In recent years, the optimization of the morphology has become a key issue for further improving the energy conversion efficiency of polymer solar cells, although the adjustment of the crystallization behavior and phase area of ​​the acceptor by the binary mixed solvent (usually the main solvent and additive composition) has been achieved. Good results, but it is also incapable of regulating finer morphological parameters such as the purity of the phase zone and the adjustment of the phase zone interface.
Under the strong support of the Chinese Academy of Sciences, the Ministry of Science and Technology, and the National Natural Science Foundation of China, the State Key Laboratory of Polymer Physics and Chemistry at the Institute of Chemistry has recently made important progress in the method and mechanism for the regulation of the microscopic morphology of the active layer of polymer solar cells.
For the first time, the researchers introduced a ternary mixed solvent to systematically study the surface topography, bulk phase area, and crystallization behavior of polymer solar cells based on PDPP3T and PC71BM (see Figure 1) and with North Carolina State University (North Carolina). Researchers at the Department of Physics of the State University cooperated to analyze the active layer of a polymer solar cell from a single solvent to a ternary mixed solvent to acceptors using a series of methods such as resonant soft X-ray diffraction and two-dimensional grazing incidence wide-angle X-ray diffraction. The evolution of appearance.
Figure 1 Materials and device structures of polymer solar cells
Through system variable adjustment, it was found that when the ratio of ternary mixed solvent is DCB/CF/DIO = 76:19:5 (v/v), the crystallinity is the best, the size of the phase zone is small, the purity of the phase zone is the highest, and the phase zone interface is the highest. Roughness (as shown in Figure 2) results in an energy conversion efficiency of 6.71%, which is one of the highest efficiencies of current single-layer batteries based on DPP-like materials. At the same time, their research shows that PDPP3T is a promising red-absorbing material (λedge>900 nm, VOC>0.65 V, PCE>6%), and is expected to be used in the construction of efficient stacked devices.
Fig. 2 Evolution of acceptor morphology from monosolvent to ternary solvent
This research is the first example of successful introduction of a ternary mixed solvent into the preparation of polymer solar cells, revealing that the rational choice of solvent system has an important impact on the performance of the device, and also provides a device optimization for high-efficiency materials. New way.
The results of the study were published in the "Advanced Materials" (Advanced Materials, 2012, 24, 6335-6341). After the work was published, it was reported by the famous science website Science Daily about How Solvent Mixtures Affect Organic Solar Cells Structure.
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