Five-Junction Solar Cell Lattice Matching for Space Radiation
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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 in space environments, due to factors like radiation exposure and temperature, which affect the band gap and open circuit voltage of semiconductor materials.
Innovation Solution
The design incorporates a five-junction solar cell structure with spatially separated semiconductor regions, utilizing high band gap materials for the top subcells and lattice-matched or mismatched subcells to enhance photoconversion efficiency, with the bottom subcell having a significantly higher short circuit current density than the top subcells, and a distributed Bragg reflector layer to optimize light absorption and reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multijunction solar cells are used in space applications, then initial power output can be achieved, but energy conversion efficiency degrades over operational life due to radiation exposure and temperature effects
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the band gap energies of each subcell layer in the multijunction solar cell. The top subcell uses a higher band gap material (e.g., AlInGaP with band gap 2.0-2.2 eV) while lower subcells use progressively lower band gap materials (e.g., InGaAsP with band gap 1.65-1.8 eV, InGaAs with band gap 1.41 eV, and Ge with band gap 0.6-0.9 eV). This gradient structure ensures optimal spectral splitting and maintains high conversion efficiency under space radiation and temperature conditions throughout the operational life.
2Use of energy by moving object
If III-V compound semiconductor multijunction devices are used to achieve higher conversion efficiency, then energy conversion efficiency exceeds 27% under AM0 illumination, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies segmentation by dividing the solar cell into multiple distinct subcell layers, each optimized for specific wavelength ranges. The five-junction structure includes: (1) top subcell with AlInGaP for high energy photons, (2) InGaAsP subcell for mid-energy photons, (3) InGaAs subcell for lower energy photons, (4) Ge subcell for infrared photons, and (5) distributed Bragg reflector layer for light trapping. Each segment handles a specific portion of the solar spectrum, achieving >27% efficiency while managing complexity through functional specialization.
Solution Approach 2:
The patent employs composite materials by combining different III-V compound semiconductor materials with complementary band gap energies in a vertically stacked configuration. The multijunction cell integrates AlInGaP, InGaAsP, InGaAs, and Ge materials, each contributing unique photovoltaic properties. This composite structure enables spectral splitting across the entire solar spectrum, achieving high conversion efficiency by accumulating currents from each material layer.
3Power
If the bottom subcell is designed with higher current density to compensate for degradation, then power output is maintained over time, but current mismatch losses occur in series-connected subcells
Solution Approach 1:
The patent applies local quality by designing each subcell with locally optimized properties matched to its position in the stack and the spectral range it processes. The top subcell (AlInGaP) is optimized for high-energy photons with correspondingly lower current generation, while the bottom Ge subcell handles lower-energy photons with higher current potential. Each subcell's thickness, doping profile, and material composition are locally tuned to generate currents that are naturally balanced in the series connection, eliminating mismatch losses while maintaining high power output.
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 power output and efficiency of the solar cell over its operational life, maintaining high performance even after extended exposure to space radiation and temperature variations, with increased short circuit current density and open circuit voltage, enhancing the power-to-weight ratio and longevity of satellite systems.
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 distributed Bragg reflector layer to optimize light absorption and reflection
Data Source
AI summary
A multijunction solar cell and its method of manufacture including interconnected first and second discrete semiconductor regions disposed adjacent and parallel to each other in a single semiconductor body, including first top subcell, second (and possibly third) lattice matched middle subcells; and a bottom solar subcell adjacent to said last middle subcell and lattice matched thereto; wherein the interconnected regions form at least a four junction solar cell by a series connection being formed between the bottom solar subcell in the first semiconductor region and the bottom solar subcell in the second semiconductor region.