Semiconductor quantum dots (QD) have recently been recognized as an alternative sensitizer for dye sensitized solar cells. Intensive studies have focused on combining a different type of metal oxide nanoporous substrate; in this scenario the QDs absorb a wide range of visible and near IR wavelengths. We have reported that QDs/TiO₂ systems can generate efficient sandwich type photovoltaic devices by employing an appropriate electrolyte,^1,2 although the efficiency remains low in comparison to ruthenium dye sensitized solar cells.

Solar cell performance improvement can be achieved by controlling the interfacial kinetics, (i) accelerating charge separation rates which lead to a high quantum yield and (ii) retarding charge recombination processes. However, elucidation of the kinetic factors, i.e. electron transfer mechanisms, has rarely been studied despite the obvious impact and significance these investigations would generate. Material composition modification at the interface is an important additional factor in controlling the electron transfer reactions. For example, by introducing barrier layers at the interfaces, one can readily modulate the electron transfer kinetics,³ as shown in Fig. 1.

We will present the kinetic mechanism participating in QDs sensitized solar cells by employing various techniques including transient absorption spectroscopy and dynamic electrochemistry. Additionally introducing a barrier layer at the conducting glass/electrolyte interface and the corresponding influence on the device performance will be considered.

1. Tachibana et al., Chem. Lett., 36(1) 88-89 (2007).
2. Tachibana et al., Proc. SPIE, 6340, 634014/1-634014/13 (2006).
3. Tachibana et al., submitted.