Formation of double-layered TiO2 structures with selectively-positioned molecular dyes for efficient flexible dye-sensitized solar cells

•A novel flexible dye-sensitized solar cell, selectively loading two different dyes in discrete layers, was successfully formed on a plastic substrate.•η of the flexible tandem cell obtained by transferring the high-temperature-processed TiO2 layer was enhanced from 2.91% to 6.86%.•Interface control between two TiO2 layers is crucial for the efficient transport of photo-injected electrons from the top to bottom TiO2 layer.

To fabricate flexible dye-sensitized solar cells (DSCs) utilizing full solar spectrum, the double-layered TiO2 films, selectively loading two different dyes in discrete layers, were formed on a plastic substrate by transferring the high-temperature-processed N719/TiO2 over an organic dye (TA-St-CA)-sensitized TiO2 film by a typical compression process at room temperature. It was found that interface control between two TiO2 layers is crucial for the efficient transport of photo-injected electrons from the N719/TiO2 to the TA-St-CA/TiO2 layer. Electron impedance spectra (EIS) and transient photoelectron spectroscopic analyses exhibited that introduction of a thin interfacial TiO2 layer between the two TiO2 layers remarkably decreased the resistance at the interface, while increasing the electron diffusion constant (De) by ∼10 times. As a result, the photovoltaic conversion efficiency (η) of the flexible tandem DSC was 6.64%, whereas that of the flexible cell derived from the single TA-St-CA/TiO2 layer was only 2.98%. Another organic dye (HC-acid), absorbing a short wavelength region of solar spectrum, was also applied to fabricate flexible tandem DSC. The η of the cell derived from the HC-acid/TiO2 layer was only 2.91%, but that of the tandem cell obtained by transferring the high-temperature-processed N719/TiO2 was 6.86%.

Graphical abstractA novel flexible tandem dye-sensitized solar cell, selectively loading different dyes in discrete layers, was successfully formed on a plastic substrate by transferring the high-temperature-processed N719/TiO2 over an organic dye-adsorbed TiO2 film by a typical compression process at room temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide