Direct Measurement of the Internal Electron Quasi-Fermi Level in Dye Sensitized Solar Cells Using a Titanium Secondary Electrode

Abstract

The spatial dependence of the electron quasi-Fermi level (QFL) in the interior of dye sensitized nanocrystalline solar cells (DSC) under short circuit conditions can be inferred from calculations based on a diffusive electron transport model. The calculations predict that the difference in the QFL between the electrolyte and contact sides of the TiO(2) layer under short circuit conditions at 1 sun could be as much as 0.5-0.7 eV. The predicted QFL profiles depend on assumptions made about energy positions, electron mobility, and the conduction band density of states. In this work, the position of the QFL at the electrolyte side of the dye sensitized TiO(2) film in a DSC has been measured using a thin passivated titanium contact deposited on top of the nanocrystalline TiO(2) by evaporation. The method allows changes in the electron QFL at all points on the IV characteristic of the cell to be monitored under dark and photostationary conditions. In addition, cells incorporating the titanium electrode can give information about the behavior of the QFL under dynamic conditions.

Influence of Electrolyte Cations on Electron Transport and Electron Transfer in Dye-Sensitized Solar Cells

“…The difference indicates that n E F is lower at short circuit than at open circuit. This has been confirmed in our previous work using a titanium sensor electrode and by near-IR transmittance 21,[33][34][35] and also by Boschloo et al by an interrupt technique. 36 The plot shown in Figure 5 can be used to estimate  n E F , the difference in mean n E F values at open and short circuit, which corresponds to the horizontal translation on the voltage axis that is required to bring the two plots into coincidence.…”

Interpretation of Optoelectronic Transient and Charge Extraction Measurements in Dye‐Sensitized Solar Cells

“…An alternative method to determine the internal voltage with a device was developed by Lobato et al who deposited a titanium secondary electrode on the EE surface of the TiO‐ 2 film within the device 142. This approach was also used to demonstrate the internal potential at short circuit with DSSCs 29…”

Physical electrochemistry of nanostructured devices

“…As mentioned before it is well established that nanostructured TiO 2 used in DSC (anatase) shows this type of distribution of states in the bandgap, 13,40,66,82,95 and even the direct monitoring of Fermi level has been realized. 194,195 The main features of the MT model for this distribution 55 are illustrated in simulation in Fig. 21 with realistic parameter values.…”