The Electrochemical Impedance of One-Equivalent Electrode Processes at Dark Semiconductor|Redox Electrodes Involving Charge Transfer through Surface States. 1. Theory

Abstract

Electrode processes at redox electrodes consist of mass transport to and from the electrode|electrolyte interface and of charge transfer across this interface. At n-type semiconductor electrodes, charge transfer may involve either direct exchange of conduction band electrons or direct exchange of valence band holes, accompanied by an electron-hole recombination step, or surface-state mediated transfer of conduction band electrons. In this paper, the electrochemical impedance of the dark n-type semiconductor|redox electrode is derived, taking into account both mass transport and charge transfer through surface states. The impedance expression obtained leads to a novel equivalent circuit. More limited calculations, previously published in the literature, are comprised in the treatment as special cases. Finally, it is shown how the impedance expression obtained may be also used to describe reactions involving direct exchange of majority charge carriers or direct injection of minority charge carriers followed by a recombination step.

Theory of the impedance of charge transfer via surface states in dye-sensitized solar cells

“…Eq. (12) in combination with the trap dynamics in (3) form the basis for the subsequent model calculations in this paper.…”

“…(35) implies that the impedance of the model of Eq. (12) consists of three parallel contributions, as indicated in Fig. 2a.…”

“…In the literature of photoelectrochemistry there are detailed treatment of the dynamic effects of surface states [4,[9][10][11][12][13][14][15]. We have presented calculations of the effect of surface states in DSC in steady state [16][17][18], and we have also characterized quite generally the dynamics of traps in terms of Impedance Spectroscopy (IS) [19,20].…”

“…1 of a mesoporous semiconductor that contains a transport state that can be controlled by the potential applied in the substrate, and a localized surface state. To simplify the treatment, and focus on the required features, diffusion in the transport state is assumed infinitely fast, and band unpinning (a property often considered in photoelectrochemistry [12,15]) is neglected as well. These features are briefly commented in the final section of the paper.…”

Carrier density and interfacial kinetics of mesoporous TiO2 in aqueous electrolyte determined by impedance spectroscopy

“…Previous investigations of electrochemical impedance spectroscopy (EIS) employed to elucidate molecular mechanisms at the TiO 2 /solution interface highlighted the key role of surface states on the electrode kinetics [16][17][18][19]. The present study is aimed at obtaining information about carrier dynamics in mesoporous TiO 2 by monitoring the electron dynamics, particularly the electron conductivity, recombination resistance and chemical capacitance from impedance spectroscopy measurements.…”