"Standing up" SAMs for Efficient Wide Bandgap and All-Perovskite Tandem Solar Cells.

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 cm2), 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.