One of the most active areas of research today is the discovery and understanding of next-generation solar cell materials. Quantum dots, perovskites, conducting polymers and many other materials are being studied in order to understand and harness their energy transfer properties. A promising new class of materials is semi-conducting carbon nanotubes where the nanotubes are used in the photoabsorbing layer, similar to molecular dyes in dye-sensitized solar cells. Isolated carbon nanotubes have extremely large exciton diffusion lengths, large carrier mobilities, low trap densities, high optical cross sections, and excellent air stability (compared to organic photovoltaic dyes) which are all critical properties for solar cells. These purified thin films represent an entirely new class of materials, whose properties need to be understood. Their ultrafast dynamics are especially important because fast exciton transfer is directly linked to solar cell performance. Using transient absorption spectroscopy, we are able to measure the time scale for energy transfer within these solar cell materials. By studying the anistropy of our transient signals, we can also gain insights into how the energy transfer is distributed spatially.
We have used our 2D WL spectroscopy to study carbon nanotubes and have found differences in the exciton coupling of solution and thin films samples. We have recently coupled our 2D WL Spectroscopy to an atomic force microscopy to bring spacial resoltuion to our non-linear spectra. With this microscopy developed in our lab, we have been exploring singlet-fision in organic thin films, specifically TIPS-pentacene, and have been able to identify how defects in a crystal influence the ultrafast dynamics of energy transfer.
The Zanni group has also begun to explore the energy transfer in perovskites. We make our own lead halide perovskites with different organic cations to determine how the composition of the material influences the energy transfer properties.
- Selected Publications
- Mehlenbacher, R. D.; Wu, M.-Y.; Grechko, M.; Laaser, J. E.; Arnold, M. S.; Zanni, M. T. Photoexcitation Dynamics of Coupled Semiconducting Carbon Nanotube Thin Films. Nano Lett. 2013, 13, 1495–1501.
- Grechko, M.; Ye, Y.; Mehlenbacher, R. D.; McDonough, T. J.; Wu, M.-Y.; Jacobberger, R. M.; Arnold, M. S.; Zanni, M. T. Diffusion-Assisted Photoexcitation Transfer in Coupled Semiconducting Carbon Nanotube Thin Films. ACS Nano 2014, 8, 5383–5394.