An electron acceptor is a substance that accepts electrons in electron transport. So far, in the field of organic photovoltaic cells, a large number of researchers have devoted themselves to the study of electron donor materials, but the research progress of acceptor materials lags far behind that of electron donor materials. In recent years, it has become increasingly difficult to improve the efficiency of organic solar cells, suggesting that simply finding new electron donors will not improve the efficiency of cells significantly. In addition, significant breakthroughs in the photoelectric conversion efficiency of organic solar cells are closely related to the research of new donor/acceptor materials.
Fullerenes are closed caged molecules consisting of different numbers of non-planar five-membered and six-membered rings. It belongs to electron-deficient alkene, and its three-dimensional conjugated electronic structure makes it have good electron acquisition ability and photoelectric transmission performance, so it is often used as acceptor materials for organic solar cells. In the classical C60 fullerene structure, the absorption of PC71BM and PC84BM prepared by C71 and C84 is significantly stronger than that of PCBM in the visible region, and the photoelectric conversion efficiency is also enhanced compared with that of PCBM. Therefore, at present, the electron acceptor materials used in polymer solar cells with photoelectric conversion efficiency exceeding 7% all use the Fullerian derivative PC71BM.
Perylene diimide and its derivatives were highly absorptive in the visible region and had high light and thermal stability, so they were initially used as organic functional dyes on a large scale. Later, it was found that perylene diimide molecules had a large π-π conjugate structure, Therefore, its molecules have high electron mobility and electron affinity potential. Based on the above characteristics, perylene diimide became a popular type of electron acceptor material in the field of photoelectric materials. However, based on the above characteristics, the solubility of perylene imide was relatively low in common solvents. As an important electron acceptor material, perylene imide and its derivatives were far from PCBM, but they played an important role in high efficiency organic photovoltaic cells.
Dithiophene (pyrrole and pyrrolidone) (DTDPP) itself contains D-A structure, and its derivatives (small molecules and polymers) are A class of bipolar semiconductor materials with excellent performance, which can be used as electron donor materials and electron acceptor materials under the condition of appropriate energy levels. It has played an important role in polymer solar cells. DPP-based polymers are also a popular class of donor materials in bulk heterojunction cells.
Conjugated polymers are also one of the more studied acceptor materials in organic solar cells. Its advantage is that it has good compatibility with the donor polymer and can form a large interpenetrating network structure with effective interface separation, which enhances the photon enrichment efficiency and plays an important role in improving the efficiency of solar cells.