{
  "patent_number": "US 8912428",
  "country": "US",
  "title": "Solar Cells Made of Stacking Layers with Different Energy Gaps",
  "original_title": "High efficiency multijunction II-VI photovoltaic solar cells",
  "summary": "This patent describes a solar cell built by stacking multiple layers, each designed to capture a different part of the light spectrum for maximum energy conversion, achieving high efficiency.",
  "what_it_does": "This patent details a special kind of solar cell called a monolithic multijunction photovoltaic solar cell. It's built by stacking up to five layers, called subcells, on top of each other. The bottom-most subcell uses a base made of silicon, germanium, or a mix, acting as the foundation. Above this, subsequent subcells are made from different II-VI semiconductor materials, like CdTe or CdSe. Crucially, each layer is designed to capture light of a specific color (wavelength) based on its 'band gap' energy. The layers are arranged so that the band gap gets smaller as you go up the stack, meaning each layer is optimized for a different part of the light spectrum. The patent also specifies that the thickness of each subcell is precisely controlled so that they all generate roughly the same amount of electrical current, which is key to maximizing the overall power output. Claim 1 highlights that this design aims for an ideal series efficiency of at least 40% under concentrated sunlight (500 suns).",
  "what_it_does_not_cover": [
    "Solar cells that do not use at least two stacked subcells.",
    "Solar cells where the bottom-most subcell base is not made of a Group IV semiconductor like silicon or germanium.",
    "Solar cells where the stacked subcells are not made from Group II-VI semiconductor materials.",
    "Solar cells where the band gap of the stacked subcells does not progressively decrease from bottom to top.",
    "Solar cells that do not optimize subcell thickness for equal current generation across all subcells.",
    "Solar cells designed for standard, non-concentrated sunlight conditions (less than 500 suns)."
  ],
  "filed": "2008-10-30",
  "granted": "2014-12-16",
  "expires": "2028-10-30",
  "status": "active",
  "holder": "Epir Technologies",
  "holder_url": "https://patentbrief.org/company/epir-technologies",
  "inventors": [
    {
      "name": "Sivalingam Sivananthan",
      "url": "https://patentbrief.org/inventor/sivalingam-sivananthan"
    },
    {
      "name": "Christoph GREIN",
      "url": "https://patentbrief.org/inventor/christoph-grein"
    },
    {
      "name": "James W. GARLAND",
      "url": "https://patentbrief.org/inventor/james-w-garland"
    },
    {
      "name": "Wayne H. Lau",
      "url": "https://patentbrief.org/inventor/wayne-h-lau"
    }
  ],
  "times_cited": 2,
  "tags": [
    "semiconductors",
    "energy",
    "materials",
    "consumer_electronics"
  ],
  "abstract": "A Group II-VI photovoltaic solar cell comprising at least two and as many as five subcells stacked upon one another. Each subcell has an emitter layer and a base layer, with the base of the first subcell being made of silicon, germanium, or silicon-germanium. The remaining subcells are stacked on top of the first subcell and are ordered such that the band gap gets progressively smaller with each successive subcell. Moreover, the thicknesses of each subcell are optimized so that the current from each subcell is substantially equal to the other subcells in the stack. Examples of suitable Group II-VI semiconductors include CdTe, CdSe, CdSeTe, CdZnTe, CdMgTe, and CdHgTe.",
  "url": "https://patentbrief.org/patent/us/8912428/high-efficiency-multijunction-ii-vi-photovoltaic-solar-cells",
  "markdown_url": "https://patentbrief.org/patent/us/8912428/high-efficiency-multijunction-ii-vi-photovoltaic-solar-cells/md",
  "google_patents_url": "https://patents.google.com/patent/US8912428",
  "relatedPatents": []
}