Sterically-extended asymmetric conjugated hole-selective layer for perovskite/silicon tandem solar cells

Carbazole-based self-assembled monolayers (SAMs) were widely adopted as hole-selective layers (HSLs) and recombination junction material in perovskite/silicon tandem solar cells (P/S-TSCs), yet it remains challenging to simultaneously suppress excessive molecular aggregation and maintain continuous charge-transport pathways, particularly on textured silicon substrates. Herein, we report series of sterically extended asymmetric carbazole-based SAMs, 4-(11H-benzo[a]carbazol-11-yl)benzoic acid (BABCz), 4-(9H-dibenzo[a,c]carbazol-9-yl)benzoic acid (BADBCz), and 4-(3',6'-dimethoxy-9H-[3,9'-bicarbazol]-9-yl)benzoic acid (MeO-BADCz), in which MeO-BADCz engineers to construct a continuous three-dimensional C-H···π-mediated charge-transport network while effectively restraining long-range crystallization. The MeO-BADCz monolayer combines strong anchoring to substrate, pronounced work-function modulation, and efficient defect passivation at the buried interface, enabling pinhole-free, highly crystalline wide-bandgap (1.68 eV) perovskite films with suppressed non-radiative recombination. Through these advancements, the optimized wide-bandgap perovskite solar cells (PSCs) incorporating MeO-BADCz as the HSL deliver a power conversion efficiency (PCE) of 24.05% with negligible hysteresis and retain 97.1% of their initial efficiency after 1000 h of continuous operation under ISOS-L-1 protocol. When implemented as the recombination layer on textured silicon heterojunction (SHJ), MeO-BADCz further enables P/S-TSCs with a certified PCE of 33.04% and robust stability under damp-heat-light conditions. This work demonstrates a steric-engineering concept for asymmetric carbazole-based SAMs and highlights texture-tolerant multidimensional charge-transport networks as a key motif for scalable tandem photovoltaics.