Toward High-Performance Semitransparent Organic Photovoltaics with Narrow-Bandgap Donors and Non-Fullerene Acceptors

Solar energy offers an alternative solution to the global community's growing energy demands. Semitransparent organic photovoltaics (ST-OPVs) have received tremendous attention due to their tunable energy levels and rising power conversion efficiency (PCE). Because of its transparency, ST-OPVs are able to serve as the power-generating roof of the greenhouse, and color-tunable walls/windows for modern buildings or facades. With the rapid development of narrow-bandgap semiconductors to absorb near-infrared photons, the performances of ST-OPVs has progressed with PCEs over 12% with average visible transmittances over 20%. Here, recent developments in ST-OPVs based on narrow-bandgap donors and non-fullerene acceptors are reviewed. Several strategies for chemical structures design have been reported to lower bandgaps semiconductor materials. The recent developments of non-fullerene acceptor structures for ST-OPVs are categorized into A-D-A, A-pi-D-pi-A, and A-DAD-A by the structure alignment. From device perspectives, the strategies such as ternary blend, distributions of donors and acceptors in active layers, tandem and transparent conductive electrodes for high-performance ST-OPVs are summarized. To conclude, some insightful guidelines for future developments in ST-OPVs from both materials and device points of views are provided.