Low-Cost, Manufacturable, 6-Inch Wafer Bonding Process for Next-Generation 5-Junction IMM+Ge Photovoltaic Devices
Project Description
To continue the trend towards ever more efficient photovoltaic devices, next-generation multi-junction cells will be based on increasingly complex structures. These structures will require the ability to join two or more independently grown epitaxial structures together via wafer bonding which is a complicated process to include in a high-volume manufacturing environment using conventional wafer fusion techniques. Additionally, metamorphic material is very difficult to bond due to the inherent roughness of the surface. We propose the development of a bonding process based on an epoxy interface with an embedded metallic grid to provide electrical conductivity across the bonded interface. This process is expected to be low-cost, compatible with metamorphic material and high-volume manufacturing, and readily scalable to 6-inch or larger substrates. It will be an enabling technology for next-generation, five- and six-junction solar cells with 1-sun AM0 efficiency exceeding 37% in high volume production. An example device structure that can benefit from the proposed wafer bonding technique is a six-junction solar cell. This six-junction device is composed of two triple-junction stacks, one of which is grown on a GaAs substrate while the other is grown on an InP substrate. The two triple-junction stacks must be bonded together to form the final six-junction device. The epoxy-bonding process proposed here will allow this bonding to be accomplished reliably on large-area substrates. This is essential for turning this structure into a practical, manufacturable, commercial product. When coupled with MicroLink Device's proprietary epitaxial lift-off (ELO) technology which allows for reuse of both the GaAs and InP substrates, devices based on this six-junction architecture could potentially be manufactured for less than $170/W in sufficient volume to serve near-term applications. This structure is expected to yield 40% efficiency under AM0 illumination.
More »Anticipated Benefits
The ultra-high-efficiency, extremely lightweight cells that can be created using this technology are potentially beneficial to NASA for any space-based application in which weight, efficiency, and reliability are of the utmost importance. In particular, next-generation solar electric propulsion (SEP) systems which rely on extremely large arrays of powerful solar cells stand to benefit substantially from the improvements offered by this technology.
The proposed technology will allow next-generation solar cells exceeding 40% AM0 efficiency to be made commercially available. This process is compatible with MicroLink's existing epitaxial lift-off (ELO) technology which means they can also be made exceptionally light-weight. Non-NASA potential customers include makers of UAVs, such as Aerovironment, Aurora Flight Sciences, and EADS-Astrium, who could use the cells to substantially increase the endurance of the UAV. High-efficiency is particularly critical to UAV applications as the are available for solar cells is limited to the wing surface of the vehicle. Weight is another critical consideration for UAVs as the additional weight of the solar cells limits the advantage gained by using them. Another category of potential customers includes companies such as Power Film who make solar sheets and solar blankets for collection of solar energy for high value terrestrial applications.
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Primary U.S. Work Locations and Key Partners
| Organizations Performing Work | Role | Type | Location |
|---|---|---|---|
| MicroLink Devices, Inc. | Lead Organization |
Industry
Minority-Owned Business
|
Niles, Illinois |
Glenn Research Center
(GRC)
|
Supporting Organization | NASA Center | Cleveland, Ohio |
Primary U.S. Work Locations
-
Illinois
-
Ohio
