Chlorine-Substituted Double-Cable Conjugated Polymers with NearInfrared Absorption for Low Energy Loss Single-Component Organic Solar Cells

Abstract: Single-component organic solar cells (SCOSCs) have emerged as promising candidates for renewable energy applications due to their simplified film fabrication process and well-controlled morphology. High-performance SCOSCs typically employ active layer materials comprising block copolymers and double-cable conjugated polymers. Among these, double-cable conjugated polymers have attracted a lot of interest in SCOSCs due to their precisely defined structure and easily controllable microphase morphology. In the early stages of double-cable conjugated polymers, most of them contain the polythiophene backbone and fullerene side units, severely limiting the development of SCOSCs. Fortunately, the emergence of novel materials has progressively led to the development of new types of double-cable conjugated polymers. Double-cable conjugated polymers based on acylimide compound have exhibited device performances exceeding 8%. Nevertheless, acylimide-type electron acceptors exhibit a limited photo-response range, resulting in lower photocurrents in SCOSCs. The utilization of A-D-A-type electron acceptors (where D represents electron-donating groups and A represents electron-withdrawing groups) have effectively broadened the absorption spectra of materials due to induced intramolecular charge transfer. Double-cable polymers using A-D-A-type electron acceptors as the side units have achieved efficiencies exceeding 10%. However, significant voltage losses have hampered further improvements in their performance. Chlorine atoms play a crucial role in organic solar cells due to enhanced crystallinity in both chlorine-substituted donor polymers and acceptor molecules, and they can also adjust material energy levels and optimize film morphology. Nevertheless, their role in SCOSCs has been scarcely explored. This limitation arises from the increased complexity of morphology control in double-cable conjugated polymers, where the donor and acceptor segments are covalently linked in one molecule making their crystalline behavior more complicated on account of their mutual restraint. In this study, we have designed and synthesized chlorine-substituted double-cable conjugated polymers, denoted as as-DCPIC-Cl and as-DCPIC-2Cl. The results indicate that the introduction of chlorine atoms into the conjugated backbone reduces energy losses in the devices, resulting in an enhancement of open-circuit voltage (VOC). However, the introduction of chlorine atoms also leads to unbalanced charge transport and increased trap-assisted charge recombination, causing a decrease in the fill factor (FF) and short-circuit current density (JSC). Meanwhile, Grazing-incidence wide-angle X-ray scattering (GIWAXS) tests demonstrate that the introduction of chlorine atoms does not affect the aggregation/crystallization behavior of acceptor units. SCOSCs based on as-DCPIC-Cl achieved a power conversion efficiency (PCE) of 10.14%, which is among the best PCEs reported for SCOSCs based on non-fused electron acceptors.