Group-IV Heterostructure Solar Cells for Current-Matched Multijunctions
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Solution Overview
Problem
Multijunction solar cells face efficiency limitations due to high series resistance, current mismatching between subcells, and parasitic losses, which hinder the optimization of energy conversion efficiency, especially as the number of subcells increases.
Innovation Solution
The implementation of a photovoltaic cell structure incorporating group-IV subcells with heterojunctions and tunnel junctions, where the group-IV subcells are doped by III-V semiconductor layers to form p-n junctions at the back of the main photoabsorber layer, allowing for better current matching and reduced minority-carrier recombination, and the use of metamorphic or lattice-matched growth techniques to enhance scalability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lattice-matched subcells are used in multijunction solar cells, then manufacturing reliability is improved, but efficiency is limited due to high series resistance and current mismatch
Solution Approach 1:
The patent changes the material parameters by transitioning from traditional lattice-matched III-V subcells to group-IV subcells (Ge, SiGe, SiGeSn) with different lattice constants and bandgaps. This parameter change enables lower series resistance and improved current matching while maintaining manufacturing reliability through controlled epitaxial growth processes.
Solution Approach 2:
The patent employs composite material structures by combining different group-IV materials (Ge, SiGe, SiGeSn) with varying compositions and properties in a single multijunction cell. This composite approach allows optimization of each subcell's electrical and optical characteristics to reduce series resistance and improve overall efficiency.
2Use of energy by moving object
If subcells with large base thicknesses are used, then light absorption is improved, but parasitic losses increase and efficiency decreases
Solution Approach 1:
The patent applies local quality by optimizing the base thickness of each group-IV subcell individually according to its specific bandgap and absorption characteristics. Rather than using uniform thick bases throughout, each subcell's base thickness is locally tailored to maximize light absorption while minimizing parasitic losses in that specific region.
Solution Approach 2:
The patent changes the base thickness parameter for each subcell to optimize the balance between light absorption and parasitic losses. By adjusting this critical dimension parameter for Ge, SiGe, and SiGeSn subcells differently, the design achieves improved efficiency without sacrificing absorption capability.
3Reliability
If conventional tunnel junctions are used for interconnection, then series connection is achieved, but current mismatch and voltage output are limited
Solution Approach 1:
The patent changes the electrical parameters of the tunnel junctions by using group-IV materials with optimized doping concentrations and junction depths. This parameter optimization reduces current mismatch between subcells and enables higher voltage output while maintaining reliable series interconnection.
Solution Approach 2:
The patent uses identical group-IV materials for both the subcell bases and the tunnel junctions, creating a material copying strategy. This approach ensures compatible electrical properties and reduces interface resistance, improving both interconnection reliability and voltage output.
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 results in significantly higher efficiency and voltage for multijunction solar cells, enabling the formation of high-junction cells like 5-junction or 6-junction configurations with improved current balance and reduced series resistance, leading to enhanced energy conversion efficiency.
Implementation Method 1
photovoltaic cells offer a valuable means for providing power generation by converting the abundant resource of the sun's energy to electrical power
Implementation Method 2
managing dopant diffusion
Data Source
AI summary
Photovoltaic cells including a first group-IV subcell including an n-type emitter layer comprising a first group-IV material selected from a first group consisting of Ge, SiGe and SiGeSn, and a second layer comprising a second group-IV material, the second group-IV material being different from the first group-IV material, and the n-type emitter layer being the primary photoabsorber of the first group-IV subcell. A p-n junction of the first group-IV subcell is formed at a heterojunction of the n-type emitter layer and second layer. The photovoltaic cell also includes a tunnel junction, and a second group-IV subcell, the tunnel junction interconnecting the first group IV subcell to the second group-IV subcell, the first group IV subcell and the second group IV subcell being a lowest two subcells of the photovoltaic cell, the first group IV subcell being between the second group-IV subcell and a plurality of HI-V subcells.