Densely packed zinc sulfide nanoparticles on TiO2 for hindering electron recombination in dye-sensitized solar cells

We report new types of TiO2@CdS and TiO2@ZnS binary structures fabricated by decorating TiO2 surfaces with CdS or ZnS nanoparticles. The material characterization shows that the presence of CdS on the TiO2 surface results in a red-shift of the material band edge in the visible region compared to pure TiO2. A further enhancement of visible light was achieved by N719 dye loading on TiO2@CdS. The binary structure electrode with TiO2@ZnS-4 extended the absorption edge to the visible region and was used as an efficient photo-anode in dye-sensitized solar cells (DSSCs). The experimental results indicate that replacing Ti2+ with Zn2+ ions on the surface greatly increases the surface stability compared to TiO2. Furthermore, Zn and S impurities have a drastic impact on the host material and can create new energy states that can delay the exciton recombination and allow charge separation. The DSSCs based on the TiO2@ZnS-4 photo-anode achieved a power conversion efficiency (PCE) of 4.91% under one sun light illumination, which is higher than those of bare TiO2 (2.84%) and TiO2@CdS-4 (1.44%). This work demonstrates a promising way to design efficient photo-anodes for use in DSSCs that can achieve a high PCE with a lower recombination rate during electron transportation.