Multijunction Metamorphic Solar Cell with Graded DBR
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Solution Overview
Problem
Conventional III-V compound semiconductor multijunction solar cells face challenges in maintaining high energy conversion efficiency over their operational life, especially in space applications, due to factors like radiation exposure and temperature, which affect the band gap and electrical characteristics of subcells, making it difficult to predictably increase power output.
Innovation Solution
A four or five junction solar cell design with a metamorphic buffer layer and a graded DBR structure is implemented, where the average band gap of all subcells is greater than 1.35 eV, and the current through the bottom subcell is intentionally higher than the top subcells at the beginning of life, with a DBR layer between subcells to optimize light reflection and absorption across the solar spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional III-V compound semiconductor multijunction solar cells are used, then high energy conversion efficiency is achieved initially, but efficiency degrades over operational life due to radiation and temperature effects
Solution Approach 1:
The patent changes the band gap parameters of subcells over time by using metamorphic buffer layers with graded composition. The buffer layer composition is designed to compensate for radiation-induced band gap widening, maintaining optimal current matching between subcells throughout the operational life of the solar cell assembly
Solution Approach 2:
The patent applies preliminary action by pre-compensating for future radiation damage through the design of metamorphic buffer layers with specific composition gradients. The buffer layers are designed beforehand to counteract the expected band gap shifts that will occur during space exposure, ensuring stable performance over time
2Reliability
If the average band gap of all subcells is increased above 1.35 eV, then end-of-life efficiency is improved, but beginning-of-life current output may be reduced
Solution Approach 1:
The patent employs parameter changes by designing metamorphic buffer layers with composition gradients that transition the band gap of underlying subcells. This allows the system to operate with higher average band gap values that improve end-of-life efficiency while maintaining acceptable beginning-of-life current output through careful composition control
3Manufacturing precision
If a metamorphic buffer layer with graded composition is used, then lattice matching is improved, but device complexity increases
Solution Approach 1:
The patent uses parameter changes through composition grading in metamorphic buffer layers to achieve lattice matching between subcells with different materials. The gradual composition transition reduces dislocation densities and improves manufacturing precision while managing the inherent complexity through systematic composition control
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 design enhances the end-of-life efficiency of solar cells by optimizing the band gap and current distribution, leading to improved power output and radiation resistance, even after prolonged exposure to space conditions, thereby meeting specific mission requirements for power and efficiency.
Implementation Method 1
a DBR layer between subcells to optimize light reflection and absorption across the solar spectrum
Implementation Method 2
Each subcell is designed to convert photons over different spectral or wavelength bands to electrical current
Data Source
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AI summary
A multijunction solar cell comprising a first solar subcell having a first band gap; a second solar subcell disposed adjacent to said first solar subcell and including an emitter layer, and a base layer having a second band gap less than the first band gap, and being lattice mismatched with the upper first solar subcell, and an intermediate layer directly adjacent to and disposed between first and the second solar subcells and compositionally graded to lattice match the first solar subcell on one side and the second solar subcell on the other side, and arranged so that light can enter and pass through the first solar subcell and at least a portion of which can be reflected back into the first solar subcell by the intermediate layer, and is composed of a plurality of layers of materials with discontinuities in their respective indices of refraction.