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

ABSTRACT 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 cm 2 and 28.83% (certified 28.49%) on 1 cm 2 devices.