Toward high-performance organic photovoltaics: the new cooperation of sequential solution-processing and promising non-fullerene acceptors.

Organic photovoltaics (OPVs) have long been a hot topic due to their light weight, low cost, and flexibility. Simple blend-based OPVs have sufficient donor/acceptor (D/A) interfaces and high exciton dissociation efficiency, which result in certified high power conversion efficiency (PCE) exceeding 18%. However, the difficult morphology control and poor device stability limit further progress toward higher PCE and future application. Sequential solution-processing with tunable vertical phase distribution, D/A interfaces, and charge transportation pathways not only benefit device stability but can also overcome the up-scaling challenge. In recent years, the development of non-fullerene acceptors (NFAs) has been very rapid, which is attributed to their tunable energy levels, bandgaps, planarity, and crystallinity. In this minireview, the opportunities for the cooperation of sequential solution-processing and NFAs are revealed based on their characteristics, such as diverse molecular shapes, abundant functional groups and heteroatoms, and various aggregation states for NFAs; independent active layer processing, controllable D/A interfaces, and excellent device stability for sequential solution-processing. Few but important existing examples are discussed to display the prospects of sequential solution-processed fullerene-free OPVs toward high PCE, good device stability, high semitransparency, and large-area industrial manufacture. Finally, some possible research directions are predicted and the main issues that need to be overcome are proposed for sequential solution-processed fullerene-free OPVs toward higher performance.