Resonator‐Engineered Micro‐Cavity–Driven Coupling for Electromagnetic Field Redistribution in PM6:Y6 Non‐Fullerene Organic Solar Cells

ABSTRACT Efficient photon harvesting in ultra‐thin organic solar cells remains challenging due to limited optical absorption and incomplete light confinement within the active layer. In this work, a resonator‐engineered microcavity architecture is introduced to enhance light–matter interaction in non‐fullerene organic solar cells based on a PM6:Y6 bulk‐heterojunction absorber. The proposed design integrates an asymmetric dielectric–metal–dielectric (ZnO/Ag/WO 3 ) transparent electrode that simultaneously acts as a semi‐reflective mirror, forming a Fabry–Pérot‐type optical resonator with the metallic back contact. Optical and photovoltaic characteristics of the cavity‐free and microcavity‐integrated devices were systematically investigated using the transfer matrix method (TMM) for optical simulations and SCAPS‐based electrical modeling. The microcavity structure reshapes the internal electromagnetic field distribution, enabling resonance‐assisted optical confinement and the formation of standing waves within the active layer. This resonance‐driven field localization strengthens photon–matter interactions and enhances photogeneration without increasing the absorber's geometric thickness. The results demonstrate that microcavity integration provides an effective photonic strategy to improve photon harvesting and device performance in ultra‐thin organic solar cells. Such resonant photonic engineering offers a promising pathway toward high‐efficiency, thin‐film, and potentially semi‐transparent organic photovoltaic technologies.