Promotion of charge transport in low-temperature fabricated TiO2 electrodes by curing-induced compression stress

Abstract

In low-temperature fabricated dye-sensitized solar cells, promotion of the interparticle electronic connectivity, reduction of the trapping/detrapping events, and suppression of charge recombination on the semiconductor–electrolyte interface are key steps to improve charge collection and energy conversion efficiency. In this work, a new method based on curing cementing material (Ca(OH)2) under CO2 ambient to produce uniform CaCO3 coatings on mesoporous TiO2 nanoparticulate films is presented. The volume shrinkage resulting from the phase conversion of calcareous coating during the curing procedure can produce strong strain on the TiO2 electrode. By virtue of the compression stress, the interparticle electronic connectivity was promoted and the density of electronic states in the bandgap of the semiconductor was reduced. Thus, the electrode with CaCO3 coating exhibits better performance for diffusion and collection of electrons. Moreover, the formed CaCO3 coatings can also prevent the electrons from recombination on the semiconductor–electrolyte interface. In combination with a platinized electrode and electrolyte, the photovoltaic devices with CaCO3 coated electrode achieved an energy conversion efficiency of 4.79%, which is 40% higher than that of the cell with blank electrode.