“Standing up” SAMs for Efficient Wide Bandgap and All‐Perovskite Tandem Solar Cells

ABSTRACT All‐perovskite tandem solar cells (all‐PSK TSCs) offer a promising route to surpass single‐junction efficiency limits, yet the performance of wide‐bandgap (WBG) subcells remains constrained by inadequate interfacial engineering. In particular, the molecular orientation and packing of self‐assembled monolayers (SAMs) can significantly influence perovskite film formation and device performance. Here, we rationally design a series of carbazole‐based SAMs and identify a bicarbazole‐core molecule, 9,9‐DCz, that adopts a predominantly upright orientation on indium tin oxide (ITO), in contrast to the conventional flat‐lying alignment. This vertical configuration facilitates denser surface coverage, favorable energy‐level alignment, and reduced non‐radiative recombination in the WBG perovskite layer. As a result, we achieve a certified power conversion efficiency (PCE) of 19.95% (champion 20.81%) for the WBG subcell (1.77 eV, 0.0396 cm ² ), and 28.59% for the all‐PSK tandem device. Our findings indicate that upright SAMs orientation as an effective design principle for high‐performance WBG and tandem perovskite photovoltaics.