Multijunction Solar Cells With Graded Band Gap for Current Collection
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Solution Overview
Problem
Current solar cells for space missions face challenges in maintaining high energy conversion efficiency and radiation resistance over their service life due to complex design requirements and unpredictable interactions with space environmental factors, leading to suboptimal performance and potential failures.
Innovation Solution
A multijunction solar cell design with a graded band gap in the active layer of at least one subcell, increasing the band gap from the top surface to the junction, enhances current collection and radiation performance, optimizing power output and efficiency across various radiation environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multijunction solar cell design with graded band gap is implemented, then current collection and radiation performance are enhanced, but device complexity increases
Solution Approach 1:
The patent applies local quality by implementing a graded band gap structure where the band gap energy varies spatially within the active layer of the solar cell. Different regions of the active layer have different band gap values, with the band gap increasing from the top surface toward the junction. This spatial variation in material property optimizes current collection and radiation performance in different regions without requiring complete redesign of the entire device structure.
Solution Approach 2:
The patent employs parameter changes by systematically varying the band gap energy parameter throughout the active layer thickness. The band gap is engineered to increase gradually from the top surface to the junction, creating a gradient that enhances carrier collection efficiency and radiation hardness. This continuous parameter variation allows optimization of multiple performance metrics simultaneously while managing device complexity through controlled material composition changes.
2Productivity
If the band gap is increased from the top surface to the junction, then power output and efficiency are optimized, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements parameter changes by controlling the composition gradient of the semiconductor material throughout the active layer. By adjusting the relative proportions of constituent elements during deposition, the band gap energy is systematically varied from the top surface to the junction. This compositional gradient enables optimized power output while the manufacturing process is designed to achieve the required precision through controlled deposition conditions and standardized fabrication procedures.
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
The graded band gap design improves the power output and radiation hardness of solar cells, leading to increased efficiency and prolonged performance in space environments, even after exposure to electron or proton radiation.
Implementation Method 1
A multijunction solar cell design with a graded band gap in the active layer of at least one subcell, increasing the band gap from the top surface to the junction
Implementation Method 2
multijunction solar cells... 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
Implementation Method 3
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
Implementation Method 4
each subcell being designed for photons in a specific wavelength band... photons are intended to be captured and converted to electrical energy
Implementation Method 5
III-V compound semiconductor multijunction devices have greater energy conversion efficiencies and generally more radiation resistance... the amount of power provided at the 'end of life' (EOL) which is affected by the radiation exposure of the solar cell over time
Data Source
AI summary
A multijunction solar cell including an upper first solar subcell having a first band gap and positioned for receiving an incoming light beam; and a second solar subcell disposed below and adjacent to and lattice matched with said upper first solar subcell, and having a second band gap smaller than said first band gap; wherein at least one of the solar subcells has a graded band gap throughout the thickness of at least a portion of its emitter layer and base layer.