Carrier Dynamics and Morphology Regulated by 1,8-Diiodooctane in Chlorinated Nonfullerene Polymer Solar Cells

Very small amounts of 1,8-diiodooctane (DIO) are very effective at optimizing the performance of polymer solar cells (PSCs). To date, the underlying influences are not yet fully understood, especially in nonfullerene PSCs. Herein, the influence of DIO on carrier dynamics and morphology in the PBDBT2Cl:IT4F system was investigated in detail. We combined the characterization of the transient dynamics with the morphology characterization of PSC devices to explore the origin of enhanced performance. Compared to the cast device, the champion device with 0.5% DIO revealed the maximum of current density (J(sc)) and fill factor (FF). The optimum DIO content helps to enhance carrier transport and optimize morphology, while excess DIO produces adverse effects due to the induced intense aggregation and dilated size in blend films. The results provide some hints of improved device performance upon using DIO as an additive in nonfullerene PSCs.