19.0% efficiency binary organic solar cells enabled by using a building block as solid additive

The morphology regulation of active layer has an important role in the development of organic solar cells (OSCs), which can improve device performance and prolong device stability. Herein, we propose the commonly used donors building block, benzo[1,2-b:4,5-b']dithiophene (BDT), as a novel volatile solid additive into PM6:Y-series solar cells. BDT can be well mixed with accepter Y6 by molecular interaction. Therefore, compared with the control film, the BDT-processed film achieves improved aggregation and enhanced crystallinity. Owing to the synergetic effects on the phase separation and molecular arrangement, the device processed with BDT exhibits the significantly enhanced exciton dissociation, charge transfer and collection along with the suppressed bimolecular recombination. Consequently, the device based on PM6:Y6 with BDT-processing obtains the 17.91% power conversion efficiency (PCE) and T90 > 3000 h shelf-life. Meantime, the universality of additive strategy has also been verified in several Y-series accepter OSCs. Impressively, an outstanding PCE of 19.01% is achieved for the BDT-processed PM6:L8BO OSCs, which is one of the highest reported values of PM6:L8BO system. Eventually, this work provides a facile and efficacious approach to manipulate the active layer morphology, improve the photovoltaic performance and stability of OSCs.