Effect of Annealing on Material Properties of Both Electrodes in Dye Sensitized Solar Cell Structure

Abstract

In dye sensitized solar cell structure, the transparent electrodes of tin oxide doped fluorine (SnO2:F) was coated by titanium dioxide (TiO2) and platinum (Pt) for cathode and anode electrodes, respectively. In order to achieve high efficiency solar cell, both electrodes are required to have proper crystal structure size and morphology. These can be modified during the annealing process therefore the effects of electrode annealing on their crystal structure and surface modification were investigated in this study. Thick films of TiO2 and Pt were deposited by screen printing method on 3mm thick glass substrate (Nippon Sheet Glass) coated with 500nm thick SnO2:F. The glass substrate has sheet resistance of 20 ohm/square with the optical transmission of about 70%. The mixed TiO2 powder has the diameter of about 20 nm. The screen print structure was heated for drying in the oven at 150oC for 1 hour. Then the TiO2 thick films were annealed at various temperatures from 400 to 550oC for 2 hours, while the Pt films were annealed at lower temperature from 300 to 500oC. The obtained thickness of TiO2 and Pt film after annealing become about 10 and 3 µm, respectively. The crystallinity of the films was examined by x-ray diffraction while the surface morphology of both films was determined by atom force microscopy. To investigate the relation between material structure and the performance of the solar cell, the annealed electrodes at different temperature were used to fabricate the dye sensitized solar cell structure with standard rutherium(II) (N719) dye and then the current voltage characteristic was measured under light with air mass of 1.5. It found that the structure with higher anneal temperature electrode exhibited higher power conversion efficiency originating from the higher short circuit current density of better crystallinity and higher surface area.