Quantum Dot Subcells for Broadband Solar Absorption
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Solution Overview
Problem
Conventional multi-junction photovoltaic devices face efficiency limitations due to lattice mismatch between dissimilar materials, leading to strain and dislocations, which reduces the overall efficiency of solar energy conversion.
Innovation Solution
The method involves forming semiconductor structures with multiple subcells, each containing quantum dots surrounded by barrier materials with varying effective band-gaps, grown at different temperatures to minimize lattice mismatch and enhance crystal quality, allowing for a broader spectrum of solar energy absorption and conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-layered multi-junction photovoltaic devices are used to absorb broader solar spectrum, then energy conversion efficiency is improved, but lattice mismatch between dissimilar materials causes strain and dislocations reducing device reliability
Solution Approach 1:
The patent changes the structural parameters of the photovoltaic device by introducing quantum dot structures with varying sizes within each subcell. By controlling quantum dot size distribution, the device achieves multiple absorption edges corresponding to different solar energy ranges, thereby expanding the absorption spectrum without requiring excessive material layers that would cause lattice mismatch
Solution Approach 2:
The patent employs composite material structures by combining quantum dot structures with semiconductor matrix materials forming type-II heterostructures. This composite approach enables tailored band-gap engineering where quantum dots with specific compositions and sizes are integrated into a host semiconductor material, achieving both broad spectrum absorption and lattice compatibility
2Adaptability or versatility
If conventional multi-subcell structures with vertically stacked dissimilar materials are used to cover broader solar spectrum, then absorption spectrum is improved, but manufacturing complexity increases due to severe material selection constraints
Solution Approach 1:
The patent segments the absorption function into multiple quantum dot structures with different size distributions within each subcell. Each quantum dot population absorbs a specific wavelength range, and by adjusting size distributions, the device achieves comprehensive solar spectrum coverage. This segmentation approach simplifies manufacturing by using repeated structures rather than requiring precise stacking of many different material layers
Solution Approach 2:
The patent creates universal subcell structures that can absorb multiple wavelength ranges through quantum dot size variation. The same basic subcell design with quantum dot incorporation can be tuned to cover different spectral regions by modifying quantum dot composition and size, reducing the need for completely different material systems for each absorption band
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 enables the fabrication of photovoltaic devices with high-quality crystals and improved efficiency by optimizing the band-gap energies of subcells, thereby increasing the conversion of solar energy into electrical energy across a broader spectrum.
Implementation Method 1
convert solar energy directly into electrical energy. This conversion of energy can be provided utilizing i-type (intrinsic), n-type and p-type conductivity regions in semiconductor materials, thereby producing a photo-voltage potential and a photo-current generated when electron-hole pairs are formed in the semiconductor material
Implementation Method 2
Light with energy above the band-gap will be absorbed, but electron-hole pairs that are created quickly lose their excess energy above the band-gap in the form of heat
Implementation Method 3
These multi-subcell devices utilize various materials having different characteristic band-gap energies so that a wider spectrum of solar energy may be absorbed
Data Source
AI summary
Methods of fabricating photovoltaic devices include forming a plurality of subcells in a vertically stacked arrangement on a semiconductor material, each of the subcells being formed at a different temperature than an adjacent subcell such that the adjacent subcells have differing effective band-gaps. The methods of fabricating also include inverting the structure, attaching another substrate to a second semiconductor material, and removing the substrate. For example, each of the subcells may comprise a III-nitride material, and each subsequent subcell may include an indium content different than the adjacent subcell. Novel structures may be formed using such methods.