An investigation of the effect of high-pressure on charge transfer in dye-sensitized solar cells based on surface-enhanced Raman spectroscopy

The interfacial charge transfer (CT) that plays an important role in enhancing the photoelectric conversion efficiency of dye-sensitized solar cells (DSSCs) has not always been fully explored. Here, TiO2@N719@Ag DSSCs system was constructed, and the CT processes have been monitored by surface-enhanced Raman scattering (SERS) spectra. Meanwhile, it is well known that as one of the most common external stimulis, high pressure can increase the free carrier density of TiO2 NPs and cause the band gap to narrow. In the high pressure SERS experiment, we observed a significant enhancement of N719 dye in the TiO2@N719@Ag system up to 2.48 GPa, which is consistent with the variation trend of charge transfer degree (ρCT). It is indicated that band gap changes will strongly affect the CT process, further influence the SERS signal intensity (or ρCT), and thus increase the CT probability of DSSCs. Futhermore, the decoration of Ag NPs in the TiO2@N719@Ag DSSCs system can introduce localized surface plasmon resonance (LSPR), enhance the light trapping ability and offer additional CT pathways. Importantly, it is possible to improve the photoelectric conversion performance of DSSCs via high pressure method and the introducing of Ag NPs. Finally, in order to observe the CT process of DSSCs more clearly, the models describing the CT mechanism have been proposed. SERS spectroscopy is expected to be a promising technique for the exploration of the interfacial CT behavior in DSSCs devices, which may further broaden the thoughts of improvement of efficiency of cells.