Phenazine‐Based Ultra‐Narrow Bandgap Acceptors for Efficient Transparent Organic Photovoltaic

Abstract Developing ultra‐narrow bandgap electron acceptors is an effective approach to achieving transparent organic photovoltaics (TOPVs). In this study, two phenazine based non‐fullerene acceptors, namely PA‐2H and PA‐2Br, are synthesized by merging core bromination and extended conjugation. Applying extra ethylene double bonds as π bridge makes the absorption onsets of films red shift to 1021 and 1041 nm for PA‐2H and PA‐2Br, respectively. Single‐crystal data illustrated that PA‐2Br exhibits a tight and ordered 3D network packing with improved charge transport, different from the 2D step‐like packing of PA‐2H. Therefore, PA‐2Br‐based opaque organic photovoltaics achieves an excellent power conversion efficiency (PCE) of 13.7%. Notably, the TOPV attains a PCE of 4.60% with an average visible transmittance (AVT) of 70.2%, which exhibits promise in efficient TOPVs. This work demonstrates the importance of core bromination in the design of high‐performance ultra‐narrow bandgap electron acceptors and provides the opportunity to fabricate efficient TOPVs.