A research team led by Prof. GE Ziyi from the Ningbo Institute of Materials Technology and Engineering from the Chinese Academy of Sciences has developed a low-crystallinity guest acceptor, D-IDT, using a tin-free direct C–H activation method, which was incorporated as a third component into binary organic solar cells (OSCs). This finding resulted in a stable OSC with a power conversion efficiency (PCE) of 19.92%. This study was published in Energy & Environmental Science. 

OSCs have garnered considerable attention in the field of organic electronic devices due to their lightweight, mechanical flexibility, and translucency. However, the synthesis of organic photovoltaic materials for OSCs has traditionally relied on the Stille coupling reaction, which is plagued by complex procedures, high costs, and environmental concerns. As a result, there is a pressing need for more cost-effective and environmentally friendly synthesis methods.

To address this challenge, the research team designed and synthesized an A-D-D-A type guest acceptor, D-IDT, using a direct C-H activation approach. By employing a C-H/C-H cross-coupling strategy, the researchers simplified the synthesis process, achieving a high yield of 84%. When integrated into the D18:BTP-eC9 host system, D-IDT demonstrated superior π-conjugation but significantly weaker intermolecular interactions compared to the A-D-A type guest acceptor S-IDT.

The low crystallinity of D-IDT enhances its miscibility with the host acceptor BTP-eC9, promoting faster aggregation of BTP-eC9 and facilitating efficient exciton dissociation and charge transport. This resulted in a notable reduction in voltage loss, with the ternary device exhibiting an 18 mV lower loss compared to the binary system.

The ternary device incorporating D-IDT achieved a PCE of 19.92%, surpassing the 17.66% efficiency of devices based on S-IDT. This marks the highest efficiency reported to date for OSCs using the D18:BTP-eC9 host system. Furthermore, the D-IDT-treated OSCs demonstrated long-term stability, retaining 92% of their initial efficiency after 200 hours of continuous illumination.

This study highlights the potential of low-crystallinity guest acceptors in controlling crystallization kinetics and fine-tuning the assembly behavior of host acceptors. It provides new insights into the design of efficient third components through green and straightforward synthesis methods, bringing OSC technology closer to commercial viability.

Fig. The D-IDT-treated ternary OSCs with a record high PCE (Image by NIMTE)