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FOCUS Technology Snapshot - MicroLink's Dual-Junction Photovoltaic Topping Device for High-Temp Operation

MicroLink Devices and the US Naval Research Laboratory (NRL) are collaborating to develop a solar cell for operation at the very high temperature of 400 °C.  This photovoltaic technology will be suitable for integration into a hybrid solar converter to produce both electricity and heat.  If realized, a category of hybrid solar systems with the photovoltaic topping device operating at high temperature will provide solar energy conversion with both high efficiency and dispatchable power.  This will allow an increased grid penetration compared with other solar energy technologies.

The solar cell structure is a dual-junction design, with subcells made from compounds including indium gallium phosphide and gallium arsenide grown epitaxial layer by layer on a gallium arsenide substrate.  Simulations of the solar cell structure under development predict that such a device will be able to convert more than 25% of the power from the incident sunlight to electricity at the operating temperature of 400 °C under optical concentration of 500-suns.  Accelerated lifetime testing will be undertaken using NRL’s extensive thermal testing facilities to develop a cell with a field lifetime greater than 25 years at the proposed operating conditions. 

To substantially reduce the final cost of the solar cell devices, the cost of the GaAs substrate, which accounts for up to 50% of the epitaxial bill of materials, will be reduced using MicroLink’s proprietary epitaxial lift-off and substrate reuse process.  The solar cell wafer is grown on a release layer, which is selectively etched, leaving the substrate and the epitaxial layers intact.  The substrate may then be reused multiple times.