Researchers are looking into radical new ways to improve solar power and give the industry more options to explore. Chemists propose making solar cells out of a naturally abundant material called molybdenum disulfide rather than silicon. The researchers conducted a series of experiments using a novel combination of photoelectrochemical and spectroscopic techniques to demonstrate that extremely thin films of molybdenum disulfide exhibit unprecedented charge carrier properties that could someday significantly improve solar technologies.
Solar power technologies, which use solar cells to convert sunlight into electricity or storable fuels, are gaining traction in a world seeking alternatives to fossil fuels for energy.
The dark bluish solar panels that dot today’s rooftops and open fields are typically made of silicon, a tried-and-true semiconductor material. However, silicon photovoltaic technology has limitations, losing up to 40% of the energy it collects from sunlight as heat waste. Colorado State University researchers are investigating radical new ways to improve solar power and provide more options for the industry to explore.
This work paves the way for knowing how to design reactors that contain these nanoscale materials for efficient and large-scale hydrogen production.
Andrés Montoya-Castillo
CSU chemists propose making solar cells out of a naturally occurring material called molybdenum disulfide, rather than silicon. The researchers conducted a series of experiments using a novel combination of photoelectrochemical and spectroscopic techniques to demonstrate that extremely thin films of molybdenum disulfide exhibit unprecedented charge carrier properties that could someday significantly improve solar technologies.
The experiments were led by chemistry Ph.D. student Rachelle Austin and postdoctoral researcher Yusef Farah. Austin works jointly in the labs of Justin Sambur, associate professor in the Department of Chemistry, and Amber Krummel, associate professor in the same department. Farah is a former Ph.D. student in Krummel’s lab. Their work is published in Proceedings of the National Academy of Sciences.
Chemists propose ultrathin material for doubling solar cell efficiency
The collaboration brought together Sambur’s expertise in solar energy conversion using nanoscale materials, and Krummel’s expertise in ultrafast laser spectroscopy, for understanding how different materials are structured and how they behave. Sambur’s lab had become interested in molybdenum sulfide as a possible alternative solar material based on preliminary data on its light absorption capabilities even when only three atoms thick, explained Austin.
They turned to Krummel, whose lab houses a cutting-edge ultrafast pump-probe transient absorption spectrometer capable of measuring the sequential energy states of individual electrons as they are excited with a laser pulse. Experiments performed with this specialized instrument can provide snapshots of how charges flow in a system. Austin built a photoelectrochemical cell out of a single atomic layer of molybdenum sulfide, and she and Farah tracked the cooling of electrons as they moved through the material using the pump-probe laser.
What they discovered was astonishingly efficient light-to-energy conversion. More importantly, the laser spectroscopy experiments enabled them to demonstrate why this efficient conversion was possible.
They discovered that the material was so good at converting light to energy because its crystal structure allows it to extract and exploit the energy of so-called hot carriers, which are highly energetic electrons that are briefly excited from their ground states when exposed to enough visible light. Austin and Farah discovered that in their photoelectrochemical cell, the energy from these hot carriers was immediately converted into photocurrent rather than being lost as heat. This hot carrier extraction phenomenon does not exist in conventional silicon solar cells.
“This work paves the way for knowing how to design reactors that contain these nanoscale materials for efficient and large-scale hydrogen production,” said Sambur.
Professor Andrés Montoya-Castillo and Dr. Thomas Sayer of the University of Colorado Boulder contributed theoretical chemistry and computational modeling to help explain and validate the experimental data.
“The discovery required a ‘team science’ approach that brought together many different types of expertise, including computational, analytical, and physical chemistry,” Krummel explained.
