-4PhCz, we obtained an impressive open-circuit voltage of 1.36 V in WBG PSCs with a bandgap of 1.77 eV. Using these high-performance WBG subcells, we fabricated all-perovskite tandem devices that deliver maximum power conversion efficiencies of 29.35% (certified 28.98%) on 0.05 cm² and 28.83% (certified 28.49%) on 1 cm² devices.