A Numerical Model for Charge Transport and Recombination in Dye-Sensitized Solar Cells

Abstract

We propose a numerical model aimed at obtaining the electrical output of dye-sensitized solar cells from microscopic parameters. The model is based on the solution of the continuity equation as a function of voltage for electron transport with both the diffusion coefficient and the recombination constant dependent on the electron density, i.e., the light intensity and/or voltage. The density dependence of the kinetic parameters can be implemented in analytical form (via a power-law expression) or extracted from experiments or electron transport simulations. We investigate the situation where the recombination rate is limited by the electron transport in the nanostructured film, as has recently been suggested by various authors. It is observed that for a power-law density dependence governed by a single alpha parameter, related to the depth and shape of a trap energy distribution, the solar cell behaves as an ideal diode, where the short-circuit current, open-circuit voltage, and current-voltage characteristics are independent of the alpha parameter. According to the formal description provided here, where recombination is limited by electron transport, lowering the trap density or changing alpha by changing the morphology or materials properties, thus improving the conductivity, would not lead to a better performance of the solar cell under steady-state conditions. The numerical results are compared to intensity-dependent current-voltage measurements on chlorophyll-sensitized TiO(2) solar cells.

Device Physics of Dye Solar Cells

“…It is generally acknowledged that under normal operating conditions most of the electrons in the TiO 2 are in fact trapped in localized states in the band gap ( Figure 13 ). However, it has been shown both theoretically [ 65 ] and by numerical simulations [ 85 ] that electron trapping does not affect the steady state operation of DSC as long as the traps do not offer an additional pathway to electron transport and recombination. Indeed, if recombination via trap states (e.g.…”

“…Transmittance of the counter electrode T CE Figure 10 [%] Optical measurements (Figure 10a) Transmittance of the bulk electrolyte layer T EL Figure 10 [%] Optical measurements (Figure 10a) Refl ectance of the photoelectrode fi lm r PE Figure 10 [%] Optical measurements (Figure 10a EIS in symmetric cell [85] Symmetry factor β 0.5 -Assumption…”

“…The apex of the arc, corresponding to a peak in the negative imaginary part vs frequency plot, is at frequency f D,i = ω D,i (2 π ) − 1 . [ 85 ] …”

Numerical model for the prediction of interfacial effect of ZnO/TCO on the performance of dye-sensitized solar cells

“…2,3 The injected electron gets transported through nanostructured film mainly due to diffusion. 4,5 The transport kinetics of flow of injected electrons is influenced by the incident intensity and trapping-detrapping mechanism. 6,7 The electric potential distribution plays a vital role in the functioning of dye-sensitized solar cells.…”

Effects of Organic Additive during Thermal Reduction of Platinum Electrodes for Dye-Sensitized Solar Cells

“…Pt electrodes are typically prepared by the thermal decomposition of Pt precursor solutions on fluorine-doped tin oxide (FTO) or indium tin oxide substrates. [9][10][11] Considering that this method can be sensitive to many factors, it is surprising to see that there have been a few reports on the control of the morphology of the Pt electrode to optimize the performance of DSSCs.…”