Recent advances in polymeric and small molecule donor materials for Y6 based organic solar cells

Organic solar cells (OSCs) have emerged as a promising alternative to traditional inorganic solar cells due to their environmentally friendly nature and inexhaustible solar energy potential. Recent advancements in non-fullerene acceptors (NFAs), particularly the novel NFA Y6 with an acceptor-donor-acceptor (A-D-A) type structure, have significantly boosted the power conversion efficiency (PCE) of OSCs, surpassing 18%. The Y6-based OSCs have demonstrated high open circuit voltage (VOC), short circuit current density (JSC), and fill factor (FF), marking an important milestone in OSC progress. This review focusses exclusively on Y6-based OSCs and their potential to revolutionize the field. It discusses the design strategies and structure-performance relationship for efficient donor materials, with emphasis on polymeric and small molecule donors (SMD). The review highlights the challenges and opportunities in achieving further efficiency improvements beyond 20% for polymeric donors and 16% for small molecules. By leveraging the unique properties of Y6-type acceptors, such as stronger light absorption and tunable energy levels, researchers have achieved remarkable progress in OSC performance. The rational molecular optimization of polymer donors, complementing Y6's narrow bandgap with wide bandgap polymers, and achieving sufficient driving force for charge separation through lower highest-occupied molecular orbital (HOMO) levels, have contributed to the significant PCE enhancements. While Y6-based OSCs have demonstrated great potential, this review also discusses the use of SMD as an increasingly attractive option, offering advantages such as convenient material synthesis and improved crystallinity for higher VOC. Overall, this comprehensive review presents the most advanced developments and insights, paving the way for further advancements in Y6-based OSC technology.