Time resolved photoelectrochemistry with size-quantized PbS adsorbed on gold

The electronic structure and decay dynamics of a long-lived photoexcited state in PbS quantum dots (QD), adsorbed as a monolayer on a gold electrode, were studied by a time resolved photoelectrochemical technique, intensity-modulated photocurrent spectroscopy (IMPS). By scanning the Fermi level of the gold, we found that the excited state consists of an electron in a deep trap and a hole in the HOMO. The rate constants of photoinduced electron tunneling between the dots and the electrode and between the dots and the electrolyte were determined. It was found that the trapped charge carrier has a lower tunneling probability than the free charge carrier, indicating that distance is the determining parameter for electron tunneling.