Graded Buffer Layer for Lattice-Mismatched Solar Cells
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Solution Overview
Problem
Multijunction solar cells face limitations in efficiency and producibility due to the need for nearly perfect lattice matching of subcells and the poor quality of GaInAsN alloy materials, which are challenging to produce with high nitrogen content and lattice-matched conditions.
Innovation Solution
A multijunction solar cell design incorporating a composition-graded buffer layer between subcells allows for lattice-mismatched GaInAsN layers to be optimized in performance without requiring lattice matching, using materials like GaInAsBi, GaInAsSb, and ZnGeAs2, and a substrate with a different lattice parameter, enabling robust deposition and improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lattice-matched GaInAsN alloy is used to achieve desired current match between subcells, then photovoltaic efficiency is improved, but manufacturing difficulty increases due to poor material quality and challenging deposition conditions
Solution Approach 1:
A composition-graded buffer layer is introduced as an intermediary between the substrate and the GaInAsN top subcell. This buffer layer has a composition that gradually changes from lattice-matched to lattice-mismatched, serving as a transition zone that allows the top subcell to be optimized for photovoltaic efficiency without requiring perfect lattice matching to the substrate.
Solution Approach 2:
The lattice parameter of the buffer layer is gradually changed through composition grading. The buffer layer transitions from having the substrate's lattice parameter at the interface with the substrate to having the GaInAsN layer's lattice parameter at the interface with the top subcell, enabling relaxed lattice matching constraints while maintaining material quality.
2Reliability
If GaInAsN alloy with high nitrogen content is used to achieve optimal band gap, then photovoltaic performance is improved, but material quality deteriorates due to difficulty in achieving lattice-matched conditions
Solution Approach 1:
The composition-graded buffer layer acts as a mediator that decouples the nitrogen content optimization from lattice matching constraints. This allows the GaInAsN top subcell to achieve high nitrogen content for optimal band gap and photovoltaic performance while the buffer layer absorbs the lattice mismatch through its graded composition profile.
3Stability of the object's composition
If lattice-matched conditions are enforced for all subcells, then material quality is maintained, but design flexibility is reduced for optimizing current match and efficiency
Solution Approach 1:
Different regions of the solar cell structure are assigned different quality requirements. The buffer layer region accommodates lattice mismatch through composition grading, while the top subcell region is optimized for photovoltaic performance with high nitrogen content. This local differentiation of quality requirements enables both material stability and design flexibility.
Solution Approach 2:
The lattice parameter is changed gradually through the composition-graded buffer layer, transitioning from the substrate's lattice parameter to the GaInAsN layer's lattice parameter. This continuous parameter change enables design flexibility in optimizing the top subcell while maintaining overall material quality through the graded transition.
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 enhances the performance and producibility of multijunction solar cells by allowing for controlled deposition of GaInAsN layers and optimizing subcell performance without the constraints of lattice matching, leading to improved power output and efficiency.
Implementation Method 1
A composition-graded buffer layer lying between the GaInAsN top subcell and the substrate has a composition that is graded from lattice-matched to lattice-mismatched
Implementation Method 2
At each junction, incident light energy, and specifically solar energy, is converted to electrical energy through the photovoltaic effect
Data Source
AI summary
A multijunction solar cell includes a first photoactive subcell layer having a first-subcell lattice parameter and a composition including (a) at least one Group III element, at least one Group V element other than (nitrogen, phosphorus), and (nitrogen, phosphorus), or (b) a material selected from the group including GaInAsBi, GaInAsSb, GaInAsP, ZnGeAs2, or BGaInAs. The multijunction solar cell also has a substrate having a substrate lattice parameter different from the first-subcell lattice parameter, and a composition-graded buffer layer between the first photoactive subcell layer and the substrate and having a buffer-layer lattice parameter graded between the first-subcell lattice parameter and the substrate lattice parameter. The substrate may be a second photoactive subcell layer having a second-subcell lattice parameter different from the first-subcell lattice parameter and sensitive to a second-photoactive-subcell-layer wavelength, and the buffer layer is transparent to the second-photoactive-subcell-layer wavelength.