First evidence of electrode reconstruction in mesoporous NiO after operation as photocathode of dye-sensitized solar cells

For the first time it is shown that the NiO films operating as photocathodes in dye-sensitized solar cells (DSCs), alter their X-ray diffraction (XRD) pattern upon occurrence of the photoelectrochemical reaction of reduction. In particular, it has been observed that mesoporous NiO sensitized with Fast Green (FG) presents splitting and broadening of its characteristic XRD peaks after device operation in p-type DSC (p-DSC) and tandem DSC (t-DSC). The nature of the changes in the diffraction pattern of NiO does not vary with the magnitude of the current passing through the p-DSC and the t-DSC with NiO photocathodes. Such a combination of facts would indicate that the photoelectrochemical process of holes photoinjection mediated by the sensitizer is responsible of the structural variations in NiO photocathode. At a microscopic level, we attributed such modifications to the reconstruction of the NiO electrode following the realization of the dye-mediated process of electron transfer with lattice deformation possibly due to the inclusion of the chemisorbed sensitizer in the oxide structure. This observation opens up a completely new direction of research in the field of DSC and analogous devices as far as the analysis and the understanding of the interactions dye/semiconductor in the common operative conditions of a DSC are concerned.