# 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.

- **Patent:** US 8912428
- **Original title:** High efficiency multijunction II-VI photovoltaic solar cells
- **Owner:** Epir Technologies
- **Granted:** 2014
- **Status:** Active
- **Times cited:** 2
- **Field:** semiconductors, energy, materials, consumer_electronics

## 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).

## 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.

## Real-world examples

1. High-efficiency solar panels for specialized applications
2. Solar cells used in space satellites
3. Concentrated photovoltaic (CPV) systems

## Why it matters

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.

## 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.

**Full plain-English explainer:** https://patentbrief.org/patent/us/8912428/high-efficiency-multijunction-ii-vi-photovoltaic-solar-cells

**Original patent:** https://patents.google.com/patent/US8912428

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._