Five-Junction Metamorphic Solar Cell With Lower Series Resistance
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Solution Overview
Problem
Multi-junction solar cells with aluminum-containing top cells face efficiency reductions due to increased series resistance and material degradation, particularly in concentrator applications, where high current loads and radiation exposure are prevalent.
Innovation Solution
A stacked, monolithic, upright metamorphic solar cell with five subcells and a metamorphic buffer, where the top subcells have a low aluminum content and a specific band gap structure, ensuring low sheet resistance and high transverse conductivity, is developed. The first subcell is germanium, followed by GaInAs, AlGaInAs, InP, and InP subcells, with a metamorphic buffer adjusting lattice constants to optimize band gaps and reduce series resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If aluminum content is increased in the top two subcells to increase the band gap, then the band gap increases, but the material properties deteriorate and solar cell efficiency reduces
Solution Approach 1:
The patent applies parameter changes by precisely controlling the aluminum content in each subcell to achieve the desired band gap structure without exceeding the threshold that causes material degradation. The top two subcells contain aluminum within specific ranges (0-30% and 0-20% respectively) to maintain both high band gap and good material properties.
Solution Approach 2:
The patent implements local quality by creating different aluminum content distributions across the five subcells. Each subcell has optimized aluminum content tailored to its specific function in the spectrum, with the top subcells having higher aluminum for band gap matching and lower subcells having minimal aluminum to maintain high transverse conductivity and low series resistance.
2Length of moving object
If aluminum is used in the topmost subcell to increase band gap, then the band gap increases, but the mobility of majority charge carriers reduces and sheet resistance increases
Solution Approach 1:
The patent uses parameter changes by limiting aluminum content in the topmost subcell to a maximum of 30%, and in the second subcell to a maximum of 20%. This controlled parameter adjustment achieves sufficient band gap for spectral matching while preventing excessive sheet resistance and maintaining low series resistance under concentration.
Solution Approach 2:
The patent employs composite materials by combining aluminum-containing compounds (AlGaInP, AlGaInAs) with gallium and indium in specific ratios. This creates a composite structure that balances the band gap enhancement from aluminum with the conductivity maintenance from gallium and indium, achieving both high band gap and low series resistance.
3Productivity
If more than three subcells are used to increase efficiency, then the spectral coverage improves, but the complexity of the solar cell structure increases
Solution Approach 1:
The patent applies segmentation by dividing the solar spectrum into five distinct bands, each captured by a dedicated subcell with optimized band gap. This segmentation allows comprehensive spectral coverage from 300nm to 1800nm, converting photons across the entire solar spectrum into electrical current with minimal loss.
Solution Approach 2:
The patent uses another dimension by arranging the five subcells in a vertical stack with different lattice constants (a1 < a2 < a3 < a4 < a5). This dimensional arrangement in the growth direction allows each subcell to be optimized for its specific spectral range while maintaining structural integrity through the lattice constant gradient.
4Length of moving object
If the top cell has high band gap to capture high-energy photons, then the efficiency of high-energy photon conversion improves, but the transverse conductivity decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the aluminum content in the top subcell to a maximum of 30%, which provides sufficient band gap for high-energy photon capture while preventing excessive reduction in transverse conductivity. This parameter optimization ensures both high quantum efficiency and adequate lateral charge transport.
5Manufacturing precision
If lattice-matched multi-junction solar cells are used on germanium substrate, then the manufacturing precision is high, but the spectral coverage is limited
Solution Approach 1:
The patent applies dynamics by transitioning from static lattice-matched structures to a dynamic metamorphic structure where the lattice constant changes progressively through the stack (a1 < a2 < a3 < a4 < a5). This dynamic lattice constant gradient allows each subcell to be optimized for its specific spectral range while maintaining epitaxial growth on the germanium substrate.
Solution Approach 2:
The patent uses composite materials by combining multiple III-V compound semiconductors (GaInP, AlGaInP, GaInAs, AlGaInAs, InP) with different lattice constants. This composite structure enables spectral coverage from 300nm to 1800nm while maintaining compatibility with the germanium substrate through the progressive lattice constant change.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the efficiency of concentrator solar cells by minimizing series resistance losses and maintaining material quality, even under high concentration factors, while reducing shading effects and extending the cell's lifespan.
Implementation Method 1
a metamorphic buffer is arranged between the first subcell and the second subcell, wherein the metamorphic buffer has the first lattice constant on a bottom side facing the first subcell and has the second lattice constant on a top side facing the second subcell
Implementation Method 2
multi-junction solar cells generally comprise three or more subcells with different, matched band gaps, wherein the topmost subcell has the largest band gap and the lowest subcell has the lowest band gap
Data Source
AI summary
A stacked, monolithic, upright metamorphic, terrestrial concentrator solar cell having exactly five subcells and having a metamorphic buffer, wherein a first subcell has a first lattice constant G1 and consists essentially of germanium, a second subcell has a second lattice constant and GaInAs, a third subcell has the second lattice constant G2 and AlGaInAs, a fourth subcell has the second lattice constant G2 and InP, a fifth subcell has the second lattice constant G2 and InP, G1<G2 applies to the lattice constants, the metamorphic buffer is arranged between the first subcell and the second subcell and has the first lattice constant G1 on a bottom side facing the first subcell and the second lattice constant G2 on a top side facing the second subcell, and all of the semiconductor layers of the concentrator solar cell arranged above the first subcell are epitaxially produced on the preceding subcell.