Inverted Metamorphic Multijunction Solar Cell with Single Graded Interlayer
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Solution Overview
Problem
Existing fabrication processes for inverted metamorphic multijunction solar cells using III-V compound semiconductor materials face challenges in producing commercially viable and energy-efficient solar cells due to difficulties in material selection and fabrication steps.
Innovation Solution
A multijunction solar cell structure is developed with a specific sequence of subcells and graded interlayers, including an upper subcell, a middle subcell, a lattice-mismatched subcell, and a lattice-matched subcell, using a surrogate substrate and vapor deposition methods to control lattice constants and electrical properties, enabling efficient energy conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If existing fabrication processes are used for inverted metamorphic multijunction solar cells, then the manufacturing process can be implemented, but the energy conversion efficiency and commercial viability are limited
Solution Approach 1:
The patent inverts the conventional solar cell structure by placing the lattice-matched subcell at the bottom and the lattice-mismatched subcell at the top, allowing the use of a surrogate substrate that can be removed after growth. This inversion enables better material selection for high efficiency while maintaining manufacturability through established vapor deposition techniques.
Solution Approach 2:
The patent introduces a graded interlayer as an intermediary between subcells with different lattice constants. This graded interlayer gradually transitions the lattice constant from one subcell to the next, reducing dislocation density and enabling the integration of lattice-mismatched materials that provide higher energy conversion efficiency.
2Device complexity
If a single metamorphic layer is used to reduce device complexity, then manufacturing becomes easier, but control over lattice constants and electrical properties becomes more difficult
Solution Approach 1:
The patent segments the metamorphic structure into multiple discrete metamorphic layers, each with a specific function. The first metamorphic layer transitions from the surrogate substrate lattice constant to the second subcell lattice constant, while the second metamorphic layer transitions from the second subcell to the third subcell. This segmentation allows independent optimization of each layer's thickness and composition gradient to precisely control lattice constants and electrical properties.
Solution Approach 2:
Each metamorphic layer is designed with locally optimized properties - different thicknesses, different gradient profiles, and different material compositions - to achieve the specific lattice constant transition and electrical characteristics required at each interface in the solar cell stack.
3Loss of energy
If multiple subcells with different band gaps are stacked to improve energy conversion efficiency, then spectral splitting capability increases, but the device structure becomes more complex
Solution Approach 1:
The patent inverts the conventional stacking sequence by placing higher band gap subcells at the bottom and lower band gap subcells at the top, which allows the use of a removable surrogate substrate and simplifies the fabrication process while maintaining the spectral splitting capability for high energy conversion efficiency.
Solution Approach 2:
Graded interlayers are introduced as intermediaries between subcells with different lattice constants, enabling the integration of multiple band gap materials in a controlled manner that manages structural complexity while preserving the spectral splitting function.
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 solution achieves high energy conversion efficiency, with a four-junction solar cell demonstrating an open circuit voltage of approximately 3.265 volts, a short circuit current of 16.26 mA/cm2, a fill factor of 82%, and an efficiency of 32.2%, overcoming previous limitations in commercial viability and efficiency.
Implementation Method 1
a graded interlayer adjacent to the second solar subcell, the graded interlayer having a third band gap greater than the second band gap
Implementation Method 2
using a surrogate substrate and vapor deposition methods to control lattice constants and electrical properties
Implementation Method 3
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
Data Source
AI summary
A multijunction solar cell including an upper first solar subcell having a first band gap; a second solar subcell adjacent to the first solar subcell and having a second band gap smaller than the first band gap; a graded interlayer adjacent to the second solar subcell, the graded interlayer having a third band gap greater than the second band gap; and a third solar subcell adjacent to the graded interlayer, the third subcell having a fourth band gap smaller than the second band gap such that the third subcell is lattice mismatched with respect to the second subcell. A lower fourth solar subcell is provided adjacent to the third subcell and lattice matched thereto, the lower fourth subcell having a fifth band gap smaller than the fourth band gap.