Investigation On The Enhancement Of Conversion Efficiency Of Solar Cell

Crystalline silicon solar cells are facing a challenge of how to improve their energy conversion efficiency. Among the factors that limit the performance of the solar cells, the poor spectral response in short wavelength range play an important role. The high reflection and short penetration depth of short wavelength photons make it difficult to generate electron-hole pairs inside the cells. One way to solve the problem is to introduce down conversion effect to convert short wavelength photons to longer wavelength photons.YAG:Ce, a kind of rare earth luminescent material, is widely used in the LED industry and has the down conversion effect. In the thesis, we have applied YAG:Ce as the down conversion materials on monocrystalline silicon solar cells and investigated the fabrication of YAG:Ce phosphors and thin films, influences of the phosphors and thin films on the cells.YAG:Ce phosphors were prepared by using high temperature solid state reaction method. XRD analysis showed that the phosphors have good crystallinity and can convert the photons with wavelength below 480 nm to the photons with wavelength above 500 nm. The quality of YAG:Ce thin films made by sputtering can be improve through high temperature annealing process. The comparison of the transmissions between YAG:Ce thin films with different thicknesses gives the way to get suitable thin films for the monocrystalline silicon solar cells.Spin-coating method is used to deposit directly YAG:Ce phosphor particles on the surface of the monocrystalline silicon solar cells, and the spectral response in ultraviolet and blue ranges has been improved. In the range from 200 nm to 500 nm, the number of light generated carries increases by 8.31%, and in the range from 200 nm to 1100nm, the number of light generated carries increases by 1.15%。The conversion efficiency of the solar cells rises from 15.30% to 15.46%。Th introduction of YAG:Ce phosphors brings the effect of down conversion and the rise of surface reflection. Two mechanisms determine the small improvement of the solar cells.To reduce the surface reflection, we have proposed a new structure of down conversion solar cells with low reflection. YAG:Ce thin films are deposited on the lower surface of a piece of quartz, and packaged with EVA films and solar cells for form a module. The conversion efficiency increases from 18.45% of the cells to 19.27% of the modules, a relative growth of 4.44%. The improvement is attributed to the down conversion effect of YAG:Ce thin films and the reduced reflection of the new structure in the short wavelength range.Surface plasmon is used to improve the fluorescence of YAG:Ce and the performance of the solar cells. Although it has been verified that the surface plasmon can promote the emission of YAG:Ce, due to the limitation of fabrication processes, the new structure of the solar cells is not good enough to give a better performance of the cells. This will be investigated in the future.