Simultaneously Enhanced Efficiency and Operational Stability of Nonfullerene Organic Solar Cells via Solid-Additive-Mediated Aggregation Control

The additive strategy is widely used in optimizing the morphology of organic solar cells (OSCs). The majority of additives are liquid with high boiling points, which will be trapped within device and consequently deteriorate performance during operation. In this work, solid but volatile additives 2-(4-fluorobenzylidene)-1H-indene-1,3(2H)-dione (INB-F) and 2-(4-chlorobenzylidene)-1H-indene-1,3(2H)-dione (INB-Cl) are designed to replace the common 1,8-diiodooctane (DIO) in nonfullerene OSCs. These additives present during solution casting but evaporate after moderate heating. Molecular dynamics simulations show that they can reduce the adsorption energy to improve π-π stacking among nonfullerene acceptor (NFA) molecules, an effect that enhances light absorption and electron mobility. Both INB-F and INB-Cl enhance efficiency, with INB-F achieving a maximum efficiency of 16.7% from 15.1% of the reference PBDB-T-2F (PM6):BTP-BO-4F (Y6-BO) cell, and outperforming DIO. Remarkably, they can simultaneously enhance the operational stability, with the INB-F-treated OSC maintaining over 60% of the initial efficiency after 1000 h operation, demonstrating a T₈₀ lifetime of 523 h, which is a significant improvement over T₈₀ values of 66.2 h for the reference and 6.6 h for DIO-treated OSC. The simultaneously enhanced efficiency and operational lifetime are also effective in PM6:BTP-BO-4Cl (Y7-BO) OSCs, demonstrating a universal strategy to improve the performance of OSCs.