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Tham khảo tài liệu 'solar cells dye sensitized devices part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 292 Solar Cells - Dye-Sensitized Devices There are mainly two effects affecting IPCE when we illuminate with different power density conditions the trap filling effect and the electrolyte ions mobility. While the first affects negatively the IPCE spectra at low light level conditions the second comes into play at high light density reducing the solar cell response as well. For trap filling we mean the ability to occupy the states inside the titanium dioxide gap close to the conduction band edge. These levels are centers of recombination for the electron in conduction band. At single wavelength the filling is not efficient reducing the cell response see Fig. 8 . It has been verified that the application of a bias light can be simulated in the DC method if the intensity of the monochromatic light is high Sommeling et al. 2000 . On the other hand at high intensity the electrolyte ions could be not able to regenerate effectively the homo level of the dye. This effect is dramatically enhanced when we use Co II -Co III as redox couple. Aware of the dependence from light intensity to control the measurement accuracy under solar simulator it is mandatory to perform IPCE acquisition at the same conditions. Different dynamics are present in the photovoltaic mechanism of a dye solar cell. In presence of illumination however only the slowest process will dominate. The result is that the dye solar cell response is really slow. The modulation of the monochromatic light should be less than 1 Hz taking into account that it should be verified every time different materials are involved in particular the electrolyte and the titanium dioxide film employed . Fig. 9. IPCE spectra in function of the bias light illumination for a dye solar cell with Co II -Co III as redox couple. A decrease of the signal intensity at high intensity levels has been measured. Dye Solar Cells Basic and Photon Management Strategies 293 0 -2 -4 -6 -8 -10 1 10 100 frequency Hz Fig. 10. DSC response in function
