Description: The long-term objective of this program is to develop flexible, lightweight, single-junction solar cells using quantum structured designs that can achieve ultra-high efficiencies (approaching 45%) while avoiding the current matching issues that plague high-efficiency multi-junction devices. Ultra-low dark currents and record-high open circuit voltages have recently been achieved with a novel III-V material structure that includes both an InGaAs quantum well absorber and an extended wide band gap emitter. By enhancing absorption in the narrow band gap well, power conversion efficiencies in single-junction quantum solar cells can potentially exceed those of multi-junction photovoltaic devices. The objective of the Phase I SBIR effort is to design and prototype a high performance quantum well solar cell device incorporating advanced light trapping techniques. To enhance light trapping, we will leverage both an established epitaxial liftoff process and unique optical coatings to scatter light laterally into waveguide modes within the InGaAs well region of the device.

Benefits: The SBIR project described here is part of a larger effort to realize the ultimate objective of third generation photovoltaics, namely ultra-high conversion efficiency at low costs. Concentrator technologies can radically alter the renewable energy market in the near term like no other competing technology. By replacing expensive semiconductor materials with cheaper plastic lens and/or metal mirrors, concentrator photovoltaic (CPV) systems can in principle both reduce overall photovoltaic module costs and improve performance. The wider operating conditions enabled by quantum structured III-V solar cells could substantially enhance the overall performance of terrestrial CPV systems. CPV cells employing structures similar to the one to be developed in this project could thus accelerate the adoption of concentrator photovoltaics into the renewable energy market to address the world's growing energy needs without degrading the environment. In addition to its potential commercial value and social benefits, this SBIR program will enhance the technical understanding of quantum well and quantum dot devices.

Future space exploration missions will require lightweight photovoltaic power systems capable of operating over a wide range of conditions, ranging from extreme environments with high temperatures and tremendous radiation exposures to low temperature, low intensity conditions. Conventional multi-junction solar cells can provide high conversion efficiencies, but only under limited environmental conditions. The near term objective of this SBIR program is to build a thin, flexible solar cell, using a quantum well active region and incorporating advanced light trapping structures, that matches the conversion efficiency of conventional multi-junction technologies while performing over a much wider range of operating conditions. The primary benefit to NASA will be the creation of a solar cell technology that can operate at high efficiencies over a wide range of operating conditions, avoiding costly mission-specific redesigns of the solar cells and providing a more robust source of power for planetary exploration missions. In addition, this cell technology can be delivered in a lightweight and flexible format that can maximize the science load on exploratory spacecraft.