In Situ Condensation of Organosilane Crosslinkers for Ambient‐Processed Inverted Organic Solar Cells with 18.29% Efficiency

ABSTRACT Ambient fabrication processes are essential for the industrial production of high‐efficiency organic solar cells (OSCs). Nevertheless, achieving both high efficiency and long‐term stability under ambient conditions remains a major challenge. Herein, vinyltrimethoxysilane (VTMS) is introduced as an organosilane crosslinker that hydrolyzes and condenses in air to form a “Si─O─Si” crosslinking network, which stabilizes the metastable bulk heterojunction film and enables the fabrication of efficient and stable inverted OSCs under ambient conditions. The strong interfacial interactions between VTMS and the active layer effectively regulate molecular packing, reducing the crystallinity disparity between the donor and acceptor and thus promoting charge transport in the device. As a result, the inverted PM6:BTP‐eC9 device with VTMS incorporation delivers a power conversion efficiency (PCE) of 18.29%, surpassing the pristine device (16.82%), accompanied by an improved fill factor from 73.9% to 77.4%. The optimized devices also exhibit excellent stability, with the unencapsulated VTMS‐added device retaining 92.96% of its initial PCE after 2875 h at 35% relative humidity under ambient conditions, and 90.11% after 1320 h of thermal aging at 85°C in nitrogen. The in situ condensation of organosilanes significantly mitigates moisture‐induced degradation, enabling one of the highest efficiencies reported for inverted OSCs under ambient conditions.