Simplifying Organic Photovoltaics Fabrication by Vertical Phase Separation of Electron Transport Layer

Interlayers are a pivotal component in high‐performance organic photovoltaics (OPVs), but their incorporation comes with increased fabrication complexity and manufacturing costs. Herein, codeposition of both the active layer and electron transport layer (ETL) is achieved by a single film‐casting step of a solution containing the polymer donor, small molecule acceptor, and a perylene diimide‐derivative as an additive. By tuning the solubility and surface energy, phase separation of the additive leads to a self‐formed organic ETL with favorable charge extraction and collection efficiencies. This additive engineering is utilized to simplify the fabrication of various bulk‐heterojunction systems based on Y‐series acceptors, realizing metal oxide‐free inverted OPVs. Specifically, cells with PM6:BTP‐eC9 and our self‐formed ETL exhibit power conversion efficiencies of 14%.