Optimization of fabrication parameters for efficient dye-sensitized solar cells based on dyes containing benzothiadiazole, indoline, and their co-sensitization

Fabrication of dye-sensitized solar cells (DSSCs) based on metal-free dyes including benzothiadiazole (RK1) and indoline (D205) was optimized in terms of TiO2 composition, solvent type, sensitization time, utilization of co-adsorbent and co-sensitization. It was found that methanol and tetrahydrofuran are the optimal solvents for fabricating the DSSCs based on RK1 and D205, respectively. Under the optimized conditions, the DSSC based on D205 made from transparent/mixture TiO2 photoanode exhibited a power conversion efficiency (PCE) of 5.76%, while RK1-based DSSC with transparent/scattering TiO2 achieved a PCE of 8.43%. The utilization of different photoanode compositions for each dye can be explained by the difference in size or geometry of these dyes. A stepwise co-sensitization strategy was further applied to improve the performance of the DSSCs. The co-sensitized solar cell based on the two dyes shows a panchromatic spectral response in the range of 360-670 nm and gives an overall PCE of 9.30%, which is superior to that for RK1-sensitized solar cells.