D) Perovskites

Within the past five years, perovskites have advanced from a nearly unknown material to one of the most promising semiconductors for thin film photovoltaics. Power conversion efficiencies of about 20% currently stimulate world wide research efforts in designing new, even more efficient cells.

Fig 8: Idealized structure of an organometal perovskite lattice and SEM image of a thin film fabricate in our group.

Our approach to pervoskites targets on the understanding of the properties of charge transport. Essential properties of perovskites, such as charge carrier masses, scattering times, and mobilities are still unknown and it appears unrealistic that without such knowledge a coordinated approach to more efficient devices will be possible. The objective of our research is the measurement of these fundamental transport properties by THz electromodulation spectroscopy. The success of our recent works on other thin film materials support this approach. First films of perovskites have been fabricated in our group and future experiments will be similar to those described in section B). Additionally, we currently set up a system for measuring the photoluminscence emitted from perovskites with a time resolution of less than 100 fs. We expect that the luminescence dynamics show the carrier transport on the scale of the individual grains of the perovskites, which typically have submicron diameter. Altogether, the THz experiments and the luminescence studies will provide access to the most important transport mechanisms. They will cover transport phenomena from the nanoscale up to the scale of the individual grains.