Preparation of Nanocrystalline TiO2 Electrodes for Flexible Dye-Sensitized Solar Cells: Influence of Mechanical Compression

Nanocrystalline TiO2 electrodes were prepared using binder-free TiO2 paste on conductive ITO-PEN substrates by the doctor-blade method at significantly low temperature (140 °C), and the electrodes were further processed under different compressions (10–60 MPa) in order to improve interparticle connections and adhesion between the nanoparticles and the ITO-PEN substrate. TiO2 electrodes compressed at 30 and 40 MPa had relatively less cracks with low crack width. Electrode compressed at 30 MPa showed the highest internal surface area. Electrode prepared at this compression showed the best dye-sensitized solar cell (DSC) performance with Voc of 805 mV, Jsc of 9.24 mA cm–2, and an overall efficiency of 4.39%. Electrochemical impedance spectroscopy (EIS) studies of the sandwiched cells employing bare nanocrystalline TiO2 electrode and Pt counter electrode in I–/I3– electrolyte showed that electrode compression significantly influences the stability of the cells. EIS data suggested that degradation/corrosion processes may take place on ITO-PEN for sandwiched cells made by TiO2 electrodes compressed at all pressures. Thirty and 40 MPa compressions showed a minor degradation of ITO. The recombination dynamics at the TiO2/electrolyte interface were influenced by the changes in the nanostructured electrode internal surface area, changes in electron transport properties (due to improved sintering), and possible degradation/corrosion of ITO-PEN. Open-circuit voltage decay (OCVD) measurements showed that the DSC made by the 30 MPa compressed TiO2 electrode had the highest decay time, indicating low recombination properties, which is in a good agreement with other data