Experimental Studies of Ultrafast Interfacial Electron Transfer Dynamics in Semiconductor-Chromophore Assemblies based on Earth-abundant Materials
Abstract
This research program is directed toward an experimental delineation of ultrafast dynamics associated with interfacial charge-separation in chromophore-semiconductor assemblies. The specific focus is on processes subsequent to charge-transfer excitation of first-row transition metal-based chromophores attached to wide bandgap semiconductors. Such materials are of interest due to the fact that first-row metals (e.g., iron, copper, chromium, etc.) have orders of magnitude greater availability than rarer elements such as ruthenium that currently play a dominant role in this technology. Due to various issues related to the electronic properties of these "earth-abundant" elements, a fundamental understanding of structure-property correlations is essential in order for these materials to realize a transformative impact in solar energy technologies. The specific goals of the work are two-fold: (1) to establish an experimental paradigm for the study of these sorts of devices, in particular the examination of interfacial electron transfer dynamics under operational conditions, and (2) to provide data that can be used as benchmarks for the continued development and refinement of theoretical models that will first explain experimental observations, then ultimately guide new design motifs by providing insights that experiments alone cannot. To achieve this, two decadesÕ worth of experience in studying the ultrafast excited-state dynamics of transition metal-based chromophores wil be brought to bear, as well as significant expertise in the fabrication and characterization of this class of solar cells and a collaboration with a leading computational chemistry program that will ensure strong intergroup communications between the experimental and theoretical sides of this problem. The research in our group will be developed in multiple stages over the course of the proposed three-year duration of the grant. As a first step, modifications will be undertaken to existing equipment that will allow for direct probing of interfacial electron transfer dynamics of dye-sensitized solar cells. Second, the synthesis and characterization of a series of compounds is being pursued. The molecules are based on relatively straightforward metal-polypyridyl motifs but with a focus on variations in the nature of the functional groups that serve to attach the chromophore to the semiconductor substrate (known as anchoring groups or linkers). Third, a protocol that has been developed for fabricating GrŠtzel cells that yields a significant improvement in reproducibility (as gauged by cell performance metrics) will be employed: this approach will be used to fabricate and characterize solar cells employing the aforementioned chromophores as sensitizers. And finally, a series of ultrafast time-resolved optical measurements will be carried out that will provide the first comprehensive set of data on interfacial electron transfer in this class of solar cells as a function of the linker, excitation wavelength, substrate, as well as optical and potential bias. When combined with parallel theoretical efforts, an unprecedented level of understanding of these devices will emerge that we believe will allow us to identify the key parameters critical to the further development of this class of 3rd-generation solar devices.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1510487
Entities
People
- James K. McCusker
Organizations
- Army Contracting Command
- Michigan State University
- United States Army