Exponentially Doped Solar Cell Subcells for Efficiency
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Solution Overview
Problem
Existing multijunction solar cells, particularly inverted metamorphic structures, face challenges in achieving commercially viable and energy-efficient power conversion due to limitations in material choice and fabrication steps, which are inadequate for sophisticated applications like satellites requiring improved power and energy efficiency.
Innovation Solution
A method for forming a multijunction solar cell with a specific layer structure including exponentially doped profiles in the base of the lower subcell, using semiconductor materials like InGaP and GaAs, and a metamorphic grading interlayer to enhance lattice mismatch and reduce recombination loss, along with a process involving substrate deposition and removal to optimize the solar cell structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional multijunction solar cell structures are used, then fabrication is simpler, but power and energy conversion efficiency are insufficient for sophisticated applications
Solution Approach 1:
The solar cell is divided into multiple subcells (upper, middle, lower) with different band gaps, each optimized for specific wavelength ranges. This segmentation allows independent optimization of each subcell's doping profile and material composition, achieving high overall conversion efficiency while managing complexity through modular design
Solution Approach 2:
Different regions of the solar cell structure are assigned different doping profiles tailored to local requirements. The upper subcell uses uniform doping, the middle subcell uses exponentially doped profiles, and the lower subcell uses uniformly doped structures. This local optimization of doping characteristics maximizes carrier collection efficiency in each region
2Reliability
If exponentially doped profiles are used in the lower subcell base, then minority carrier collection is improved, but manufacturing complexity increases
Solution Approach 1:
The doping concentration parameter is varied exponentially through the base region thickness, creating a gradient from high to low concentration. This parameter change optimizes the electric field distribution for enhanced minority carrier drift and diffusion, improving collection efficiency while the exponential profile can be achieved through controlled epitaxial growth
3Adaptability or versatility
If metamorphic grading interlayers are used to accommodate lattice mismatch, then material selection flexibility is improved, but fabrication difficulty increases
Solution Approach 1:
A metamorphic grading interlayer is introduced as an intermediary structure between subcells with different lattice constants. This interlayer gradually transitions the lattice constant from one material system to another, accommodating the mismatch and enabling the use of optimal materials for each subcell's band gap requirements while maintaining crystalline quality
4Stability of the object's composition
If inverted metamorphic structure is used, then lattice mismatch management is improved, but commercial viability and energy efficiency are insufficient
Solution Approach 1:
The invention applies different doping strategies to different subcells within the inverted metamorphic structure. The lower subcell base uses exponential doping for optimal carrier collection, while other regions use uniform doping. This localized optimization of doping profiles, combined with the inverted metamorphic architecture, achieves both lattice mismatch management and high energy conversion efficiency for commercial viability
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 method results in a 6.7% increase in current collection and overall efficiency of the solar cell, enhancing radiation hardness and power conversion efficiency suitable for space-related applications, with potential for further improvements in minority carrier collection and long-term performance.
Implementation Method 1
at least the base of the lower subcell has an exponentially doped profile
Implementation Method 2
forming a third solar subcell having a base and an emitter over said grading interlayer having a fourth band gap smaller than said second band gap such that said third subcell is lattice mis-matched with respect to said second subcell
Implementation Method 3
Photovoltaic cells, also called solar cells, are one of the most important new energy sources
Data Source
AI summary
A method of forming a multijunction solar cell including an upper subcell, a middle subcell, and a lower subcell, including providing first substrate for the epitaxial growth of semiconductor material; forming a first solar subcell on the substrate having a first band gap; forming a second solar subcell over the first solar subcell having a second band gap smaller than the first band gap; forming a grading interlayer over the second subcell, the grading interlayer having a third band gap greater than the second band gap; and forming a third solar subcell over the grading interlayer having a fourth band gap smaller than the second band gap such that the third subcell is lattice mis-matched with respect to the second subcell, wherein at least one of the bases of a solar subcell has an exponentially doped profile.