The Asymmetric Strategy of Small-Molecule Materials for Organic Solar Cells

The conjugated small-molecule materials of organic solar cells have always played a crucial role in light-harvesting, charge transport, morphology optimization, and the attainment of efficient devices. The advancement of novel materials and the understanding of underlying molecular design rules serve as the driving force for furthering efficient and stable photovoltaic devices. Among a variety of design principles, the symmetry-breaking strategy, which is well developed in 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2 ',3 '-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC)-series acceptors, recently demonstrates great potential in small-molecule acceptors and donors for realizing high power conversion efficiency. In this review, in order to give a deep insight on asymmetric strategy, the small-molecule acceptors and donors are systematically summarized with asymmetric structure to elucidate structure-performance relationship, molecular packing behaviors, and morphology evolution. Not only the delicate balance between open circuit voltage and short-circuit current density, but also the reductions in charge recombination and non-radiative recombination are considered to play the key points in improving the photovoltaic performance when the asymmetric molecule is used as host or guest materials. Finally, concise challenges and outlooks are provided for the future development and application of asymmetric molecules and symmetry-breaking strategies. This review systematically summarizes asymmetric small-molecule acceptors and donors, exploring their structure-performance relationship, molecular packing, and morphology. Balancing open circuit voltage and short-circuit current density, reducing charge recombination and non-radiative recombination are crucial for enhancing photovoltaic performance in asymmetric materials. Finally, challenges and prospects for future development and application of asymmetric molecules and asymmetric strategies are discussed. image