Thermal impact on (001) faceted anatase TiO2 microtablets and nanowalls's lattices and its effect on the photon to current conversion efficiency

Thermal annealing impact on the properties of (001) faceted anatase TiO2 with two different morphologies, i.e. microtablet (TMT) and nanowall (TNW), have been examined by observing the change in their lattice paramaters and photovoltaic properties when being subjected to several thermal annealing intervals, i.e. from 1 to 7 h, at 450 degrees C, under ambient atmosphere. The TMT and TNW were prepared on ITO substrate via liquid phase deposition method. The TMT is characterized by a squared tablet-like shape meanwhile the TNW is a squared-platelet morphology nanostructures. The XRD and Raman analysis indicated that both TMT and TNW underwent a lattice expansion with the increasing of the annealing interval. For example, the Raman results indicates that the main Raman character of E-g, i.e. O-Ti-O bridge bending oscilation, as well as B-1g and A(1g), i.e. Ti-O strain oscilation, blue-shifted with the increasing of the thermal annealing duration. However, the expansion is approximately 1.4% higher in TNW compared to TMT. Regarding the surface chemistry activity, it is higher on the TNW and it increases with the increasing of thermal annealing impact. Meanwhile, the TMT showed a tendency to steadily decrease in its surface chemistry activity with the increasing of the thermal annealing impact. The modification in the lattice parameters and the surface chemistry activity have effectively modified the TMT and TNW's photovoltaic performance. In typical process, the power conversion efficiency improve from 1.8% to 3.2% for DSSCs utilizing TMT and 1.5%-3.0% in TNW when the thermal annealing impact was increased. In general, the TNW exhibits relatively higher electrical and optical properties stability compared to TMT that is indicated by a small variation in the PCE value when the thermal impact further increased up to almost double above the optimum condition.