Four pulses of laser light on nanoparticle photocells in a University of Oregon spectroscopy experiment has opened a window on how captured sunlight can be converted into electricity.
The work, which potentially could inspire devices with improved efficiency in solar energy conversion, was performed on photocells that used lead-sulfide quantum dots as photoactive semiconductor material.
In the process studied, each single photon, or particle of sunlight, that is absorbed potentially creates multiple packets of energy called excitons. These packets can subsequently generate multiple free electrons that generate electricity in a process known as multiple exciton generation (MEG). In most solar cells, each absorbed photon creates just one potential free electron.
"Spectroscopy is all about light and molecules and what they do together."Andrew H. Marcus, professor of physical chemistry and head of the UO Department of Chemistry and Biochemistry.
Multiple exciton generation is of interest because it can lead to solar cells that generate more electrical current and make them more efficient. The UO work shines new light on the little understood process of MEG in nanomaterials.
While the potential importance of MEG in solar energy conversion is under debate by scientists, the UO spectroscopy experiment should be useful for studying many other processes in photovoltaic nanomaterials, said Andrew H. Marcus, professor of physical chemistry and head of the UO Department of Chemistry and Biochemistry.
Spectroscopic experiments previously designed by Marcus to perform two-dimensional fluorescence spectroscopy of biological molecules were adapted to also measure photocurrent. "Spectroscopy is all about light and molecules and what they do together," Marcus said. "It is a really great probe that helps to tell us about the reaction pathway that connects the beginning of a chemical or physical process to its end.
"The approach is similar to looking at how molecules come together in DNA, but instead we looked at interactions within semiconductor materials," said Marcus, an affiliate in UO's Institute of Molecular Biology, Materials Science Institute and Oregon Center for Optics. "Our method made it possible to look at electronic pathways involved in creating multiple excitons. The existence of this phenomenon had only been inferred through indirect evidence. We believe we have seen the initial steps that lead to MEG-mediated photo conductivity."
The controlled sequencing of laser pulses allowed the seven-member research team to see — in femtoseconds (a femtosecond is one millionth of one billionth of a second) — the arrival of light, its interaction with resting electrons and the subsequent conversion into multiple excitons. The combined use of photocurrent and fluorescence two-dimensional spectroscopy, Marcus said, provided complementary information about the reaction pathway.
This story is reprinted from material from Oregon University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.