Five-Junction Solar Cell Assembly with Interconnected Bottom Subcells
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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, requiring complex design specifications that interact in unpredictable ways, affecting parameters such as short circuit current density and open circuit voltage.
Innovation Solution
The design incorporates a five-junction solar cell assembly composed of two four-junction subassemblies with lattice-mismatched subcells, where the bottom subcell has a higher short circuit current than the top subcells, and the subcells are interconnected to boost operational voltage and efficiency, using high band gap semiconductor materials to enhance photoconversion efficiency at elevated temperatures and over extended operational lifetimes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multijunction solar cells are used, then initial power output is achieved, but energy conversion efficiency degrades over operational life due to radiation and temperature
Solution Approach 1:
The solar cell is divided into multiple junctions (five-junction configuration) with each junction targeting specific spectral bands. The bottom junction is further segmented into two separate semiconductor bodies (Body 1 and Body 2) that are electrically interconnected. This segmentation allows each segment to be optimized for specific wavelength ranges and operational conditions, improving overall efficiency and radiation resistance over time.
Solution Approach 2:
Different junctions use different semiconductor materials with specific band gaps optimized for their spectral regions. The bottom junction employs lattice-mismatched materials (e.g., InGaAs on Ge substrate) with tailored compositions to achieve optimal absorption in the infrared region while maintaining radiation hardness. Each local region of the device has properties customized for its specific function and environmental exposure.
2Productivity
If spectral splitting is used to improve efficiency, then energy conversion efficiency increases, but device complexity increases
Solution Approach 1:
The device is segmented into five distinct junctions, each with specific band gap requirements. The bottom junction is further segmented into two semiconductor bodies that can be designed and fabricated separately using established processes, then interconnected. This segmentation breaks down the complex design into manageable modules with well-defined specifications.
Solution Approach 2:
The patent specifies precise parameter ranges for each junction (band gaps of 0.6-0.9 eV, 1.3-1.4 eV, 1.6-1.8 eV, 2.0-2.2 eV, and 2.4-2.6 eV) to optimize spectral splitting. By establishing clear parameter specifications for each junction, the complex multijunction design becomes more manageable through standardized design rules and fabrication processes.
3Stability of the object's composition
If bottom subcell current is increased to match top subcells, then current uniformity improves, but power output and efficiency decrease
Solution Approach 1:
Instead of increasing the bottom subcell current to match the top subcells (conventional approach), the patent inverts the strategy by allowing the bottom subcell to generate higher current and using electrical interconnection to distribute this excess current to the top subcells. This inversion maximizes power output while achieving current uniformity through the interconnection architecture rather than current limitation.
Solution Approach 2:
The two semiconductor bodies (Body 1 and Body 2) at the bottom junction are electrically merged through interconnections that allow current sharing. This merging enables the bottom junction to operate at optimal current levels for maximum power generation while distributing current uniformly across all five junctions, resolving the contradiction between current uniformity and power output.
4Manufacturing precision
If lattice-matched materials are used, then manufacturing precision is maintained, but photoconversion efficiency at high temperature decreases
Solution Approach 1:
The patent employs lattice-matched materials for upper junctions (where manufacturing precision is critical) and lattice-mismatched materials for the bottom junction (where high-temperature performance and radiation hardness are prioritized). This local differentiation allows optimization for different operational requirements in different regions of the device.
Solution Approach 2:
The solar cell uses a composite structure combining lattice-matched material systems (for upper junctions) with lattice-mismatched material systems (for bottom junction). This composite approach leverages the advantages of both material types: manufacturing precision where needed and high-temperature/radiation performance where needed, achieving overall 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 significantly improves the photoconversion efficiency and operational lifespan of solar cells by increasing the short circuit current of the bottom subcell, enhancing the power output and maintaining efficiency even after prolonged exposure to space radiation and temperature fluctuations.
Implementation Method 1
Solar power from photovoltaic cells, also called solar cells, has been predominantly provided by silicon semiconductor technology
Implementation Method 2
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
Data Source
AI summary
A multijunction solar cell assembly and its method of manufacture including interconnected first and second discreate semiconductor body subassemblies disposed adjacent and parallel to each other, in the sense of the incoming illumination, each semiconductor body subassembly including first top subcell, and possibly third middle subcells and a bottom solar subcell; wherein the interconnected subassemblies form at least a Three junction solar cell by a series connection being formed between the bottom solar subcell in the first semiconductor body with its at least least two junctions and the bottom solar subcell in the second semiconductor body representing the additional junction.