A new research strategy for determining the conduction band movement of TiO2 films and charge recombination between electrons in the TiO2 film and electron acceptors in the electrolyte was proposed. Steady-state short-circuit current density versus open-circuit voltage was employed to attain the exchange current density and recombination reaction order. Transient photovoltage decay and open-circuit voltage decay measurements were carried out to obtain the energetic distribution of trapped electrons. Reduced voltage-dependent trapped electron concentration and trapped electron concentration-dependent recombination current density were used to analyze influence factors of open-circuit voltage, including contributions from conduction band movement and charge recombination. The simulated and measured electron concentration were in agreement and confirmed the validity of this method for extracting conduction band movement and recombination parameters. This new approach provides a physical insight which could help us to more conveniently and efficiently understand the operation of DSCs.

Correlation between current–voltage curves and recombination kinetics of dye-sensitized solar cells was a key subject for understanding the operation mechanisms and improving the device performance. A galvanostatic constant intensity light perturbation (GCILP) technique carried out on the current–voltage curve was developed to discover the correlation. The technique focused on synchronously deriving recombination kinetics and energetic distribution of trap state from the photovoltage responses and reconstructing the current–voltage curve by these derived kinetic parameters. In this technique, the photovoltage response amplitude was analyzed to obtain recombination kinetic parameters such as equilibrium dark recombination current density (or exchange current density) and recombination reaction order; the photovoltage response time trace was used to determine energetic distribution of trap states. Based on these analysis results, not only the effects of conduction band shifts and changes in the recombination rate on the open-circuit voltage could be analyzed but also the current–voltage curves could be successfully reconstructed. So this technique provided a new more convenient approach for efficiently evaluating and deeply understanding the important characteristics of solar cells.

We investigate the dependence of the photovoltaic performance of dye-sensitized solar cells on the cations with different charge densities, such as lithium (Li+), sodium (Na+), potassium (K+), and dimethylimidazolium (DMI+). The efficiencies of light harvesting, electron injection and charge collection were evaluated to clarify the influence of cation selection on photocurrent generation. It is found that the short-circuit photocurrents of DSCs gradually diminish with decreasing cation charge densities, partially owing to reduced electron injection rates which are intimately related to the reaction Gibbs free energies. Further experiments indicate that the upward movement of conduction band edge results in decreased reaction Gibbs free energy of electron injection from Li+ to DMI+. At an irradiation of 100 mW cm−2AM1.5 sunlight, the open-circuit photovoltage and the fill factor of a typical dye-sensitized solar cell increase in the order of Li+ < Na+ < K+ < DMI+. Analyses of impedance data reveal that the increase of cell photovoltage mainly correlates with the upward shift of the conduction band edge induced by the adsorption of low-charge-density cations on the surface of titania nanocrystals. A J–V model was proposed to understand the improvement of the fill factor. It is found that the increase of the fill factor stems from the decrease of recombination current density under the equilibrium state in the dark by fitting the J–V data with the model.

For a sphere electrode enclosed in finite-volume electrolyte, the measured current will deviate from the result predicted by the semi-infinite diffusion theory after some time. By random-walk simulation, we compared this time to the one needed for diffusion layer to reach electrolyte boundary, and revealed a clear signal delay of electrochemical current. Further we presented a quantitative description of this delay time. The simulation results suggested that the semi-infinite diffusion theory can even be applied when the theoretical diffusion layer grows to 1.28 electrolyte thicknesses, with an accuracy better than 0.5%. We attributed this time delay to the molecules’ finite propagation velocity. Finally, we discussed how this delay can influence and facilitate the following electrochemical detection towards the nanometer and single-cell scale.

In this paper, based on Einstein relationship between diffusion and random walk, the electrochemical behavior of a system with a limited number of molecules was simulated and explored theoretically. The transition of the current vs time responses from discrete to continuous was clearly obtained as the number of redox molecules increased from 10 to 106. By correlation analysis between the simulation results and the results of analytical expressions, a quantized extent parameter was proposed to investigate the underlying rules of these discrete signals, which looked stochastic. The results revealed that this parameter would be useful to describe such systems.

A new research strategy for determining the conduction band movement of TiO2 films and charge recombination between electrons in the TiO2 film and electron acceptors in the electrolyte was proposed. Steady-state short-circuit current density versus open-circuit voltage was employed to attain the exchange current density and recombination reaction order. Transient photovoltage decay and open-circuit voltage decay measurements were carried out to obtain the energetic distribution of trapped electrons. Reduced voltage-dependent trapped electron concentration and trapped electron concentration-dependent recombination current density were used to analyze influence factors of open-circuit voltage, including contributions from conduction band movement and charge recombination. The simulated and measured electron concentration were in agreement and confirmed the validity of this method for extracting conduction band movement and recombination parameters. This new approach provides a physical insight which could help us to more conveniently and efficiently understand the operation of DSCs.

We investigate the dependence of the photovoltaic performance of dye-sensitized solar cells on the cations with different charge densities, such as lithium (Li+), sodium (Na+), potassium (K+), and dimethylimidazolium (DMI+). The efficiencies of light harvesting, electron injection and charge collection were evaluated to clarify the influence of cation selection on photocurrent generation. It is found that the short-circuit photocurrents of DSCs gradually diminish with decreasing cation charge densities, partially owing to reduced electron injection rates which are intimately related to the reaction Gibbs free energies. Further experiments indicate that the upward movement of conduction band edge results in decreased reaction Gibbs free energy of electron injection from Li+ to DMI+. At an irradiation of 100 mW cm−2AM1.5 sunlight, the open-circuit photovoltage and the fill factor of a typical dye-sensitized solar cell increase in the order of Li+ < Na+ < K+ < DMI+. Analyses of impedance data reveal that the increase of cell photovoltage mainly correlates with the upward shift of the conduction band edge induced by the adsorption of low-charge-density cations on the surface of titania nanocrystals. A J–V model was proposed to understand the improvement of the fill factor. It is found that the increase of the fill factor stems from the decrease of recombination current density under the equilibrium state in the dark by fitting the J–V data with the model.