3.2.2 Mechanically Stacked III-V on Silicon Tandem Cells
N.Ekins-Daukes, Xiaojing Hao, Andrew Blakers, S. Bremner
IQE, NREL, Microlink Devices, Airbus
The highest efficiency III-V cells will be achieved using a pristine III-V substrate; however the substrate cost will be prohibitive for all but concentrator and space applications. To retain the highest efficiency performance, while also integrating the solar cell with silicon, two mechanical stack processes are pursued. Both require III-V cells to be released from the substrate and then bonded onto a silicon cell either using an epoxy, or through physical wafer bonding. Both approaches have already demonstrated high efficiency attaining 1-sun efficiencies in excess of 35% on silicon, the challenge remains to make these commercially attractive.
Progress to date
• 33.3% III-V/silicon tandem efficiency with monofacial silicon cell.
• 33.6% to 38.6% III-V/silicon effective tandem efficiency with bifacial silicon cell.
• Progress cost effective methods for recovering an epi-ready surface for wafer reuse.
• Progress III-V devices fabricated from epitaxial templates composed of either silicon, germanium, gallium arsenide or indium phosphide.
• Progress ‘interstitial light-trapping’ that provides wavelength dependant light confinement using epitaxial lift-off devices.
• Progress mechanically stacked III-V/silicon tandem designs and process flows to enhance reproducibility and commercial viability of this approach