Multijunction Solar Cell Band Gap Grading for Space Radiation
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Solution Overview
Problem
Current multijunction solar cells for space applications face challenges in maximizing energy conversion efficiency and radiation resistance due to complex design parameters and unpredictable interactions between material variables, leading to suboptimal power output and efficiency degradation over time.
Innovation Solution
A multijunction solar cell design featuring a graded band gap in the active layer of at least one subcell, increasing the band gap from the top surface to the junction, which enhances current collection and radiation performance, optimizing power output and efficiency across various radiation environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multijunction solar cell design is used, then manufacturing complexity is reduced, but energy conversion efficiency and radiation resistance are suboptimal
Solution Approach 1:
The patent applies parameter changes by implementing a graded band gap structure in the active layer, where the band gap energy varies continuously from the top surface to the junction. This gradient parameter modification optimizes both current collection and radiation resistance simultaneously, resolving the contradiction between improved reliability and increased design complexity.
Solution Approach 2:
The patent implements local quality by creating different band gap values at different positions within the active layer. The band gap is engineered to be higher near the junction and lower at the top surface, allowing each region to perform its specific function optimally - enhancing both efficiency and radiation hardness without requiring complex external systems.
2Power
If spectral splitting with multiple photovoltaic regions is implemented, then energy conversion efficiency is improved, but device complexity increases
Solution Approach 1:
The patent merges the functions of multiple photovoltaic regions with different band gaps into a single graded band gap active layer. Instead of stacking separate junctions, the band gap varies continuously throughout one layer, achieving spectral splitting and current accumulation benefits while simplifying the overall device structure and reducing manufacturing complexity.
Solution Approach 2:
The patent transitions from a discrete multi-junction structure (stacking layers in one dimension) to a continuous graded band gap structure (varying properties through the layer thickness). This dimensional approach to band gap engineering achieves similar efficiency benefits with reduced structural complexity by utilizing the vertical dimension of a single active layer.
3Reliability
If band gap is increased to improve radiation hardness, then radiation resistance is improved, but current collection decreases
Solution Approach 1:
The patent resolves this contradiction by implementing a graded band gap parameter that varies continuously through the active layer. The band gap is higher near the junction to enhance radiation hardness and lower at the top surface to improve photon absorption and current generation. This spatially varying parameter approach optimizes both competing requirements simultaneously.
Solution Approach 2:
The patent applies local quality by assigning different band gap values to different regions of the active layer. The region near the junction has higher band gap for radiation resistance, while the top region has lower band gap for current collection. This localized optimization of material properties eliminates the need to choose between the two competing performance metrics.
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 increases the short circuit current and fill factor, resulting in improved power output and radiation hardness, enhancing the solar cell's performance both initially and at the end of its service life in space environments.
Implementation Method 1
multijunction solar cells... spectral splitting of the incident radiation through the use of a plurality of photovoltaic regions with different band gap energies
Implementation Method 2
III-V compound semiconductor multijunction devices have greater energy conversion efficiencies and generally more radiation resistance
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.