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Introduction to polymer solar cells

by:dcfpower     2021-04-01
u003cpu003e People's research on polymer solar cells can be traced back to the 1980s. In 1977, AJ Heeger and H. Shirakawa mixed polyacetylene with a small amount of iodine, and the resultant material was more conductive than pure polyacetylene. Increased 108 times, close to the level of good conductors such as silver and copper. Next, some major discoveries appeared one after another: In 1986, Dr. Qingyun Deng of Kodak in the United States made an organic solar cell based on a heterojunction. In 1992, Heeger and others of the University of California, Santa Barbara discovered polymer materials. The exciton dissociation with fullerene acceptors provides a basis for the development of polymer heterojunction solar cells. u003c/pu003eu003cpu003eIn 1995, a bulk heterojunction solar cell based on a polymer-donor-acceptor blend structure was independently developed by Friend and others from the University of Cambridge and Heeger and others from the University of California, Santa Barbara. So far, although there is a big gap between the application and silicon-based solar cells, the basic structure of polymer solar cells has been determined, and has been rapidly developed in the next 20 years. u003c/pu003eu003cpu003eu003cpu003e Recently, Liao et al. of Tsinghua University in Hsinchu, Taiwan, with a new type of polymer battery based on PTB7, refreshed the highest energy conversion efficiency of single-junction polymer solar cells in public reports to 9.35% New record. In recent years, more efforts to commercialize organic solar cells have focused on simplifying the manufacturing process, enhancing the stability of the device and the service life in different regions and environments [7]. For organic solar cells, the rapid development in recent years has aroused people's keen interest in the highest possible efficiency of this system. As early as 1961, Shockley and Queisser proved through theoretical studies that the limit value of the energy conversion efficiency of inorganic semiconductor solar cells is about 30%. By adopting methods such as multi-junction and concentrating forms, the actual efficiency of inorganic solar cells is very close. This value. One of the main differences between organic solar cells and inorganic solar cells is that organic solar cells produce tightly bound excitons (electron-hole pairs), which is the lower dielectric material of the active layer in organic solar cells. Caused by constants. Such tightly bound excitons are called Frenker excitons, and their binding energy is usually between 0.3-1 eV. Such a large binding energy prevents excitons from ionizing under the action of an electric field. For organic electroluminescence devices, this phenomenon reduces the probability of excitons entering the non-radiative attenuation orbit and ensures the high efficiency of electroluminescence. For organic solar cells, this makes the photoelectric conversion process an additional step compared to inorganic solar cells. Therefore, there is a certain energy loss during the separation of photogenerated excitons in organic solar cells, which is generally 0.3-0.4 eV. This characteristic makes researchers generally believe that the theoretical maximum efficiency should be lower than that of inorganic solar cells. It is generally believed that the energy difference between the lowest unoccupied molecular orbital (LUMO) of the donor and the highest occupied molecular orbital (HOMO) of the acceptor in the heterojunction is the driving force for the dissociation of Frenkd excitons. The factors that really limit the efficiency of organic solar cells seem to be very simple, but they are actually very complicated. It is necessary to conduct an in-depth discussion on this issue. u003c/pu003eu003cpu003eu003cpu003eu003c/pu003eu003c/pu003eu003c/pu003eu003c/pu003e
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