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Figure 1 Molecular structure of the polymer and related photovoltaic performance parameters
Introducing a fluorine substituent on the acceptor unit of the DA conjugated polymer can effectively reduce the HOMO energy level of the polymer without affecting the absorption spectrum and the mobility of the polymer, thereby increasing the open circuit voltage and the photovoltaic performance of the device. , has become a research hotspot in recent years; but limited by the selectivity of the acceptor unit in the introduction of fluorine substituents, this method can only be applied to a small number of polymer photovoltaic material systems, and therefore, how to effectively expand its polymerization The application of photovoltaic materials system has a very important scientific significance.
With the strong support of the Chinese Academy of Sciences, the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Institute of Chemistry, researchers from the State Key Laboratory of Macromolecular Physics and Chemistry of the Institute of Chemical Physics for the first time proposed conjugated side chains on DA conjugated polymer donor units. The design idea of ​​fluorine substituents was introduced, and a method for synthesizing fluorine substituents on the conjugated side chain of polymer donor units was developed (Patent Application No. 4), and a series of polymer photovoltaic materials (Adv. Mater) was designed and synthesized. ., 2014, 26, 1118-1123).
The results show that the absorption spectrum and mobility of the polymer have almost no change after the fluorine substituent is introduced, and the HOMO energy level of the polymer is obviously decreased. Compared to the introduction of fluorine substituent on the acceptor unit, the conjugated side chain on the donor unit The introduction of a fluorine substituent can more effectively reduce the HOMO energy level of the polymer; under the synergistic effect of fluorine substituents on the acceptor unit, the HOMO energy level of the polymer decreases by 0.30 eV; the open circuit voltage of the corresponding photovoltaic device increases by 0.22V. , The energy conversion efficiency increased from 4.5% to 8.6%.
The results of this study break through the limitations of the fluorine substituents in the adjustment of the energy levels of polymer molecules. For the first time, the design concept of introducing strong electron-withdrawing groups on the donor units to adjust the energy levels of the polymer molecules has been successfully achieved. The molecular design of photovoltaic materials provides new ideas and methods, which will greatly promote the development of new high-efficiency polymer photovoltaic materials.
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