Benefits of dispersion solvents with more OH groups in electrospray preparation of TiO₂ photoelectrode for the improvement of DSSC performance

TiO₂ anode prepared by electrospray (ES) method using dispersion solvents of ethylene glycol (EG) or glycerol enhanced the performance of dye-sensitized solar cells (DSSCs) compared to the conventional solvent of ethanol. TiO₂ dispersion in EG or glycerol were found more stable as demonstrated by dynamic light scattering (DLS) experiments. Infrared spectra (IR) revealed that dispersion solvent with more hydroxyl (OH) groups could interact with TiO₂ more effectively, leading to higher stability of TiO₂ suspension, and enabling higher TiO₂ concentration, which are beneficial to mass production by utilizing stable suspension as well as reducing deposition time. When ethanol is used as dispersion solvent, the nozzle is often clogged by TiO₂ block due to fast evaporation of ethanol at the nozzle tip. When EG and glycerol are used, this problem does not appear because of their nonvolatile nature. In addition, higher conductivity of EG and glycerol also helps to generate smaller droplet in ES process, thus more uniform TiO₂ films is expected. Scanning electron microscope (SEM) study showed that while hierarchically structured TiO₂ (HS-TiO ₂) spheres were formed in TiO₂ anode by ES deposition using any one of three solvents, the secondary grain sizes of TiO₂ in the EG and glycerol based anodes were bigger. As a result, better DSSC performance was achieved based on TiO₂ anode prepared by ES procedure using dispersion solvent of glycerol under high TiO₂ concentration.