Effect of TiO2 nanoparticle content in sol–gel derived TiO2 paste on the photovoltaic properties of TiO2 photoanode of dye-sensitized solar cells

In the present work, the effect of the amount of TiO2 nanoparticles, added to the sol–gel derived paste, on the photovoltaic properties of fabricated dye-sensitized solar cells (DSSCs) was investigated. A titanium sol (Ti-sol) was synthesized using a Pechini type sol–gel method, and different pastes were prepared by adding various amounts of TiO2 nanoparticles to the obtained Ti-sol. The pastes were used to fabricate the mesoporous TiO2 semiconducting layers for DSSCs. It was observed that by increasing the mass ratio (MR) of TiO2 nanoparticles to Ti-sol the thickness of TiO2 layer increases. This led to the more adsorption of dye molecules per unit area of active TiO2 layer, which were determined by UV–vis spectrophotometry. Also, micro-cracks were observed in TiO2 layers obtained from pastes with low MR values. But their amount and size decreased with increasing MR, which was due to the decrease of paste surface tension (σ). As a result, short circuit current density (Isc) showed continuous increase with increasing MR, which was due to the more dye adsorption. Open circuit voltage (Voc) first increased and then decreased by enhancing MR, which was explained by considering the electron–hole recombination rate. Finally, the DSSC fabricated from the paste with MR=0.65 showed the maximum conversion efficiency (η).