Solar cells are increasingly common in many parts of the world, both on rooftops and in large scale solar power stations. Solar cells provide cost-effective power without wires and so are useful for "off-grid" applications. For example, solar cells power sensor networks and provide portable power. They are also the primary power source for satellites, as well as space vehicles used for planetary exploration. Traditional solar cells lose efficiency as temperature increases. Consequently, any place where temperatures exceed 300 degrees Fahrenheit has traditionally been considered off-limits. As a result, innovative power generation schemes that could benefit from the ability to use both heat energy and solar energy at the same time have never been realized. In comparison to Mars, which has been extensively explored by solar-powered robotic vehicles, we know surprisingly little about our very hot nearby neighbors of Venus and Mercury. Solar-powered vehicles could change this. This project aims to advance the burgeoning field of high-temperature solar cells by demonstrating durable new designs that can achieve high efficiency at temperatures above 800 degrees Fahrenheit. Solar cells based on nitrides of Group III elements such as gallium and indium have shown an unusual increase in efficiency with rising temperature. This opens up the possibility of efficient solar cells that operate at high temperature. Beyond the applications above, this project could also lead to sensors that operate efficiently and wirelessly in demanding environments, such as engines. The two co-PIs will seek to incorporate solar cell testing into teacher training programs at their respective institutions. They will also incorporate research into graduate and undergraduate classes and continue their commitment to recruiting under-represented students into STEM careers.
Lee and Zhao aim to combine the unique strengths of III-V and III-N materials using wafer bonding to form multi-junction devices optimized for high temperatures of 300-450C. High-temperature solar cells are needed for inner solar system exploration and hybrid photovoltaic-thermal energy systems. III-V solar cells exhibit the highest-known efficiencies, but their performance decreases with increasing temperature. In contrast, III-N solar cells have recently demonstrated the unusual characteristic of increasing in efficiency with rising temperature. The two co-PIs will take an interdisciplinary approach to demonstrate high-efficiency photovoltaics at high temperature, combining epitaxial growth, materials characterization, device fabrication, device testing, and modeling. This project will advance understanding of optoelectronic device performance at high operating temperatures. The impact of thermal energy on phenomena such as thermionic emission and radiative recombination have widely been studied at cryogenic temperatures, with less attention paid to elevated temperatures of 300-450C. The co-PIs hypothesize that optoelectronic devices can be redesigned to account for and, in some cases, take advantage of such elevated temperatures.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
