PHaSE research on polymer-based solar materials is not about replacing silicon as a semi-conductor, but rather developing readily processed, more flexible, and less expensive polymer materials for new solar energy applications.
Funded by the Department of Energy, PHaSE research focuses on organic photovoltaic (OPV) cell improvement, using polymers, organic compounds, and special composites of organic/inorganic compounds. PHaSE researchers work with the common goal of maximizing photoconversion efficiency—how much light is absorbed versus how much electricity is emitted. Since the center’s inception in 2008, the PHaSE team has been able to double the photoconversion efficiency of polymer-based solar materials under their design.
Co-directed by Thomas Russell (Polymer Science and Engineering) and Paul Lahti (Chemistry), the center focuses on three major areas of research: polymer-based architecture—design and synthesis; controlled assemblies and morphologies; and photophysical characterization, device design and integration. Chemists, chemical engineers, polymer scientists, and physicists comprise the interdisciplinary research team of faculty, post doctoral associates, and graduate students.
“We’ve actually broken the barrier to bring these materials to be commercially viable,” says Russell.
Russell is a leading expert in materials research and an international leader in the interfacial properties of polymers and the structural morphology of polymer-based photovoltaic materials. Lahti is an expert in theoretical, synthetic, and physical chemistry and the electronic properties of molecules, polymers, and materials.
Russell and Lahti explain that PHaSE research with polymer-based solar materials is not about replacing silicon as a semi-conductor, but rather developing readily processed, more flexible, and less expensive polymer materials for new solar energy applications.
“People have been working on silicon for a long time…a lot of engineering has gone into it. The work we’re doing is about choices—developing the science behind the technology to give people new choices in the market place,” says Lahti.
The polymers Russell, Lahti, and their colleagues work on are highly tunable. Because PHaSE researchers are creating new polymers, they can design them to absorb light in specific ways and at points in the spectrum where there is the most energy available. Their physical flexibility is also a key asset. Imagine a small, bendable pad made of conductive polymer that can be placed on a car windshield to power a phone or GPS device, or a conductive polymer coating embedded in the fabric of a backpack to power portable devices during camping trips. Polymeric materials might not yield as much electricity as silicon, but they can be used in many more places and ways—silicon is not bendable and is not readily portable. Processing also gives a huge edge for polymeric based materials. Once a polymeric semi-conductor is perfected, it can be put into devices in a highly reproducible way at little energy and cost.
To test and validate polymers, Russell, Lahti, and colleagues use a method called spin-casting to deposit polymer strips onto glass slides which have been pre-treated with layers of thin, conductive materials. A liquid solution of the polymer is dropped onto a spinning disk, from which most of the liquid wicks away, leaving a thin coating. The researchers then measure their photoconversion efficiencies. Once the polymer materials are fine-tuned in this fashion, Russell and Lahti plan to utilize the Roll-to-Roll Nanofabrication Laboratory (based in the campus’s Center for Hierarchical Manufacturing) to print them onto larger surfaces. This method of production enables researchers to embed nano-sized polymers into an array of materials by means of printing. With this capability, the potential applications are vast—imagine a polymer-coated car-cover that helps power your car's instruments.
In another project with implications for polymer assembly in photovoltaic technologies, Russell, polymer scientist Todd Emrick, and graduate student Mengmeng Cui recently made a big splash in the field of materials science by discovering how to kinetically trap and control one liquid within another. By generating jammed nanoparticle surfactants at interfaces, fluid drops of any shape or size can be stabilized, opening applications in fluidics, encapsulation and bicontinuous media for energy applications. This discovery will help the team better encapsulate organic polymers within the solar materials, and by stretching the lifespan of the organic polymers, make for a more robust technology.
Funded through the Department of Energy’s Office of Basic Energy Sciences, the fundamental discoveries and scientific innovations made by PHaSE researchers are being shared with government agencies, laboratories, and industry leaders around the world including in Germany, Japan, Korea, China, and India.
The broader impacts of PHaSE research to date include more than 100 scientific research publications that have changed basic approaches toward optimizing solar energy conversion in organic polymer materials; the creation of a state-of-the-art facility for evaluating new test materials; and strong collaborative ties to national laboratories (Oak Ridge, Lawrence Berkley Lab, and Brookhaven) as well as numerous academic partners. And PhaSE’s most important product may be the well-trained Ph.D.’s and post-doctoral level scientists who are prepared for the fast paced scientific marketplace of materials energy research.
Lahti explains that expertise is so well distributed throughout the center that it is not uncommon for many people from multiple groups to be contributing to one project.
“We’ve become so team oriented…a lot of projects might have a birthplace with a particular person but evolve to many because no single research group has all the expertise and all the pieces,” says Lahti.
“The biggest discoveries are often made serendipitously,” Russell notes. “You have to be curious, you have to want to explore, to go to places people haven’t been.”
Amanda Drane ‘12