Characteristics of High Efficiency Dye-Sensitized Solar Cells

TLDR

Impedance spectroscopy was used to probe high‑efficiency (11.1% and 10.2%) dye‑sensitized TiO₂ solar cells. The study interprets key impedance parameters—chemical capacitance, transport resistance, diffusion coefficient, and recombination resistance—within a unified framework based on an exponential distribution of localized states, confirming the multiple‑trapping model for electron transport, rationalizing Tafel‑type recombination via the Marcus model, and reconstructing the current‑potential curve to dissect resistive contributions to the efficiencies.

Abstract

Impedance spectroscopy was applied to investigate the characteristics of dye-sensitized nanostructured TiO2 solar cells (DSC) with high efficiencies of light to electricity conversion of 11.1% and 10.2%. The different parameters, that is, chemical capacitance, steady-state transport resistance, transient diffusion coefficient, and charge-transfer (recombination) resistance, have been interpreted in a unified and consistent framework, in which an exponential distribution of the localized states in the TiO2 band gap plays a central role. The temperature variation of the chemical diffusion coefficient dependence on the Fermi-level position has been observed consistently with the standard multiple trapping model of electron transport in disordered semiconductors. A Tafel dependence of the recombination resistance dependence on bias potential has been rationalized in terms of the charge transfer from a distribution of surface states using the Marcus model of electron transfer. The current-potential curve of the solar cells has been independently constructed from the impedance parameters, allowing a separate analysis of the contribution of different resistive processes to the overall conversion efficiency.