Evaluation of Optical Properties of Dye-sensitized Solar Cell Incorporating Mesoscopic Interfacial Roughness

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Dye-sensitized solar cell (DSC) has usually a laminated structure. Optical energy loss due to the reflection at the interface is inevitable because of the difference in the intrinsic refractive index between mediums. The accumulation of these losses results in the considerable amount of the decrease of photo-electric conversion efficiency. In this study, the effect of mesoscopic interfacial rough-structure has been examined in a sense of optical impedance-matching due to the gradient-refractive index caused by the surface roughness.The structure concerned in a DSC is "air/ glass/ transparent conductive film (ITO electrode)/ dye adsorption TiO_2 film" and "Pt counter electrode". ITO and Pr films are prepared by the rf sputtering method. Optical properties of the specimens were measured using an ultraviolet-visible-near infrared spectrometer in the wavelength (λ) range of 0.24-2.60 μm. Surface morphology was observed using an atomic force microscope (AFM). Based on these observed data, the simulation of finite-difference time-domain (FDTD) method has been performed in a range of λ=0.4-1.0μm. The reductions of 3.6%, 0.5% and 0.5% in reflectance of respective roughened interfaces of air/ glass, glass/ ITO and ITO/ dye adsorption TiO_2 have been estimated. The roughened Pt film showed large diffusive reflectance.In this study, it has been confirmed that the suitable roughness is useful for the depression of reflectance at the interfaces in the DSC.