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semiconductor. If, on the other hand, the layer is too thick, it prevents corrosion but also blocks the semiconductor from absorbing light and keeps electrons from passing through to reach the catalyst that drives the reaction.
At Caltech, the researchers used a process called atomic layer deposition to form a layer of titanium dioxide (TiO2) - a material found in white paint and many toothpastes and sunscreens - on single crystals of GaAs, GaP or silicon.
to weeks,” says Lewis. “That’s the next step.”
The work is described in the paper, “Amorphous TiO2 Coatings Stabilize Si, GaAs, and GaP Photoanodes for Efficient Water Oxidation,” by Hu et al in Science, 344 (6187), pp. 1005-1009. DOI: 10.1126/science.1251428
The research was supported by the Office of Science of the U.S. Department of Energy through an award to JCAP, a DOE Energy Innovation Hub. Some of the work was also supported by the Resnick Sustainability Institute and the Beckman Institute at Caltech.
First Solar to introduce pre-engineered CdTe plant products
The new offerings focus on customers’ need for enhanced, reliable energy output and will be introduced at Intersolar Europ
First Solar has launched its modular AC Power Block solar power plant solution and its next generation First Solar Series 4 thin film photovoltaic (PV) module.
Scanning electron microscope (SEM) image of nickel islands on silicon protected by a titanium dioxide film (Credit: Shu Hu/ Caltech)
The key was that they used a form of TiO2 known as “leaky TiO2” - because it leaks electricity. First made in the 1990s as a material that might be useful for building computer chips, leaky oxides were rejected as undesirable because of their charge- leaking behaviour.
However, leaky TiO2 seems to be just what was needed for this solar-fuel generator application. Deposited as a film, ranging in thickness between 4 and 143nm, the TiO2 remained optically transparent on the semiconductor crystals - allowing them to absorb light - and protected them from corrosion but allowed electrons to pass through with minimal resistance.
On top of the TiO2, the researchers deposited 100nm-thick “islands” of an abundant, inexpensive nickel oxide material that successfully catalyzed the oxidation of water to form molecular oxygen.
The work appears to now make a slew of choices available as possible light-absorbing materials for the oxidation side of the water-splitting equation. However, the researchers emphasise, it is not yet known whether the protective coating would work as well if applied using an inexpensive, less-controlled application technique, such as painting or spraying the TiO2 onto a semiconductor. Also, thus far, the Caltech team has only tested the coated semiconductors for a few hundred hours of continuous illumination.
“This is already a record in terms of both efficiency and stability for this field, but we don’t yet know whether the system fails over the long term and are trying to ensure that we make something that will last for years over large areas, as opposed
Purpose-built for power plant owners and developers seeking to minimise project risk and maximise energy production and revenue, the AC Power Block is a configurable system solution that can be scaled to address a wide range of project conditions.
The pre-engineered system is available in modular units ranging from 800 kilowatts (kW) to 3.8 megawatts (MW). Based on First Solar’s PV plant design and energy prediction model, the AC Power Block is backed by a first year energy performance guarantee and a 25-year capacity warranty.
AC Power Block solution
First Solar’s new Series 4 PV module offers up to eight percent more energy than conventional crystalline silicon modules with the same power rating, and is compatible with advanced 1500-volt plant architectures. The Series 4A variant features a new anti-reflective coated glass, which enhances energy production. The module is backed by First Solar’s 25-year Linear Performance Warranty.
June 2014
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