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Epitaxial lift off in inverted metamorphic multijunction solar cells

  • US 8,778,199 B2
  • Filed: 05/07/2012
  • Issued: 07/15/2014
  • Est. Priority Date: 02/09/2009
  • Status: Active Grant
First Claim
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1. A method for manufacturing a solar cell using a process for selectively freeing an epitaxial layer from a single crystal substrate upon which it was grown, comprising:

  • providing a first substrate of gallium arsenide;

    depositing a separation layer on said first substrate;

    depositing on the separation layer a sequence of epitaxial layers of semiconductor material forming a solar cell including;

    forming over the separation layer an upper first solar subcell having a first band gap and including a semiconductor contact layer;

    forming over said first solar subcell a middle second solar subcell having a second band gap smaller than said first band gap;

    forming a graded interlayer over said second solar subcell; and

    forming over said graded interlayer a lower third solar subcell having a fourth band gap smaller than said second band gap such that said third subcell is lattice mismatched with respect to said second subcell;

    mounting the first substrate and the sequence of epitaxial layers of semiconductor material on a flexible film;

    mechanically holding said first substrate against a bottom support of an etching apparatus;

    attaching a connecting link element that connects at least two opposed points on the periphery of the flexible film to an upper portion of the etching apparatus;

    introducing said solar cell having said flexible film bonded thereon into an etchant environment in said etching apparatus;

    etching said separation layer while applying mechanical tension to said connecting link element so as to remove said flexible film with said epitaxial layers from said first substrate;

    attaching the flexible film directly to a surrogate substrate by an electrostatic technique;

    depositing a contact metal layer over the semiconductor contact layer;

    lithographically processing the contact metal layer to form grid lines;

    attaching a cover glass over the grid lines; and

    removing the surrogate substrate.

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