In recent years, solution-processable bulk heterojunction organic solar cells have developed rapidly. With the design concept of fused-ring electron acceptors, a series of high-efficiency acceptor materials have sprung up, with the highest efficiency exceeding 18%. However, the synthetic route of such materials is generally complicated and the overall yield is low. In order to solve the above problems, Professor Chen Hongzheng of Zhejiang University first proposed in 2018 to construct A−D−A'(D')−D−A non-fused ring electron acceptors with simple or low condensed aromatic units, thereby shortening the reaction time. route to reduce synthesis costs.

In order to enhance the coplanarity within the molecule, weak intramolecular forces, namely non-covalent conformational locks, are usually introduced into the design of such materials. This concept was first proposed by Professor Huang Hui and Professor Tobin Marks of Northwestern University (J. Am. Chem. Soc. 2012, 134, 10966.). At present, non-covalent "conformational locks" have been widely used in the design of conjugated small molecules and polymer materials, resulting in a series of high-performance organic semiconductor materials that can be used in organic solar cells and field effect transistors. It has gradually become one of the important strategies for designing high-performance organic semiconductor materials.

Recently, Huang Hui's team from the University of Chinese Academy of Sciences designed and synthesized a novel non-fused-ring electron acceptor BTzO-4F, which uses benzotriazole as the D' unit and contains a "conformational lock" of S O. Due to the wide absorption range and suitable energy level of this molecule, when it is blended with the donor polymer PBDB-T, it can respond with external quantum efficiency in the range of 300 to 900 nanometers, and has good excitation ion dissociation efficiency and microscopic morphology. The optimal device obtained an open-circuit voltage of 0.839V, a short-circuit current of 23.58mA cm-2, and a fill factor of 69.73%, achieving a photoelectric conversion efficiency of 13.80%. The highest record for conversion efficiency. This latest achievement further demonstrates the application potential of non-covalent "conformational locks", and also provides important new ideas for the design of non-fused ring electron acceptor materials.

The research work has been published online in Science China Chemistry. The co-first authors are PhD students Liu Xingzheng and Wei Yanan at the University of Chinese Academy of Sciences, and the co-corresponding authors are Dr. Zhang Xin and Professor Huang Hui. The above results were supported by the National Natural Science Foundation of China, the Key Research and Development Program of the Ministry of Science and Technology, and the Key Research Program of Frontier Science of the Chinese Academy of Sciences.

An A-D-A’-D-A type unfused nonfullerene acceptor for organic solar cells with approaching 14% efficiency
Xingzheng Liu, Yanan Wei, Xin Zhang, Linqing Qin, Zhixiang Wei, Hui Huang*
(https://engine.scichina.com/doi/10.1007/s11426-020-9868-8)