Organic photovoltaics (OPVs) are solar cells that can have useful properties such as low weight and flexibility. However, polymer donors for high-performance OPVs, such as PM6, can be costly and difficult to produce at scale, which hampers their commercial application. Poly(3-hexyl-thiophene) (P3HT) is cheaper and easier to produce on a large scale. Thus, developing efficient P3HT:nonfullerene solar cells is an interesting research target. However, the typical efficiency of P3HT:nonfullerene solar cells often lags behind those of PM6-based devices.

The efficiency of OPVs can often be improved by a ternary blending strategy, i.e., blending the host polymer donor:small molecule acceptor mixture with a second small molecule acceptor. However, this strategy used in PM6 systems tends to fail for the development of high-performance P3HT-based ternary OPVs. The efficiencies of ternary blends based on the benchmark host P3HT:ZY-4Cl and a second acceptor have not exceeded 8 %. A new third component suitable for P3HT-based organic photovoltaic systems could improve this performance.

Long Ye, Tianjin University, China, Ruijie Ma, The Hong Kong Polytechnic University, Kowloon, China, and colleagues have used the miscibility of binary blends as a guide to screen candidates for the second acceptor. Using this approach, they designed and synthesized the multifunctional small molecule acceptor BTP-2Br (pictured), which can improve the photovoltaic performance in both P3HT and PM6-based ternary OPVs.

A P3HT:ZY-4Cl:BTP-2Br ternary blend exhibited a record efficiency of 11.41 % for P3HT-based OPVs. According to the researchers, the simple approach they used can facilitate the selection of an optimal ternary combination with the desired morphology for fabricating efficient and cost-effective optoelectronic devices.

• Miscibility screening promotes the efficiency and stability of P3HT‐based organic solar cells,
  Kaihu Xian, Ruijie Ma, Kangkang Zhou, Junwei Liu, Mengyuan Gao, Wenchao Zhao, Miaomiao Li, Yanhou Geng, Long Ye,
  Aggregate 2023.
  https://doi.org/10.1002/agt2.466