Mitigating Efficiency Loss in Thick-Film Organic Solar Cells via Suppressing Charge Recombination and Energetic Disorder

Abstract

In the photovoltaic field, organic solar cells (OSCs) are regarded as a promising future alternative due to their merits of flexibility, tunable chemical structures, and versatile processing options. However, achieving high power conversion efficiency (PCE) in thick-film OSCs remains a challenge due to issues related to charge recombination, poor charge mobility, and energy disorder. Recent advances have demonstrated that non-fullerene acceptors (NFAs) and device engineering can improve efficiency, but a comprehensive understanding of the PCE losses in thick-film OSCs remains scarce. In this study, we explore the effect of halogen-free dibenzyl ether (DBE) as an additive in bulk heterojunction (BHJ) OSCs to mitigate energetic disorder and reduce charge recombination. By incorporating 0.3 vol% DBE into a PTzBI-dF:L8-BO, we achieved a PCE towards 16% in a 300 nm thick active layer, with only a modest reduction in fill factor (FF) from 77.75% to 70.73%. In contrast, the reference device without DBE showed a significant drop in FF to 55%. Temperature-dependent mobility measurements revealed reduced thermal activation energy (Ea) and narrow density of states (DOS) distribution in the DBE-modified device, correlating with improved charge transport. The optimized thick-film OSCs demonstrated enhanced short-circuit current (JSC) and external quantum efficiency (EQE), while suppressing recombination. These results suggest that DBE additives provide an effective approach to enhance the performance of thick-film OSCs by improving morphological order and charge transport properties. This study offers valuable insights into optimizing thick-film OSCs for scalable, high-efficiency, and commercially viable applications.