Excited-state dynamics in CdS quantum dots adsorbed on a metal electrode

The electronic structure and decay dynamics of a long-lived excited state i n CdS quantum dots (Q-CdS) were investigated in a novel way by a time-resol ved optoelectrical method. Q-CdS was adsorbed as a monolayer on a gold elec trode and used in a photoelectrochemical cell, the gold/Q-CdS/electrolyte s tructure forming a double-barrier tunnel junction. The rates of photoinduce d tunneling processes were measured by intensity-modulated photocurrent spe ctroscopy (IMPS). These tunneling processes compete with intraparticle deca y of a long-lived excited state. In this way the excited-state dynamics cou ld be studied. From a scan of the gold Fermi level, it was deduced that the long-lived excited state consists of an electron in the LUMO and a hole tr apped in a level high in the bandgap.