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 satellite systems, particularly due to factors like radiation exposure and temperature, which affect the band gap and electrical properties of semiconductor materials, leading to inefficiencies in power output.
Innovation Solution
The design involves interconnecting spatially split multijunction solar cell subassemblies with high band gap semiconductor materials, specifically a five-junction solar cell configuration where the bottom subcell has a significantly higher short circuit current than the top subcells, and the use of lattice mismatched subcells to enhance photoconversion efficiency and operational voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional silicon solar cells are used, then manufacturing simplicity is maintained, but energy conversion efficiency is limited to about 18%
Solution Approach 1:
The solar cell is divided into multiple subcells stacked vertically, each subcell targeting a specific spectral band. This segmentation allows each subcell to be optimized for its wavelength range, achieving over 27% energy conversion efficiency by capturing photons across different energy levels that a single silicon junction cannot efficiently convert.
Solution Approach 2:
The patent employs composite semiconductor materials with different band gap energies arranged in a vertical stack. Each subcell uses materials specifically selected for its spectral response, creating a composite structure that converts a broader portion of the solar spectrum into electrical energy, resolving the efficiency limitation of single-material silicon cells.
2Manufacturing precision
If III-V compound semiconductor multijunction cells are used, then energy conversion efficiency exceeds 27%, but manufacturing complexity increases
Solution Approach 1:
By segmenting the multijunction cell into distinct subcells with specific material compositions, the patent simplifies the manufacturing process. Each subcell can be fabricated using optimized processes for its specific material system, making the complex III-V compound semiconductor manufacturing more manageable and scalable.
Solution Approach 2:
The patent optimizes key parameters such as subcell thickness, doping concentrations, and band gap energies to achieve the desired efficiency while simplifying manufacturing. By carefully selecting and adjusting these parameters, the complex multijunction structure becomes more manufacturable without sacrificing the >27% efficiency target.
3Power
If solar cells are designed for maximum initial power output, then power-to-weight ratio is improved, but lifetime efficiency and end-of-life power output decrease
Solution Approach 1:
The patent adjusts subcell design parameters including thickness, material composition, and band gap to optimize performance across the entire operational lifetime. This ensures high power-to-weight ratio at deployment while maintaining robustness against radiation and temperature effects, preserving efficiency at end-of-life.
Solution Approach 2:
The multijunction structure inherently provides cushioning against degradation by distributing the photon absorption across multiple subcells. This design anticipates radiation damage and temperature effects, allowing the cell to maintain higher efficiency over time compared to single-junction cells, thus improving lifetime efficiency.
4Ease of manufacture
If subcells are designed with equal current densities, then manufacturing is simplified, but photoconversion efficiency is reduced
Solution Approach 1:
The patent applies local quality by allowing different current densities in different subcells based on their specific optical and electrical characteristics. Each subcell is optimized independently for its spectral band, with current densities adjusted to match the photon flux and energy conversion potential of its specific wavelength range, maximizing overall photoconversion efficiency.
Solution Approach 2:
By changing the current density parameter across different subcells rather than maintaining uniform values, the patent achieves higher photoconversion efficiency. Each subcell's current density is optimized for its specific band gap and spectral response, improving overall cell performance while remaining manufacturable through controlled parameter variation.
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 improves the photoconversion efficiency and maintains high power output over the operational life of satellite systems, even under high temperature and radiation conditions, by boosting the maximum operational voltage and open circuit voltage, and ensuring efficient energy conversion across the solar spectrum.
Implementation Method 1
III-V compound semiconductor multijunction devices have greater energy conversion efficiencies... 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
Data Source
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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.