Dual additive strategy to regulate the phase separation of bulk heterojunction layer for efficiency enhancement in non-fullerene organic solar cells

The phase separation of bulk heterojunction (BHJ) layer is critical for the exciton dissociation, charge transport and recombination in non-fullerene organic solar cells (OSCs), therefore accurately regulating the BHJ phase separation must be one of the significant strategies to enhance the performance of non-fullerene OSCs. In this paper, dual additive strategy (1,8-diiodooctane (DIO) and methanol (MeOH)) is proposed to regulate the phase separation of PBDB-TF:IT-4F layer. Experimental studies reveal that this dual additive strategy could decrease domain size which is beneficial to exciton dissociation. Moreover, the extraction of low boiling point MeOH from the BHJ film can bring some IT-4F dissolved in DIO:MeOH:CB toward to the BHJ surface and thus improve the vertical distribution and form an efficient bi-continuous charge transport routes in BHJ layer for balancing charge transport in OSCs. Consequently, with dual additive DIO and MeOH, the short circuit current density raises from 19.79 to 21.13 mA cm⁻², fill factor enhances from 67.73% to 70.86%, and the power conversion efficiency increases from 11.26% to 12.72% with ∼13% improvement. Notably, this dual additive strategy is free of complicated treatment which is suitable for practical application.