| Polymer solar cells have received considerable attention because of their easy processing,low cost and availability of fabrication on flexible substrates.However,the carrier mobility of the organic active layer in polymer solar cell is lower than that of inorganic semiconductors,which limits the thickness of the active layer.The active layer thickness of the polymer solar cell is usually below 200 nm,which makes it difficult for the incident light to be completely absorbed by the active layer.The light absorption of the polymer solar cells is much lower than that of silicon solar cells,which is nearly 100%.How to further enhance the light absorption of the active layer and improve the photoelectric conversion efficiency of the device is one of the research hotspots in the field of polymer solar cells.In order to solve the problems,two kind of light-trapping structure in the cathode buffer layer of polymer solar cells are proposed in this paper.Firstly,a double-layer Zn O film was prepared by conventional and rapid thermal annealing respectively to obtain a cathode buffer layer with light-trapping effect.The incident light is refracted and scattered at the surface of film,this effect increases the optical path in the active layer,enhances the light absorption in the active layer and improves the photoelectric conversion efficiency of the polymer solar cells.Secondly,we explored the influence of the hydrothermal synthesis of Zn O nanorod with different fabrication parameters on the light absorption of active layer in polymer solar cells.Finally,we used Cs doping to improve the crystal quality of Zn O nanorod and the electrical properties of the Zn O nanorod cathode buffer layer.The specific content is as follows:We firstly prepared a double-layer Zn O light-trapping structure by conventional and rapid thermal annealing respectively as the cathode buffer layer.We explored the optimal annealing temperature and time and the results show that,in the condition of 500 ℃ and 40 s,the light-trapping effect in the device is most significant and the light absorption of active layer is highest.The polymer solar cells with the structure of ITO/double-layer Zn O light-trapping structure/P3HT:PC61BM/Mo O3/Ag were also prepared and the photoelectric conversion efficiency of the device reaches 3.54%,which is 45.7% higher than that of the single-layer Zn O device using conventional thermal annealing.Then,we used the hydrothermal synthesis method to grow the Zn O nanorod cathode buffer layer,and explored the optimal growth time.When the growth time is 10 min,Zn O nanorod cathode buffer layer shows the best light-trapping effect and the absorption of active layer is highest,which is 6.7% higher than that of the device with double-layer Zn O structure.After that,we prepared the polymer solar cells with the structure of ITO/Zn O nanorod /P3HT:PC61BM/Mo O3/Ag and the photoelectric conversion efficiency of the device reaches 3.05% when the growth time is 10 min.In order to improve the crystallinity and electrical conductivity of the Zn O nanorod cathode buffer layer,we doped the Zn O nanorod array with Cs and explored the optimal Cs doping concentration.When the doping concentration is 1m M,the photoelectric conversion efficiency of the device is the highest,reaching 3.24%.Compared with that of the undoped device,the efficiency of the device is increased by 6%.In this paper,we first prepared a double-layer Zn O light-trapping structure using conventional and rapid thermal annealing respectively as the cathode buffer layer of polymer solar cells.Then we prepared Zn O nanorod as cathode buffer layer with light-trapping effect by hydrothermal synthesis.Both structures improve the light absorption of the active layer and the photoelectric conversion efficiency of polymer solar cells.The proposed light-trapping structures are easy processing and low cost,which provide a new idea for the fabrication of high efficiency polymer solar cells and have a good application prospect. |
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