Invited Paper SA-MoA6
Synchrotron-Based Spectroscopy Shedding Light on Solar Cells

Monday, November 10, 2014, 3:40 pm, Room 312

After briefly discussing the role of photovoltaics in the current energy picture, this talk illustrates how spectroscopy with soft X-rays can assist the development of new types of solar cells with improved price/performance ratio. The starting point is the most general layout of a solar cell, which involves of a light absorber sandwiched between an electron donor and an electron acceptor. In contrast to the widely-used silicon solar cells, one can choose three different materials to optimize the four energy levels that are crucial for the performance of a solar cell. These are measured by a combination of X-ray absorption spectroscopy and photoelectron spectroscopy. Close coupling with first principles calculations makes it possible to discover and exploit systematic trends. Examples will be given, such as the combination of all three components in one molecule (donor-π-acceptor complexes [1],[2]). In addition to the energy levels one has to consider the lifetime of the photo-generated carriers. A future dream experiment will be discussed where the carriers are followed in real time on their way from the absorber to the contact electrodes, using pump-probe techniques at the latest generation of soft X-ray light sources. Such experiments have been performed in the UV/visible [3], but they would greatly benefit from the element- and bond-specific capabilities of X-ray absorption spectroscopy.

[1] A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, Md. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin, M. Grätzel, Science 334, 629 (2011).

[2] I. Zegkinoglou, M.-E. Ragoussi, C. D. Pemmaraju, P. S. Johnson, D. F. Pickup, J. E. Ortega, D. Prendergast, G. de la Torre, and F. J. Himpsel, J. Phys. Chem. C 117, 13357 (2013).