Quantitative study of electron transport in nanostructured materials by means of transient absorption spectroscopy

Abstract

In order to elucidate electron migration in dye-sensitised nanoporous anatase TiO 2, time-of-flight short-circuit photocurrents and transient absorption spectra between 500 and 2000 nm have been recorded. It is found that electrons in TiO 2 dominate the transient absorption between 900 and 1100 nm, whereas at wavelengths longer than 1100 nm absorption by electrons in the SnO 2/F substrate prevails. Combining transient absorption and photocurrent response data, the time-resolved recombination loss can be determined. When the excitation density is below 33.5 μJ/cm 2, on average less than one electron per nanoparticle is injected. Under this condition the IPCE equals unity. When higher excitation densities are applied, i.e. when more than one electron per nanoparticle is injected, losses become significant and the IPCE reduces to 40%. The time evolution of the recombination loss reveals that recombination primarily takes place within 20 μs.