Microwave Transient Photoconductivity Studies in Porous Semiconductors

Porteanu, Horia‐Eugen; Konstantinova, Elisaveta; Кытин, В. Г.; Loginenko, O.; Timoshenko, V. Yu.; Dittrich, Thomas; Koch, F.; München, T.U.

doi:10.1557/proc-699-r4.8

Cited by 1 publication

(1 citation statement)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, time-resolved microwave studies of nanocrystalline titania (TiO 2 ) show that photoexcitation can also lead to large changes in the real component of the complex permittivity. , For example, Kytin et al have reported UV-induced changes in the real component of the microwave permittivity of 6 and 16 nm anatase particles that are comparable in magnitude to the changes in the imaginary component. Trapped electrons may also contribute to the light-induced microwave reflectance response of compound semiconductors or materials such as nanocrystalline films , and polymers …”

Section: Introductionmentioning

confidence: 99%

In Situ Detection of Free and Trapped Electrons in Dye-Sensitized Solar Cells by Photo-Induced Microwave Reflectance Measurements

et al. 2012

View full text Add to dashboard Cite

In order to study the behavior of photoinjected electrons in dye-sensitized solar cells (DSC), steady-state microwave reflectance measurements (33 GHz, Ka band) have been carried out on a working cell filled with electrolyte. The experimental arrangement allowed simultaneous measurement of the light-induced changes in microwave reflectance and open circuit voltage as a function of illumination intensity. In addition, frequency-resolved intensity-modulated microwave reflectance measurements were used to characterize the relaxation of the electron concentration at open circuit by interfacial transfer to tri-iodide ions in the electrolyte. The dependence of the free and trapped electron concentrations on open circuit voltage were derived, respectively, from conductivity data (obtained by impedance spectroscopy) and from light-induced near IR transmittance changes. These electron concentrations were used in the fitting of the microwave reflectivity response, with electron mobility as the main variable. Changes in the complex permittivity of the mesoporous films were calculated using Drude–Zener theory for free electrons and a simple harmonic oscillator model for trapped electrons. Comparison of the calculated microwave reflectance changes with the experimental data showed that the experimental response arises primarily from the perturbation of the real component of the complex permittivity by the high concentration of trapped electrons present in the DSC under illumination. The results suggest that caution is needed when interpreting the results of microwave reflectance measurements on materials with high concentrations of electron (or hole) traps, since an a priori assumption that the microwave response is solely determined by changes in conductivity (i.e., by free electrons) may be incorrect. The intensity-modulated microwave reflectance measurements showed that relaxation of the free and trapped electron concentrations occurs on a similar time scale, confirming that the free and trapped electron populations remain in quasi-equilibrium during the decay of the electron concentration.

show abstract