Effect of sol–gel ZnO spin-coating on the performance of TiO2-based dye-sensitized solar cell

• ZnO sol–gel layers of different ZnO amounts were spin-coated on TiO2 electrodes.
• The corresponding DSSCs were characterized and compared to the bare TiO2–DSSC.
• The optimum ZnO sol amount for maximum DSSC efficiency is 1 drop at 0.1–0.2 M.
• The created energy barrier enhances η by reducing electron back-recombination rate.
• The reduction of dye-adsorption efficiency of TiO2 due to ZnO screening decreases η.

Dye-sensitized solar cells (DSSCs) with ZnO spin-coated TiO2 electrodes are compared to a DSSC with a bare TiO2 electrode. It is demonstrated that the ZnO of controlled amount, by varying the number of sol drops and the precursor concentration during coating, can indeed enhance the performance of the DSSC. The maximum DSSC efficiency is obtained with a single sol drop at a precursor concentration between 0.1 M and 0.2 M, with an enhancement of over 100%. In the light of measured optical absorption spectra of the different films and desorbed dye solutions, the results are interpreted in terms of two competing factors: The formation of an energy barrier which increases the photocurrent by reducing the rate of interfacial electron back-recombination and the reduction of the dye-adsorption efficiency of the TiO2 film with increasing ZnO amount in the coating ZnO layer.