news review
NRL unveils III-V solar cell for beating the 50% barrier
US NAVAL RESEARCH LABORATORY scientists in the Electronics Technology and Science Division, in collaboration with the Imperial College London and MicroLink Devices, Inc., Niles, IL, have proposed a novel triple-junction solar cell.
They say the cell has the potential to break the 50 percent conversion efficiency barrier, which is the current goal in multi- junction photovoltaic development.
“This research has produced a novel, realistically achievable, lattice-matched, multi-junction solar cell design with the potential to break the 50 percent power conversion efficiency mark under concentrated illumination,” says NRL research physicist Robert Walters.
“At present, the world record triple-junction solar cell efficiency is 44 percent under concentration and it is generally accepted that a major technology breakthrough will be required for the efficiency of these cells to increase much further.”
In multi-junction solar cells, each junction is ‘tuned’ to different wavelength bands in the solar spectrum to increase efficiency. High bandgap semiconductor material is used to absorb the short wavelength radiation with longer wavelength parts transmitted to subsequent semiconductors.
In theory, an infinite-junction cell could obtain a maximum power conversion percentage of nearly 87 percent. The challenge is to develop a semiconductor material system that can attain a wide range of bandgaps and be grown with high crystalline quality.
By exploring novel semiconductor materials and applying band structure engineering, via strain-balanced quantum wells, the NRL research team has produced a design for a MJ solar cell that can achieve direct band gaps from 0.7 to 1.8 electron volts (eV) with materials that are all lattice-matched to an InP substrate.
“Having all lattice-matched materials with this wide range of band gaps is the key to breaking the current world record,” adds
Focus Lightings to double LED production with Aixtron reactors
CHINA’S Focus Lightings Tech Inc. has ordered a number of Aixtron CRIUS II-L systems for mass production of GaN LED epitaxial wafers. The systems will be configured to handle up to 69 x 2-inch wafers per run.
Schematic diagram of a multi-junction solar cell formed from materials lattice- matched to InP and achieving the bandgaps for maximum efficiency
Walters. “It is well known that materials lattice-matched to InP can achieve band gaps of about 1.4 eV and below, but no ternary alloy semiconductors exist with a higher direct band-gap.”
The primary innovation enabling this new path to high efficiency is the identification of InAlAsSb quaternary alloys as a high band gap material layer that can be grown lattice-matched to InP.
Drawing from their experience with Sb-based compounds for detector and laser applications, NRL scientists modelled the band structure of InAlAsSb and showed that this material could potentially achieve a direct band-gap as high as 1.8eV.
With this result, and using a model that includes both radiative and non-radiative recombination, the NRL scientists created a solar cell design that is a potential route to over 50 percent power conversion efficiency under concentrated solar illumination.
Recently awarded a U.S. Department of Energy, Advanced Research Projects Agency-Energy (ARPA-E) project, NRL scientists, working with MicroLink and Rochester Institute of Technology, Rochester, New York, will execute a three year materials and device development program to realise this new solar cell technology.
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www.compoundsemiconductor.net January / February 2013
The purchase was made in the fourth quarter of 2012. Shipment of the systems started in December 2012. Huarong Pan, Chairman of Focus Lightings Tech, comments, “We eagerly await delivery of Aixtron’s latest CRIUS Close Coupled Showerhead (CCS) generation for our future mass production of white-light LEDs. With the system’s low cost of ownership and high productivity as well as Aixtron’s strong customer service in China, the CRIUS II-L systems will increase our competitiveness in the LED market.”
Tim Wang, General Manager at Aixtron China, adds “This new order from Focus Lightings Tech validates the production worthiness of the CRIUS II-L. I am convinced that Focus Lightings will soon benefit from the large production capacity and high throughput on a proven platform, along with the low cost of ownership, presently leading in the industry.” Focus Lightings Tech Inc., located in Suzhou High-tech Industry Park (SIP), Jiangsu province of China specialises in developing and manufacturing high quality LED semiconductor chips, LD laser chips, as well as in semiconductor Lightings and IC products.
At its new plant the company houses chip production lines for red, yellow, blue, green, and white LED lights, as well as an R&D centre that aims to realise 150 LM/W with proprietary technologies for mass production and to successfully step up chip production from 2- to 4-inch substrates.
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