Graded Interlayer for Inverted Metamorphic Multijunction Solar Cells
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Solution Overview
Problem
Existing solar cell technologies, particularly inverted metamorphic multijunction solar cells, face challenges in achieving commercially viable and energy-efficient performance due to inadequate materials and fabrication steps, which hinder their application in sophisticated applications like satellite power systems.
Innovation Solution
A method for forming multijunction solar cells involving a bottom subcell with a bandgap of 0.8 to 1.2 eV, a heterojunction middle subcell with a higher bandgap, and a homojunction top subcell, with a continuously-graded or step-graded interlayer of InGaAlAs that maintains a constant bandgap of 1.5 eV, lattice matching the middle and bottom subcells, using metal organic chemical vapor deposition (MOCVD) to precisely control the mole fractions of In, Ga, and Al.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional materials and fabrication steps are used in inverted metamorphic multijunction solar cells, then manufacturing simplicity is maintained, but energy conversion efficiency and commercial viability are insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition gradients of the metamorphic layer (varying InGaAsP mole fractions) and bandgap engineering of subcells to optimize light absorption across different wavelengths. This enables improved energy conversion efficiency while maintaining a systematic fabrication approach using standard MOCVD equipment.
Solution Approach 2:
The patent employs composite materials through the metamorphic layer consisting of multiple semiconductor compounds (InGaAsP with varying compositions) stacked in a graded structure. This composite approach allows lattice matching between subcells with different bandgaps, enabling efficient multi-junction operation while using conventional MOCVD fabrication processes.
2Device complexity
If inadequate materials and fabrication steps are used, then device complexity is reduced, but photocurrent generation and open circuit voltage are insufficient for sophisticated applications
Solution Approach 1:
The patent segments the solar cell into multiple functional subcells (top subcell with higher bandgap, bottom subcell with lower bandgap) separated by a metamorphic layer. Each subcell is optimized for specific wavelength ranges, enabling enhanced photocurrent generation through multi-junction architecture while maintaining manageable device complexity.
Solution Approach 2:
The metamorphic layer acts as an intermediary between subcells with different lattice constants. It provides gradual lattice constant transition and dislocation filtering, enabling efficient carrier transport and high open circuit voltage while allowing the use of sophisticated material compositions for enhanced power generation.
3Adaptability or versatility
If lattice mismatched subcells are used to increase bandgap variation, then spectral coverage is improved, but dislocation density and dark saturated current increase
Solution Approach 1:
The patent applies local quality by creating a graded metamorphic layer where the lattice constant and composition vary gradually from one subcell to another. This localized gradient structure allows each region to be optimized for its specific function while maintaining overall lattice compatibility, reducing dislocation density despite large bandgap variations for enhanced spectral coverage.
Solution Approach 2:
The patent uses parameter changes by continuously varying the InGaAsP composition parameters (mole fractions of In, Ga, As, P) through the metamorphic layer thickness. This gradual parameter transition enables lattice matching between subcells with different bandgaps, achieving broad spectral coverage while minimizing dislocation formation and dark saturated current.
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 photocurrent generation, increases open circuit voltage, and reduces dark saturated current, resulting in improved energy conversion efficiency and commercially viable solar cells suitable for advanced applications.
Implementation Method 1
selecting a reaction time and temperature and a flow rate for each source gas to form the graded interlayer disposed on the bottom subcell
Implementation Method 2
forming a bottom subcell having a bandgap in the range of 0.8 to 1.2 eV; forming a heterojunction middle subcell having a base and emitter, a bandgap greater than the bandgap of the bottom subcell
Data Source
AI summary
Inverted metamorphic multijunction solar cells having a heterojunction middle subcell and a graded interlayer, and methods of making same, are disclosed herein. The present disclosure provides a method of manufacturing a solar cell using an MOCVD process, wherein the graded interlayer is composed of (InxGa1-x)y Al1-yAs, and is formed in the MOCVD reactor so that it is compositionally graded to lattice match the middle second subcell on one side and the lower third subcell on the other side, with the values for x and y computed and the composition of the graded interlayer determined so that as the layer is grown in the MOCVD reactor, the band gap of the graded interlayer remains constant at 1.5 eV throughout the thickness of the graded interlayer.