Despite significant progress, the efficiency of organic solar cells (OSCs) remains limited by compound losses. In organic semiconductors, photogenerated electrons and holes typically bind as localized excitons. The conversion from excitons to free charges requires a diffusion and dissociation process with parasitic recombination losses. The crystallization behavior of the active layer affects exciton diffusion and dissociation efficiency.

Recently, Li Hongxiang from Sichuan University, Liu Yahui, Liu Yuqiang from Qingdao University, Bo Zhishan from Beijing Normal University and others carefully designed different additives to control the crystallization behavior. The authors found that controlling the aggregation of non-fullerene acceptors can improve the crystallinity of the active layer. In addition, the π-π stacking of the blend becomes more compact while the crystallinity in the vertical direction becomes more uniform. All these benefits exciton diffusion and dissociation.

As a result, the compound losses were reduced and the power conversion efficiency (PCE) was significantly improved. Moreover, the universality of additives in various organic photovoltaic systems has been demonstrated, achieving 19.3% PCE in D18:BTP-eC9-4F OSCs.