Soft X-Ray Spectroscopy for Solar Energy Conversion
CFM Seminars
- Speaker
-
Ioannis Zegkinoglou.Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA
- When
-
2013/12/13
12:00 - Place
- Auditorium of the Centro de Fisica de Materiales, Paseo Manuel de Lardizabal 5, Donostia-San Sebastián
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**Ioannis Zegkinoglou**
Chemical Sciences Division, Lawrence Berkeley National Laboratory
Berkeley, CA
**Soft X-Ray Spectroscopy for Solar Energy Conversion**
**Abstract**
The development of more efficient photovoltaic and photoelectrochemical
devices for solar-to-electric and solar-to-chemical energy conversion can be
accelerated by understanding and systematically tailoring the electronic
properties of their constituent materials, rather than relying exclusively on
intuition and empirical approaches. The energy positions of the band edges of
the light-harvesting substance with respect to the valence band maximum of the
electron donor and the conduction band minimum of the electron acceptor play a
key role in the efficiency of the charge generation and separation processes.
In water splitting applications additional constraints are imposed by the
oxidation and reduction potentials of the aqueous electrolyte. The optical
properties of the light absorber, the morphology of the electrode materials
and the interface properties in the boundary regions between different
materials further determine the overall energy conversion efficiency. Element-
specific, synchrotron-based, core-level soft x-ray spectroscopy techniques
were used to probe selected electron states in a manifold of both organic and
metal oxide semiconductors, as well as in combinations of them. Two example
cases will be presented in more detail: the study of custom porphyrin-based
dye molecules characterized by the highly efficient ‘donor-π-acceptor’
architecture; and the investigations on hematite-based nanostructures, aimed
to be employed as photoanodes in artificial photosynthetic applications.
Backed by optical spectroscopy as well as density functional theory (DFT) and
time-dependent density functional theory (TDDFT) calculations, we were able to
establish a feedback loop between synthesis, spectroscopy and theory, which
provided microscopic understanding of the mechanisms that determine the
efficiency of the investigated materials. The results demonstrate the great
potential of the combined use of core level spectroscopy and first principles
calculations for achieving advances in the field of solar energy conversion.