Section: New Results

Computational materials spectroscopy in electrochemistry and optoelectronics

Participant : Ismaila Dabo.

Many advances in the understanding and design of nanomaterials have been enabled by spectroscopic techniques of increasing spatial and temporal resolution. In electrochemistry and optoelectronics, spectroscopy provides insight into the chain of processes involved in harnessing, storing, and delivering energy.

In support to experimental techniques, much progress has been achieved in simulating spectroscopic phenomena to shed light into energy conversion at the molecular scale. Such understanding is critical to the molecular design of a range of electrical devices, including but not limited to fuel cells, batteries, dye-sensitized solar cells, and optoelectronic devices.

The work of I. Dabo is dedicated to the development of quantum and semiclassical methods to simulate spectroscopies of electrochemical and optoelectronic materials. The achieved level of efficiency and accuracy fosters dialogue between experiment and theory for interpreting complex spectroscopic data. This year, these novel methods have been applied to simulate spectroscopic phenomena spanning the infrared to the visible and ultraviolet ranges.

The first application pertains to the infrared sum-frequency-generation (SFG) spectroscopy of adsorption mechanisms at the origin of the tolerance of fuel-cell catalytic electrodes to chemical poisoning. The study explains the critical influence of the electrode voltage in analyzing surface spectroscopy experiments (work done in collaboration with EPFL). [12] , [26] , [19]

The second application aims at understanding the sensitizing properties of organometallic dyes in dye-sensitized solar cells by simulating optical photoluminescence (PL) spectra, thereby elucidating the role of electron localization and ligand functionalization on the phosphorescence of organometallic complexes (work done in collaboration with the University of Minnesota). [33]

The third application is focused on the ultraviolet photoelectron spectroscopy (UPS) of photoactive nanomaterials of relevance to the design of organic photovoltaic junctions and photoelectrodes (work done in collaboration with the Italian Institute of Nanoscience, Seoul National University, and Xiamen University). [27]

Future challenges and opportunities are related to the time-dependent simulation of transient and cyclic spectra. These developments, which will be part of the widely used Quantum-ESPRESSO distribution (http://www.quantum-espresso.org ), would pave the way for comprehensive studies of kinetic processes in tandem with time-resolved spectroscopic experiments.