Releasing Acceptor from Donor Matrix to Accelerate Crystallization Kinetics with a Second Donor toward High-Efficiency Green-Printable Organic Photovoltaics

The state-of-the-art power conversion efficiency (PCE) of organic solar cells (OSCs) is typically achieved in the devices fabricated by toxic halogen solvents with complex post-treatment processes in strictly inert atmosphere. Developing suitable processing method for printing in ambient air using eco-friendly solvents with continuous solution supply and fabricating efficient devices without any post-treatment are intensively desired. Controlling the crystallization kinetics to fine-tune the acceptor's assembly behavior with a second donor for favorable morphological evolution is an effective approach to achieve above requirements. Herein, a kinetics-controlling strategy is implemented by introducing a strong crystalline small molecule, BTR-Cl, to enhance the crystallinity of acceptors. The combined in situ spectra characterizations revealed that the earlier aggregation of acceptor and modulation in conformation of PM6 can be achieved. This unique aggregation behavior facilitated enhanced film crystallization with reduced paracrystallinity of pi-pi stacking, resulting in improved charge transport and inhibited charge recombination. An outstanding PCE of 17.50% is obtained for the device processed with o-xylene via ambient air printing without any post-treatment. More significantly, efficient all-printed inverted devices and large-area modules are prepared. The generalization of this strategy has been confirmed in other efficient systems, suggesting a great potential for universally fabricating high-efficiency and eco-friendly OSCs.