Distributed Bragg Reflector in Multijunction Solar Cells
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Solution Overview
Problem
Multijunction solar cells for space applications face challenges in optimizing energy conversion efficiency and radiation resistance due to complex interactions between material design parameters, which affect power output and longevity, and existing optical coatings are inefficient at reflecting unused spectral ranges and prone to angle-dependent issues.
Innovation Solution
Incorporating a distributed Bragg reflector (DBR) structure between subcells to reflect light in the 900 to 1050 nm range, reducing absorptance and enabling thermodynamic radiative cooling, while improving power reflection efficiency beyond traditional optical coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional optical coatings are used to reflect unused spectral ranges, then the device complexity is reduced, but the power reflection efficiency is insufficient and angle-dependent issues occur
Solution Approach 1:
The patent employs a distributed Bragg reflector (DBR) structure composed of multiple alternating layers of semiconductor materials with different refractive indices (e.g., AlGaAs and GaAs). This composite layered structure creates constructive interference for reflected light in the 900-1050 nm spectral range, achieving over 190 watts per square meter power reflection efficiency while eliminating the angle-dependent limitations of traditional single-layer optical coatings.
2Loss of energy
If the DBR structure is added to reflect light in the 900 to 1050 nm range, then the power reflection efficiency is improved, but the device complexity increases
Solution Approach 1:
The DBR structure segments the solar cell into distinct functional layers, with each layer in the alternating sequence (high-index and low-index materials) serving a specific optical function. This segmentation allows precise control over the spectral reflection characteristics, targeting the 900-1050 nm range where traditional coatings fail, while the modular layered design facilitates manufacturing through sequential deposition processes.
Solution Approach 2:
The patent applies the DBR structure locally between specific subcells (e.g., between the second and third subcells in a triple-junction cell) rather than across the entire solar cell assembly. This localized application targets the specific spectral gap in the 900-1050 nm range that would otherwise be absorbed uselessly, reducing solar energy absorptance in that particular region while maintaining the overall cell structure.
3Temperature
If the DBR structure is implemented, then thermodynamic radiative cooling is enabled, but the manufacturing precision requirements increase
Solution Approach 1:
The DBR structure enables thermodynamic radiative cooling by changing the optical parameters of the solar cell - specifically, by introducing a reflective layer that redirects absorbed infrared radiation back through the cell, converting heat into electrical energy. This parameter change in the optical properties (adding reflectivity in the 900-1050 nm range) creates a dual benefit: increased power reflection and passive radiative cooling, though it requires precise control of layer thicknesses during manufacturing.
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 DBR structure enhances photoconversion efficiency, reduces solar energy absorptance, and achieves higher power reflection (over 190 watts per square meter), thereby extending the operational life and efficiency of solar cells in space environments.
Implementation Method 1
a distributed Bragg reflector (DBR) structure disposed beneath the base layer of the upper solar subcell and composed of a plurality of alternating layers of different semiconductor materials with discontinuities in their respective indices of refraction and arranged so that light can enter and pass through the upper solar subcell and at least a first portion of the light in a first spectral wavelength range can be reflected back into the upper solar subcell
Implementation Method 2
reflecting light in the spectral range of 900 to 1050 nm which represents unused and undesired solar energy and thereby reducing the overall solar energy absorptance in the solar cell and providing thermodynamic radiative cooling of the solar cell when deployed in space outside the atmosphere
Implementation Method 3
composed of a plurality of alternating layers of different semiconductor materials with discontinuities in their respective indices of refraction and arranged so that light can enter and pass through the upper solar subcell and at least a first portion of the light in a first spectral wavelength range can be reflected back
Data Source
AI summary
A multijunction solar cell and its method of fabrication, including an upper and a lower solar subcell each having an emitter layer and a base layer forming a photoelectric junction; a near infrared (NIR) wideband reflector layer disposed below the upper subcell and above the lower subcell for reflecting light in the spectral range of 900 to 1050 nm which represents unused and undesired solar energy and thereby reducing the overall solar energy absorptance in the solar cell and providing thermodynamic radiative cooling of the solar cell when deployed in space outside the atmosphere.