Flexible Polymer based Dye Sensitized Solar Cells Fabrication through High Temperature Sintering Processes

Abstract

In this study, a novel approach of heat sink assisted sintering has been investigated for increasing the sintering/processing temperature in the fabrication of flexible polymer (PET) DSSC photoelectrodes without changing polymer substrates stability and integrity. In this sintering process, TiO2 layer coated onto the ITO PET was heated to the higher temperature from top side, whereas concurrent cooling from the bottom PET layer of the substrate by heat transfer using a heat sink kept the polymer film without any deformation. Thus, the heat generated from a hot plate during TiO2 coated or bare ITO PET substrate sintering was quenched by the plate-fin heat sink equipped with a water pump driven coolant flow through the channels of the fins. A mixture of water and ethylene glycol (1:1 vol ratio) was used as a coolant, as this mixture was proven to exhibit higher thermal conductivity than pure ethylene glycol (EG) and lower freezing point than water. The electrical sheet resistance measured in the bare ITO PET samples sintered at 250 °C for 20 min also confirmed no major changes from its original resistance value measured at room temperature. Also, there were no visual cracks or peeling off in the TiO2 coated ITO PET substrates seen after the bending tests, indicated a good mechanical stability and adhesion between the TiO2 film and ITO PET substrate after the sintering. Transmittance of bare ITO PET heat treated at different sintering temperatures indicated that the optical transparencies of ITO PET substrates were also not affected until the sintering temperature reached 250 °C. FESEM surface topographic images of TiO2 film coated ITO PET confirmed that the TiO2 film formed was crack free, and a porous layer of well-connected TiO2 nanoparticles was formed on top of the ITO PET substrate. X-ray diffraction results showed an increase in peak intensities due to the raise in the crystallization of TiO2 films on ITO PET sintered at higher temperatures. The diffuse reflectance spectra results confirmed...