Graded Band Gap Multijunction Solar Cells for Radiation Resistance
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Solution Overview
Problem
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 at least one subcell, with an alternating increase and decrease in band gap adjacent to the junction, optimized for specific radiation environments, to enhance current collection and radiation performance, while maintaining a constant lattice constant and improving Fill Factor and open-circuit voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multijunction solar cell design with constant band gap is used, then the manufacturing process is simpler, but the power output and radiation resistance are suboptimal
Solution Approach 1:
The patent applies local quality by implementing a graded band gap structure where the band gap energy varies spatially across the subcell thickness. Specifically, the band gap is higher at the junction interface and lower at the bulk region, creating localized variations in electronic properties that optimize both current collection and radiation resistance without requiring complete redesign of the entire device architecture
Solution Approach 2:
The patent changes the band gap parameter from a constant value to a graded distribution. By controlling the composition gradient of the semiconductor material (e.g., varying InGaAsP composition), the band gap energy is systematically varied through the layer thickness, enabling improved power output and radiation performance while maintaining a manageable manufacturing process
2Reliability
If the band gap is increased to improve radiation resistance, then the radiation performance improves, but the current collection efficiency decreases
Solution Approach 1:
The patent resolves this contradiction by applying different band gap values at different locations: a higher band gap at the junction region to enhance radiation resistance and carrier separation, and a lower band gap in the bulk region to improve photon absorption and current generation. This spatial differentiation of material properties optimizes both competing requirements
Solution Approach 2:
The subcell is segmented into regions with different band gap characteristics - a graded region near the junction with higher band gap and a bulk region with lower band gap. This segmentation allows each region to perform its specialized function: the graded region handles radiation resistance and carrier separation, while the bulk region handles efficient light absorption and current generation
3Power
If a graded band gap structure is implemented to optimize power output, then the Fill Factor and open-circuit voltage improve, but the manufacturing complexity increases
Solution Approach 1:
The patent implements parameter changes by systematically varying the semiconductor composition during the epitaxial growth process. By controlling the gradient of group III elements (In, Ga, Al) and group V elements (As, P), the band gap is graded through the layer, achieving improved Fill Factor and open-circuit voltage while using established manufacturing techniques
Solution Approach 2:
The graded band gap structure acts as an intermediary between the incident photons and the electrical output. The gradual composition transition serves as a mediator that smoothly transforms the optical energy across different wavelengths into electrical current, improving power extraction efficiency while maintaining compatibility with existing solar cell fabrication processes
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 power output and radiation resistance, optimizing solar cell performance for various space missions by enhancing current collection and maintaining efficiency over the solar cell's operational life.
Implementation Method 1
a multijunction solar cell comprising: an upper first solar subcell; a second solar subcell adjacent to the first solar subcell, wherein the emitter and base layers of the second solar subcell form a photoelectric junction
Implementation Method 2
the base and emitter layer of at least one of the subcells has a graded band gap throughout at least a portion of the thickness of its active layer with a band gap adjacent the junction in the range of 20 to 300 meV greater than the band gap away from the junction
Data Source
AI summary
A multijunction solar cell including an upper first solar subcell having an emitter and base layers forming a photoelectric junction; a second solar subcell disposed under and adjacent to the upper first solar subcell, and having an emitter and base layers forming a photoelectric junction; and a third solar subcell disposed under and adjacent to the second solar subcell and having an emitter and base layers forming a photoelectric junction; wherein at least one of the base and emitter layers of at least a particular solar subcell from among the upper first solar subcell, the second solar subcell, and the third solar subcell has a graded band gap throughout at least a portion of thickness of its active layer adjacent to the photoelectric junction and being in a range of 20 to 300 MeV greater than a band gap in the active layer away from the photoelectric junction.