Phenazine-Based Ultra-Narrow Bandgap Acceptors for Efficient Transparent Organic Photovoltaic.

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.