Opto-electronics and Light Harvesting
Description of Activities:
The conversion of light into free electron–hole pairs constitutes the key process in the fields of photodetection and photovoltaics. The efficiency of this process depends on the competition of different relaxation pathways and can be greatly enhanced when photoexcited carriers do not lose energy as heat, but instead transfer their excess energy into the production of additional electron–hole pairs through carrier–carrier scattering processes. We have used optical pump–terahertz probe measurements to show that in graphene carrier–carrier scattering is unprecedentedly efficient and dominates the ultrafast energy relaxation of photoexcited carriers, prevailing over optical-phonon emission in a wide range of photon wavelengths. Our results indicate that this leads to the production of secondary hot electrons, originating from the conduction band. As hot electrons in graphene can drive currents, multiple hot-carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.
We build on these results by studying the effects of hot carrier multipolication on the optoelectronic response and light-harvesting. We aim for the development of highly efficient photodetectors and take the first steps towards power generation by using graphene as an active material.