Manipulating Blend Morphology and Non-Radiative Energy Loss in Organic Solar Cells through 1,8-Dihalooctane Additive Engineering

Despite the widespread implementation of additive engineering in organic solar cells, the intrinsic mechanisms dictating the halogen-dependent efficacy of these additives remain elusive. Herein, we present a systematic investigation into three 1,8-dihalooctane additives (DClO, DBrO, and DIO) within the PM6:L8-BO system, explicitly correlating their modulation behaviors with halogen identity. Our findings demonstrate that the modulation efficacy is intrinsically governed by the halogen substituent: while DIO exhibits the most potent aggregation regulation, it unfortunately induces severe non-radiative energy loss, thereby compromising the open-circuit voltage. Conversely, DClO displays the weakest modulation capability, resulting in restricted current density and fill factor. Notably, DBrO achieves an optimal trade-off between aggregation control and the suppression of non-radiative energy losses. Consequently, devices processed with 0.5 vol % DBrO deliver the best power conversion efficiency of 19.2% alongside a remarkable fill factor of 79.8%, where the DClO- and DIO-treated devices achieved performances of 18.4 and 18.5%, which are higher than the control device (17.2%) without additive. This work offers fundamental insights into halogen-dependent additive behavior, establishing a rational guideline for additive selection to balance morphological control and non-radiative losses in high-efficiency organic solar cells.