Organic solar cells are formed by the blending of organic semiconductor electron donors and acceptor materials, which are easy to prepare, flexible and flexible, and suitable for mass production, giving them a bright future. At present, although the highest efficiency of organic solar cells has exceeded 12%, the relatively low energy conversion efficiency and stability problems are still the main bottlenecks restricting its commercialization. The design of new materials and the optimization of multi-level topography are the main strategies to solve the above problems. Among them, the control of multi-level structure distribution is particularly difficult. Because multi-level structures are influenced by the choice of pair of donor and acceptor materials. Xi'an Jiaotong University researchers from the acceptor and donor materials, respectively, two different directions as a starting point, the successful access to a multi-level distribution of the control methods and access to the receptor, the general law of pairing.
In the receptor materials, the State Key Laboratory of Metal Materials Strength, Xi'an Jiaotong University Professor Ma Wei and the Hong Kong University of Science and Technology Professor Yanhe cooperation, through the adjustment of molecular structure designed a pair of heterogeneous donor polymers: strong crystalline PTFB -P and weakly crystalline PTFB-O. By blending with the fullerene acceptor and the non-fullerene acceptor, respectively, it was found that higher conversion efficiency can be obtained when the small non-fullerene acceptor is blended with the less crystalline donor; and fullerenes Receptors exhibit better performance when blended with more crystalline donors. The law also affects the evolution of multi-level structure. Non-fullerene based organic solar cells based on the novel donor polymer (PTFB-O) achieved a high conversion efficiency of 10.9%. This result provides an extremely important insight, reference, and guidance for the design of donor polymers for non-fullerene organic solar cells. The research is published in Nature Communications, entitled "Donor polymer design enables efficient non-fullerene organic solar cells." Xi'an Jiaotong University for the work of the first correspondent units.
At the same time, in the aspect of donor materials, the group of Professor Ma Wei and the research team of researcher Wei Zhixiang of the National Nanoscience Center cooperated with each other to design three novel small-molecule donors BTID-0F, BTID-1F and BTID -2F, and it was observed that it has excellent properties when it is complexed with a fullerene acceptor. Detailed structural analysis showed that molecular fluorination improved the multi-layer morphology of active layer (including the increase of phase purity, the formation of hierarchical structure and longitudinal distribution, etc.) and achieved a high conversion efficiency of 11.3%. This efficiency is the highest value of the organic solar cell of small molecule fullerene system. The work is also published in Nature Communications by Xi'an Jiaotong University as co-author of the article.
These two studies have been supported by the "National Key Research and Development Program" of the Ministry of Science and Technology, the National Natural Science Foundation of China, the Young Top PoE Program Fund of Xi'an Jiaotong University and the time support provided by the Berkeley National Laboratory.
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