Bisphosphonate‐Anchored Self‐Assembled Molecule with Halogen Functionalization for Wide‐Bandgap Perovskite Solar Cells and Tandems

ABSTRACT Wide‐bandgap (WBG) top subcells used in all‐perovskite tandems commonly suffer from substantial open‐circuit voltage ( V OC ) deficits, primarily caused by interfacial defects and non‐ideal energy alignment. Here, we develop bisphosphonate‐anchored indolocarbazole derivatives, bis‐4PACz and bis‐4PACz‐Br, as self‐assembled monolayer (SAMs) hole‐selective contacts. The dual‐anchored SAM molecule design enables enhanced adsorption energy, leading to more uniform coverage on the ITO surface and improved interfacial compatibility with the perovskite layer. Moreover, bromine functionalization in bis‐4PACz‐Br further increases the work function of the substrate and optimizes the energy level alignment with the 1.77 eV WBG perovskite. These favorable characteristics of bis‐4PACz‐Br facilitate efficient hole extraction, suppress interfacial non‐radiative recombination, and enhance interfacial robustness. As a result, the single‐junction WBG cells achieve a power conversion efficiency (PCE) of 21.07% with a high V OC of 1.362 V. When integrated into all‐perovskite tandems, this strategy delivers champion PCEs of 29.89% (certified 29.50%) on 0.05 cm 2 and 28.52% on 1 cm 2 devices. This work introduces a molecular interface strategy aimed at mitigating voltage loss and stability challenges, which are critical for advancing high‐performance all‐perovskite tandem photovoltaics.