Semiconductor Edge Filter for Broad-Band Multijunction Light Absorption
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Solution Overview
Problem
Current semiconductor DBRs have limited bandwidth and residual reflectivity, which reduces the absorption of longer wavelength light in multijunction solar cells and photodetectors, leading to decreased current generation and efficiency.
Innovation Solution
A semiconductor edge filter is designed to provide high reflectivity (>90%) over a broad wavelength range (>100 nm) and high transmissivity (>95%) at longer wavelengths, allowing for improved absorption in overlying and underlying light absorbing regions without compromising the performance of underlying subcells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a semiconductor DBR is used to reflect light in multijunction solar cells, then reflectivity is improved, but bandwidth is limited and residual reflectivity reduces absorption of longer wavelength light
Solution Approach 1:
The device is segmented into multiple functional layers: a first light absorbing layer, a semiconductor edge filter layer, and a second light absorbing layer. This segmentation allows each layer to perform its specific function - the first layer absorbs higher energy photons, the edge filter reflects specific wavelengths back, and the second layer absorbs lower energy photons, collectively resolving the bandwidth limitation of conventional DBRs
Solution Approach 2:
The semiconductor edge filter acts as an intermediary layer between the first and second light absorbing layers. It mediates the light transmission by reflecting specific wavelength ranges back into the first layer while allowing other wavelengths to pass through to the second layer, thereby extending the effective bandwidth without compromising reflectivity
2Illumination intensity
If a semiconductor DBR is used to reflect light, then reflectivity is improved, but absorption of longer wavelength light decreases due to residual reflectivity
Solution Approach 1:
The semiconductor edge filter exhibits local quality in its optical properties - it provides high reflectivity for specific wavelength ranges (lower energy photons) while providing high transmission for other wavelength ranges (higher energy photons). This spatially selective optical property allows the device to reflect only the necessary wavelengths back into the first light absorbing layer while allowing longer wavelength light to pass through to the second layer for absorption, thereby eliminating the harmful residual reflectivity effect
3Productivity
If the band gap of the bottom junction is increased to absorb more photons, then efficiency is improved, but series resistance losses increase
Solution Approach 1:
The solar cell is divided into multiple junctions with different band gaps, where the top junction has a higher band gap and the bottom junction has a lower band gap. This segmentation allows each junction to operate at optimized current levels, with the top junction absorbing higher energy photons and the bottom junction absorbing lower energy photons, thereby reducing series resistance losses while maintaining high overall efficiency
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 semiconductor edge filter enhances light absorption across a broader wavelength range, increasing the short-circuit current density and overall efficiency of multijunction solar cells and photodetectors, while maintaining performance in underlying subcells.
Implementation Method 1
the semiconductor edge filter reflects a first wavelength range back into the first light absorbing region, that is absorbable by said absorbing region
Implementation Method 2
allows a second wavelength range that is absorbable by an underlying semiconductor to pass through into the second light absorbing region
Implementation Method 3
Each junction in a stack possesses a unique band gap and is optimized for absorbing a different portion of the solar spectrum
Implementation Method 4
In each junction, electron-hole pairs are generated, and current is collected at the ohmic contacts of the solar cell
Implementation Method 5
less energetic photons pass through to the lower junctions where the low energy photons are absorbed
Data Source
AI summary
Semiconductor devices comprising a semiconductor edge filter, a first light absorbing region overlying the semiconductor edge filter and a second light absorbing region underlying the semiconductor edge filter are disclosed. The semiconductor edge filter has a high reflectivity over a first wavelength range absorbed by the overlying light absorbing region and a high transmission over a second wavelength range absorbed by the underlying light absorbing region.