Graded Window Layer in Multijunction Solar Cells
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Solution Overview
Problem
Current multijunction solar cells face limitations in photoconversion efficiency due to minority carrier recombination at the window layer/emitter layer interface, and the complexity of manufacturing III-V compound semiconductor materials with lattice mismatch issues.
Innovation Solution
A graded composition window layer with varying aluminum content in InAlP or InGaP, where the material at the interface with the emitter layer is in compression and at the top surface is in tension, optimized using x-ray diffraction to measure lattice constant changes, enhancing quantum efficiency by minimizing lattice mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a uniform composition window layer is used, then the manufacturing process is simple, but minority carrier recombination occurs at the interface reducing photoconversion efficiency
Solution Approach 1:
The window layer composition is varied locally through a gradient structure where the aluminum content in InAlP changes continuously from the interface with the emitter layer to the top surface. This local variation in composition allows the material to simultaneously achieve lattice matching at the interface (reducing minority carrier recombination) and provide appropriate mechanical stress distribution, thereby improving photoconversion efficiency without requiring a completely complex multi-layer structure
Solution Approach 2:
The invention changes the compositional parameter of the window layer by implementing a graded structure where the aluminum concentration varies continuously. This parameter change allows the lattice constant to be optimized at different depths - matching the emitter layer at the interface to minimize recombination while maintaining structural integrity throughout the layer, thus resolving the contradiction between manufacturing simplicity and photoconversion efficiency
2Ease of manufacture
If III-V compound semiconductor materials with lattice mismatch are used, then the solar cell can be manufactured, but manufacturing complexity increases due to lattice mismatch issues
Solution Approach 1:
The invention continuously varies the compositional parameter (aluminum content) of the InAlP window layer to create a gradient structure. This gradual parameter change allows the lattice constant to transition smoothly from matching the emitter layer at the interface to providing appropriate mechanical properties at the top surface, thereby simplifying manufacturing by eliminating abrupt interface discontinuities and reducing defects associated with lattice mismatch
Solution Approach 2:
The window layer is formulated as a composite material system with graded composition - InAlP with varying aluminum content - that combines the advantages of lattice matching at the interface with the mechanical stability required for manufacturing. This composite approach with continuous composition variation resolves the lattice mismatch issue while maintaining ease of manufacture through a single integrated layer rather than multiple discrete layers
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 approach increases photoconversion efficiency by reducing minority carrier recombination and optimizing lattice constants, leading to improved energy conversion rates in multijunction solar cells, particularly in high concentration assemblies.
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
the material at the interface between the top surface of the emitter layer of the solar subcell and the bottom of the window is in compression with the emitter, and the material at the top surface of the window layer is in tension
Implementation Method 3
optimized using x-ray diffraction to measure lattice constant changes
Implementation Method 4
optimized using x-ray diffraction to measure lattice constant changes
Data Source
AI summary
A multijunction solar cell including a substrate and at least one solar subcell having an emitter layer, a base layer, and a window layer adjacent to the emitter layer composed of a semiconductor window material, wherein the window material has a graded composition such that the material at the interface between the top surface of the emitter layer of the at least one solar subcell and the bottom surface of the window layer has a compression as measured by a delta in the Bragg angle from the substrate in a range of 0 to 500 arcseconds in compression, and material at the top surface of the window layer has a tension as measured by a delta in the Bragg angle from the substrate in a range of 50 to 700 arcseconds in tension, wherein the delta in the Bragg angle is obtained from a rocking curve from a triple axis coupled scan of Ω and 2θ (omega-2theta) using 1.5406 Å radiation.