Compound Semiconductor-Based Thin-Film and Flexible Optoelectronics
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Compound semiconductors are the basis for many of the highest performance optical and electronic devices in use today. Their widespread commercial application has, however, been limited due to the high cost of substrates. Device costs can, therefore, be significantly reduced if the substrate can be reused in a simple, totally non-destructive and rapid process. Here, we present a method that allows for the indefinite reuse and recycling of wafers, employing a combination of epitaxial "protection layers" that return the wafers to their original, pristine and epi-ready condition following epitaxial layer removal and adhesive-free bonding to a secondary plastic substrate. The generality of this process was confirmed by fabricating high performance GaAs-based photovoltaic cells, light emitting diodes, and metal-semiconductor field effect transistors that are transferred, without loss of performance, onto flexible and lightweight plastic substrates, and then the parent wafer is recycled for subsequent growth of additional device layers.
Furthermore, we present an approach based on thin-film gallium arsenide (GaAs) solar cells that can achieve extremely low-cost solar energy conversion with an estimated cost of only 3% of conventional GaAs solar cells using an accelerated, non-destructive epitaxial lift-off (ND-ELO) wafer recycling process integrated with a lightweight, thermoformed plastic, truncated mini-compound parabolic concentrator (CPC) that avoids the need for active solar tracking. Using solar cell/CPC assemblies whose orientation is adjusted only a few times per year, the annual energy harvesting is increased by 2.8 times compared with planar solar cells without solar tracking. These results represent a potentially drastic cost reduction in both the module and balance of systems costs compared with heavy, rigid conventional modules and trackers that are subject to wind loading damage and high installation costs.
The low cost and high performance thin-film based optoelectronics provide an opportunity to open a completely new domain of device applications by escaping from its planar and rigid geometry to a flexible and conformal one.