Solar Cells Made of Stacking Layers with Different Energy Gaps
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.
Original patent title: “High efficiency multijunction II-VI photovoltaic solar cells”
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. Granted to Epir Technologies in 2014 with 17 claims and 2 forward citations, and it is expected to expire in 2028.
Coverage
What does this patent actually cover?
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. ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1 highlights that this design aims for an ideal series efficiency of at least 40% under concentrated sunlight (500 suns).
The gap
What does this patent 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).
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The innovation lies in precisely engineering the stack of materials – starting with a Group IV semiconductor base and layering Group II-VI semiconductors with progressively smaller band gaps – and optimizing the thickness of each layer to ensure balanced current generation. This coordinated design maximizes the capture of diverse light wavelengths and minimizes energy loss.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
High-efficiency solar panels for specialized applications
Solar cells used in space satellites
Concentrated photovoltaic (CPV) systems
Why it matters
The bigger picture
This patent is significant because it addresses the fundamental challenge of improving solar cell efficiency beyond the limits of single-junction cells. By stacking multiple materials with different light absorption properties, it allows for a much broader capture of the solar spectrum. This technology is crucial for applications where high efficiency is paramount, such as in space or concentrated solar power systems, pushing the boundaries of renewable energy generation.
Filed
October 30, 2008
Granted
December 16, 2014
Market context
Who's building on this
Companies in this space
While Epir Technologies was the assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →, the development of advanced multijunction solar cells is a field pursued by several research institutions and specialized companies. Companies like Spectrolab (a Boeing subsidiary) and Alta Devices are known for high-efficiency multijunction cells, often for aerospace and specialized terrestrial markets.
Market impact
Patents like this contribute to the ongoing advancement of photovoltaic technology, enabling higher efficiency solar cells that can be critical for niche markets like aerospace and concentrated solar power. While not directly leading to mass-market solar panel dominance, they drive innovation in materials science and device engineering that can trickle down to broader applications.
Claim 1 — Plain English
What this patent covers
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).
The clever bit
The innovation lies in precisely engineering the stack of materials – starting with a Group IV semiconductor base and layering Group II-VI semiconductors with progressively smaller band gaps – and optimizing the thickness of each layer to ensure balanced current generation. This coordinated design maximizes the capture of diverse light wavelengths and minimizes energy loss.
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).
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
PatentBrief Score
Impact Score
Early stage
Citation count
10/40
Early citations
Claim breadth
11/20
Broad claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
5/20
Granted 10–20 years ago
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$27K – $87K
Midpoint $55K · 2.3 yr remaining · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
17 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Sivananthan, S., GREIN, C., GARLAND, J. W., & Lau, W. H. (2014). Solar Cells Made of Stacking Layers with Different Energy Gaps (U.S. Patent No. 8,912,428). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/8912428/high-efficiency-multijunction-ii-vi-photovoltaic-solar-cells
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does Solar Cells Made of Stacking Layers with Different Energy Gaps cover?
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.
Who owns patent US 8912428?
Epir Technologies owns this patent, granted in 2014.
When does this patent expire?
This patent is expected to expire on October 30, 2028, when the invention enters the public domain.
What is patent US 8912428 cited by?
This patent has been cited by 2 later patents that build on its ideas.
What problem does this patent solve?
This patent is significant because it addresses the fundamental challenge of improving solar cell efficiency beyond the limits of single-junction cells. By stacking multiple materials with different light absorption properties, it allows for a much broader capture of the solar spectrum. This technology is crucial for applications where high efficiency is paramount, such as in space or concentrated solar power systems, pushing the boundaries of renewable energy generation.
What does this patent NOT cover?
Solar cells that do not use at least two stacked subcells.
Patent monitoring