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14 July 2008


Magnolia and Kopin to co-develop InN-based quantum dot solar cells

Magnolia Optical Technologies Inc of Woburn, MA, USA says that it is collaborating with Dr Roger Welser of Woburn-based epiwafer foundry Kopin Corp in developing indium nitride (InN)-based quantum dot solar cells for both NASA and defense applications. Magnolia and Kopin have also collaborated previously on programs using gallium nitride (GaN)-based materials.

In May, Kopin was award a $600,000 Phase II Small Business Technology Transfer (STTR) program contract from NASA. Project partners include groups at Magnolia and Virginia Polytechic Institute and State University (Virginia Tech). Phase I work had demonstrated device-quality InN-based quantum dots exhibiting strong room-temperature photoluminescence, with peak emission energies ranging from the infrared to the ultraviolet. During Phase II, the quantum dots will be embedded within a higher-bandgap GaN barrier material.

“The goal of the current [Phase II] program is to develop high-performance solar cells that are resistant to extreme conditions while achieving high solar electric power conversion efficiency,” says Welser, Kopin’s director of new business and product development. “The advanced solar cell structure incorporating InN-based nanostructures can harness a very large fraction of the solar spectrum while minimizing the effects of high temperatures and high-energy radiation,” he adds. “This technology will enable photovoltaic power systems of future NASA space exploration missions and can be applied to other defense applications.”

Magnolia says that the conversion efficiency of traditional solar cells is limited by a fundamental tradeoff between the current generated by photon absorption and the operating voltage of the device. Photons with energies less than the bandgap energy of the semiconductor pass through the device and do not contribute to the photo-generated current. High-energy photons can be absorbed, but the resulting electrons are collected and extracted at a lower voltage, limited by the bandgap.

“Quantum effects in nanostructured materials enable new innovative device concepts that can radically enhance the operation of traditional semiconductor devices,” says Magnolia’s president and CEO Dr Ashok Sood. Quantum-dot nanostructures allow the spectral response and operating voltage of a solar cell to be tailored in ways that are not possible with bulk semiconductor materials. “For example, a larger fraction of the solar spectrum can be harnessed while maximizing the solar cell operating voltage by using quantum wells and quantum dots embedded in a higher-bandgap barrier material. Nanostructured devices thus provide a means to decouple the usual dependence of short-circuit current on open-circuit voltage that limits conventional solar cell design,” Sood adds. Also, the wide range of energies accessible to InN-based materials provides unique flexibility in designing the quantum-dot solar cell structures. “Ultra-high conversion efficiencies are predicted for solar cells that collect both low- and high-energy photons from the solar spectrum while maintaining high-voltage operation,” he concludes.

“This STTR project is part of Kopin's long-term goal to address the emerging terrestrial renewable energy market by realizing the ultimate objective of high conversion efficiency at low costs,” says Kopin’s president and CEO Dr John C.C. Fan. “Ultimately our approaches can provide pathways for realizing solar cells with power conversion efficiency approaching 60%, well beyond the current state-of-the-art efficiency of 40%,” he reckons.

See related items:

Kopin grows 61% year-on-year

Kopin awarded phase II NASA STTR solar cell development contract

Search: Kopin InN Quantum dot solar cells