Highlight
Nanostructured materials for next-generation solar cells
Molecular structure of new material
Achievement/Results
Working with a team of interdisciplinary engineers and scientists at Cornell University, NSF-funded IGERT Fellows Brian Koo (Materials for a Sustainable Future IGERT) and Jennifer Novotney (Nanoscale Surfaces and Interfaces IGERT) have developed ordered organic thin films with vertical, atomically-precise, nanometer-scale pores. This architecture is thought to be ideal for the construction of organic (“plastic”) solar cells that would be much less expensive than today’s silicon-based devices. Although organic solar cells have been built in the lab, designs based on conventional organic materials are too inefficient for widespread application.
The new material is formed from two inexpensive building blocks (small molecules) that spontaneously assemble into a highly porous crystal or “covalent organic framework (COF)” upon mixing. Although more than 30 COFs have been synthesized to date, the new material has significantly larger pores than previous COFs. In proposed solar cell designs, a second material will be used to fill the large pores, creating a highly interdigitated structure ideal for turning light into electricity. The team also hopes to use these large-pore COFs for organizing other nanostructures, such as inorganic nanoparticles, over large areas.
One of the biggest challenges in this research was in understanding the structure of the tiny pores. The new material is a actually stack of huge single-molecule-thick sheets. But are the sheets stacked exactly on top of one another to form perfect vertical pores or are they slightly offset, forming tilted pores? The Cornell team answered this question using a combination of theoretical calculations, performed by chemical engineer Brian Koo and others, and experimental measurements, performed by chemist Jennifer Novotney and others. They showed that the stacking is not perfect. Instead each sheet is offset by ~4% of a pore diameter from its neighbors. This tight integration of theory and experiment will be crucial for the design of new materials with even better performance.
Address Goals
Discovery: The development of sustainable materials for high-efficiency solar cells is a technological and economic imperative. By 2050, current estimates suggest a doubling of today’s energy demand. To keep atmospheric CO2 below 650 ppm (present 380 ppm) — where current projections place it in 2050 — significant changes in energy technologies will be required. The primary challenge in solar-electric conversion is to lower the materials cost per watt of solar energy, as conventional photovoltaics (PVs) are intrinsically expensive due to the high cost of crystalline silicon.
Learning: This Integrative Graduate Education and Research Traineeship (IGERT) program is providing the next generation of scientists and engineers with the knowledge and skills necessary to solve the biggest problem challenging mankind: ensuring a sustainable future. This advance involved two IGERT Fellows — one specializing in synthetic chemistry and the other in computational chemical engineering — in a team-based, interdisciplinary project that required distinct, sustained contributions from researchers of different expertise and background. A recent National Academies report concluded that in-depth research experience is the crucial component in graduate education. A team-based approach provided the necessary broad skillset while also providing the Fellows an introduction to team-based Ramp;&D. A second National Academies report found that the ability to work well in teams was essentially ignored in current graduate education even though this skill is crucial to professional success.
