Multijunction Metamorphic Solar Cell Assembly for Space
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Solution Overview
Problem
Current multijunction solar cells face challenges in maintaining high energy conversion efficiency over the operational life of space applications due to factors like radiation exposure and temperature, with complex design variables interacting in unpredictable ways, affecting parameters such as short circuit current density and open circuit voltage.
Innovation Solution
The design involves a five-junction solar cell assembly composed of two four-junction subassemblies with spatially separated semiconductor bodies, where the bottom subcell has a higher short circuit current than the top subcells, and the subcells are lattice mismatched to enhance radiation resistance and temperature stability, with high band gap materials used to maximize efficiency at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multijunction solar cells use complex design variables to maximize energy conversion efficiency, then efficiency improves, but predictability and reliability deteriorate due to unpredictable interactions between design variables
Solution Approach 1:
The solar cell is divided into multiple independent junctions, each with its own set of design variables (band gap, thickness, doping). This segmentation allows each junction to be optimized independently for specific wavelength ranges, improving overall efficiency while making the system more predictable through modular design. The patent implements this by creating a multijunction structure where each junction processes different portions of the solar spectrum independently.
Solution Approach 2:
The patent systematically varies key parameters such as band gap energy, layer thickness, and doping concentrations across different junctions to optimize performance. By changing these parameters in a controlled manner for each junction, the patent achieves high efficiency while maintaining predictability through systematic parameter optimization rather than relying on unpredictable interactions.
2Productivity
If solar cells are designed for high efficiency at beginning of life, then initial performance improves, but performance degradation over operational life in space environment worsens
Solution Approach 1:
The patent incorporates radiation-hardened materials and protective structures in advance to cushion against the harsh space environment. The multijunction design includes junctions with appropriate band gaps that are inherently more resistant to radiation damage, and the structure includes protective layers that shield sensitive regions from degradation over the operational lifetime.
Solution Approach 2:
The patent optimizes parameters such as band gap selection and material composition specifically to maintain performance over time in the space environment. By selecting materials and designing junctions with parameters that are stable under radiation and temperature extremes, the patent ensures both high initial efficiency and sustained performance over the operational life.
3Ease of manufacture
If solar cells use lattice matched subcells, then manufacturing simplicity improves, but radiation resistance and temperature stability worsen
Solution Approach 1:
The patent applies different material compositions and lattice structures to different regions (junctions) of the solar cell based on their specific functional requirements. Each junction is designed with local quality optimized for its role in the spectrum, allowing some junctions to use lattice-matched materials for ease of manufacture while others use materials with superior radiation resistance, achieving both goals through localized optimization.
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 boosts the maximum operational voltage and open circuit voltage, improving the solar cell's efficiency over its operational life, particularly in space environments, by effectively managing the interaction of design variables and enhancing radiation resistance.
Implementation Method 1
The higher conversion efficiency of III-V compound semiconductor solar cells compared to silicon solar cells is in part based on the ability to achieve spectral splitting of the incident radiation through the use of a plurality of photovoltaic regions with different band gap energies, and accumulating the current from each of the regions.
Implementation Method 2
a graded buffer layer composed of indium gallium arsenide and indium aluminum arsenide having a gradual transition in lattice constant from the lattice constant of the germanium substrate to a lattice constant close to that of indium gallium phosphide
Data Source
AI summary
A multijunction solar cell assembly and its method of manufacture including interconnected first and second discrete semiconductor body subassemblies disposed adjacent and parallel to each other, each semiconductor body subassembly including first top subcell, second (and possibly third) lattice matched middle subcells; a graded interlayer adjacent to the last middle solar subcell; and a bottom solar subcell adjacent to said graded interlayer being lattice mismatched with respect to the last middle solar subcell; wherein the interconnected subassemblies form at least a four junction solar cell by a series connection being formed between the bottom solar subcell in the first semiconductor body and the bottom solar subcell in the second semiconductor body.