Mitigating efficiency loss in thick-film organic solar cells by suppressing charge recombination and energetic disorder

Abstract

In the photovoltaic field, organic solar cells (OSCs) are regarded as a promising future alternative owing 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 studies 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 is limited. In this study, we explore the effect of halogen-free dibenzyl ether (DBE) as an additive for bulk heterojunction (BHJ) OSCs to mitigate energetic disorder and reduce charge recombination. By incorporating 0.3 vol% DBE into PTzBI-dF:L8-BO, we achieved a PCE of approximately 16% in a 300-nm-thick active layer, with only a modest reduction in the fill factor (FF) from 77.75% to 70.73%. However, the reference device without DBE showed a significant drop in FF to 55%. Temperature-dependent mobility measurements revealed reduced thermal activation energy (E_a) and narrow density of states (DOS) distribution in the DBE-modified device, correlating with improved charge transport. Optimized thick-film OSCs demonstrated enhanced short-circuit current (J_SC) and external quantum efficiency (EQE) while suppressing recombination. These results indicate 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 thus offers valuable insights into optimizing thick-film OSCs for scalable, high-efficiency, and commercially viable applications.