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Welser R.E.,Magnolia Solar, Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

While radiative recombination is a well-known intrinsic loss mechanism in photovoltaic devices, nonradiative recombination mechanisms typically dominate compound semiconductor diode currents and limit the performance of even state-of-the-art devices. However, recent advances in device structure design have allowed quantum well structures to begin reaching the radiative limits of dark current operation. In this work, a novel extended heterojunction structure is employed in InGaAs quantum well devices to reduce non-radiative recombination and expose the limiting n=1 radiative component of the diode current. Short circuit current versus open circuit voltage curves derived from illuminated currentvoltage measurements indicate that the underlying dark diode currents of the InGaAs quantum well devices vary with well thickness and emission energy. Analysis of the extracted n=1 saturation current densities indicate that these high-voltage InGaAs quantum well devices are operating in a regime of suppressed radiative recombination. © 2012 SPIE. Source

Welser R.E.,Magnolia Optical Technologies,Inc. | Welser R.E.,Magnolia Solar, Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Nano-enhanced solar cells incorporating III-V quantum wells or quantum dots have the potential to revolutionize the performance of photovoltaic devices. Extended spectral response characteristics have been widely demonstrated in both quantum well and quantum dot solar cells using a variety of different III-V materials. To fully leverage the increased spectral response of nano-enhanced solar cells, new device designs are discussed that can both maximize the current generating capability of the limited volume of narrow band-gap material and minimize the unwanted carrier recombination that degrades the voltage output. © 2013 Copyright SPIE. Source

Ultra-high reflectivity is projected for internal reflectors comprised of a metal film and nanostructured transparent conductive oxide (TCO) bi-layer on the back side of a semiconductor device. Oblique-angle deposition can be used to fabricate indium tin oxide (ITO) and other TCO optical thin-film coatings with a porous, columnar nanostructure. The resulting low-n dielectric films can then be employed as part of a conductive omni-directional reflector (ODR) structure capable of achieving high internal reflectivity over a broad spectrum of wavelengths and a wide range of angles. In addition, the dimensions and geometry of the nanostructured, low-n TCO films can be adjusted to enable diffuse reflections via Mie scattering. Diffuse ODR structures enhance the performance of light trapping and light guiding structures in photonic devices.

Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 100.00K | Year: 2010

Magnolia Solar proposes to develop an innovative high efficiency single junction solar cell working with Prof. Diana Huffaker and her group and utilizing multi photon absorption in InAsSb/AlAsSb quantum dot solar cells. The proposed structure has unique qualities required by Intermediate band solar cell theory to achieve ultra high conversion efficiency. This system has a potential to achieve efficiencies over 50% under concentrated light conditions. The proposed structure has optimum band alignment as well as bandgap for Quantum dot and barrier materials. InAsSb QDs in AlAsSb barriers forms a type II band alignment which has long carrier life times and hence high carrier extraction efficiencies are possible. During the Phase I STTR effort, we will synthesize InAsSb dots with excellent structural and optical properties and demonstrate the technical feasibility of InAsSb Quantum Dot solar cells. Device simulation and modeling will help supplement the device optimization work. Our broad experience in band engineering, simulation and device design will help obtain optimum material properties needed for demonstrating multi-photon solar cells. BENEFIT: The terrestrial, Defense and Spacecraft power photovoltaic markets provide a significant commercial opportunity for the technology developed during this SBIR effort. The worldwide PV market generates over $4.5 billion (US) per year in revenue and has been growing at over 30% annually since the late 1990s. The emphasis on renewal energy and more of the defense energy needs will grow over the next decade and is expected to grow to over 100 Billion in the next ten years. Continued growth in the commercial PV market is currently being hampered by market down turn, while space-based PV systems will utilize technologies that improve radiation hardness, operating temperature range, efficiency, and specific power. Our technology development and commercialization strategy involves several distinct steps. Magnolia has detailed the tremendous long term benefits of increasing the efficiency of Solar cells for terrestrial applications. In addition use of the micro-concentrators also provides a means of inserting Quantum Dot-based solar cells with innovative nanostructured coatings into the renewable energy market.

Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2011

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.

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