Group-IV Solar Cell Heterostructures for Multijunction Efficiency
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Solution Overview
Problem
Multijunction photovoltaic cells face efficiency limitations due to the requirement of low resistance interfaces and the need for current matching among subcells, which restricts the number of subcells and leads to parasitic losses, especially with high current densities and low voltages resulting in power loss and impaired radiation resistance.
Innovation Solution
The use of group-IV solar cells with varying energy bandgaps, where upper subcells have higher direct and/or indirect bandgaps than lower subcells, and the incorporation of heterojunctions with III-V semiconductor layers to reduce minority-carrier recombination and optimize current distribution, along with epitaxial growth and lattice-matched or metamorphic growth processes to enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lattice-matched subcells are stacked to increase output, then energy conversion efficiency is improved, but the number of subcells is restricted and parasitic losses increase
Solution Approach 1:
The patent divides the solar cell into multiple subcells with different bandgaps (e.g., GaInP, GaInAs, Ge subcells) that can be stacked to capture different portions of the solar spectrum. Each subcell is optimized for specific wavelength ranges, allowing the system to process broader energy distribution without excessive complexity in any single subcell.
Solution Approach 2:
The patent varies the energy bandgap parameter across different subcells to optimize performance. By selecting materials with progressively lower bandgaps (GaInP: 1.8-1.9 eV, GaInAs: 1.4-1.5 eV, Ge: 0.6-0.7 eV), the system efficiently converts different photon energy ranges while maintaining manageable complexity through parameter optimization rather than uniform design.
2Power
If high current densities are used to increase power output, then electrical power is improved, but series resistance losses increase and radiation resistance is impaired
Solution Approach 1:
The patent employs tunnel junctions with dynamically optimized doping concentrations (1×10^19 to 1×10^21 atoms/cm³) to maintain low resistance under varying current conditions. The tunnel junctions are designed with specific thicknesses (50-500 nm) and doping profiles that adapt to current density changes, reducing series resistance losses while maintaining high power output capability.
Solution Approach 2:
The patent introduces tunnel junctions as intermediary elements between subcells to facilitate efficient current transfer. These tunnel junctions act as low-resistance mediators that connect subcells operating at different current densities, reducing series resistance losses and enabling high power output without the harmful effects of direct high-current connections.
3Productivity
If more subcells are added to increase efficiency, then energy conversion is improved, but current matching requirements increase parasitic losses
Solution Approach 1:
The patent optimizes each subcell's local properties (bandgap, thickness, doping concentration) to match its specific function in the stack. The GaInP subcell is optimized for high-energy photons with specific thickness (1-5 μm), while the Ge subcell is optimized for low-energy photons with different parameters. This local optimization reduces parasitic losses from current matching by allowing each subcell to operate at its optimal point.
Solution Approach 2:
The patent uses composite material structures combining different semiconductor compounds (GaInP, GaInAs, Ge) with complementary properties. Each material contributes its optimal characteristics to the overall system, with the composite structure enabling efficient current matching across subcells through careful selection of material properties and interface design, thereby reducing parasitic losses.
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 significantly increases the efficiency of multijunction solar cells by allowing for more subcells with improved voltage and current output, reducing series resistance, and better utilization of excess photogenerated current, leading to higher 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
incorporation of heterojunctions with III-V semiconductor layers to reduce minority-carrier recombination
Implementation Method 3
epitaxial growth and lattice-matched or metamorphic growth processes
Data Source
AI summary
Device structures, apparatuses, and methods are disclosed for photovoltaic cells that may be a single-junction or multijunction solar cells, with at least a first layer comprising a group-IV semiconductor in which part of the cell comprises a second layer comprising a III-V semiconductor or group-IV semiconductor having a different composition than the group-IV semiconductor of the first layer, such that a heterostructure is formed between the first and second layers.