Semiconductor quantum dots (QD) have received considerable interest as a novel material in solar energy conversion devices. The attractive property of these dots is known as “quantum size effect”, where the band gap energy becomes larger by reducing QD size. By employing this concept, the light absorption wavelength range can be tuned by controlling the QD size. In addition to this effect, by selecting appropriate elements, the light absorption range can be selected from UV or visible to near infrared region. This wavelength tunability is particularly attractive to designing a photocatalytic device such as solar water splitting, hydrogen generation or CO₂ fixation devices.

The potential energy levels of the QD conduction and valence bands can also be adjusted with the QD size. An appropriate size will be selected to optimize efficient photo-induced charge separation and to retard charge recombination at the QD interfaces (Optimum Gibbs free energy difference), thereby facilitating performance improvement of solar energy conversion devices.

We are also interested in elucidating mechanisms of photocatalytic reactions at semiconductor interfaces. In particular, identification of interfacial reaction rates would be useful to design appropriate structures and selection of nanomaterials.

In this presentation, we will show some designs of synthesizing semiconductor quantum dots. Also, some examples of identifying interfacial dynamics employing time-resolved laser spectroscopies will be presented.

This work was financially supported by JST PRESTO program, Japan. The author also acknowledges Australian Research Council (ARC) LIEF grant (LE140100104) and the Office for University-Industry Collaboration, Osaka University, for the financial supports.