Enhancing the Spectral Response of Mesoporous ZnO Films of Dye-sensitized Solar Cells by Incorporating Metal-free Organic Sensitizer and N719 dye

To enhance the spectral responses of the dye-sensitized solar cells (DSSCs), utilizing two or more dyes with complementary absorption spectra is a feasible way to absorb light in various regions of the solar spectrum. The organic dye, J1 dye, is self-synthesized for the first time, which shows a high absorption coefficient of 38,500 M^-1 cm^-1 and an absorption spectrum ranged from 400 to 600 nm. By co-sensitizing the J1 dye with the commercial N719 dye, the absorption region of the J1/N719 dyes can be extended to 700 nm, which nearly covers all the visible region of the solar spectrum. A light-to-electricity conversion efficiency (η) of 4.67% is achieved for the co-sensitized DSSC, which is higher than those of the cells sensitized with individual J1 dye (3.26%) or N719 dye (3.27%), probably due to the enhanced light absorption and more complete coverage of the small organic J1 dye on the ZnO surfaces for the co-sensitized DSSC. The ultraviolet-visible (UV-vis) absorption spectra and the incident photon-to-current conversion efficiency (IPCE) measurement are also utilized to analyse the wavelength-dependent light-to-electricity efficiency of the DSSCs.