Tandem Solar Cell Structure Using Resonant Tunneling Interfaces
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Solution Overview
Problem
Conventional tandem solar cells using Ge and GaAs substrates are limited by high material costs and inefficiencies in harnessing photons with energies above 2.2 eV due to band offset voltage-based losses and lattice mismatch issues.
Innovation Solution
The integration of resonant tunneling structures (RTS) and novel dislocation reduction techniques on Si substrates, combined with II-VI semiconductors like ZnSSe and ZnMgSSe, to create high-efficiency tandem solar cells that efficiently harness photons across a wider energy range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional Ge and GaAs substrates are used for tandem solar cells, then high efficiency in harnessing solar energy is achieved, but material cost increases and lattice mismatch issues occur
Solution Approach 1:
The patent replaces expensive Ge and GaAs substrates with inexpensive Si substrates for growing II-VI semiconductor layers. This substitution dramatically reduces material cost while maintaining the ability to achieve high efficiency through the tandem cell structure and resonant tunneling interfaces, effectively using cheaper materials to accomplish the same function.
Solution Approach 2:
The patent changes the material system from III-V (Ge/GaAs/GaInP) to II-VI (ZnSSe/ZnMgSSe) semiconductors grown on Si substrates. This parameter change in material composition and crystal structure enables compatibility with low-cost Si while achieving the desired optical and electrical properties for high efficiency solar energy conversion.
2Productivity
If conventional tunnel junctions are used to integrate tandem cells, then cell integration is achieved, but band offset voltage losses occur reducing efficiency
Solution Approach 1:
The patent introduces resonant tunneling structures as intermediary layers at the interfaces between tandem cell sub-cells. These RTS layers act as mediators that enable efficient carrier transport across heterojunctions with large band offsets, reducing voltage losses while maintaining proper electrical integration of the multi-junction structure.
Solution Approach 2:
The patent employs composite material structures combining II-VI semiconductors (ZnSSe, ZnMgSSe) with carefully engineered tunnel junction and resonant tunneling structure layers. This composite approach creates optimized interfaces that minimize band offset voltage losses while maintaining the benefits of multi-junction tandem cell integration.
3Ease of manufacture
If Si substrates are used for growing Ge epitaxial layers, then material cost is reduced, but dislocation densities increase due to lattice mismatch
Solution Approach 1:
The patent applies local quality by using Si substrates specifically for growing II-VI semiconductor layers where the lattice mismatch is manageable, rather than attempting to grow all cell components directly on Si. The localized use of Si substrates with appropriate buffer and transition layers minimizes dislocation propagation while maintaining cost advantages.
Solution Approach 2:
The patent accepts and manages the presence of dislocations by using Si substrates as a disposable, low-cost foundation that is eventually superseded by higher-quality epitaxial layers. The Si substrate serves its purpose as an inexpensive starting point that can be overcome through advanced epitaxial growth techniques.
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 enhances solar cell efficiency by reducing band offset voltage drops and dislocation densities, enabling effective energy conversion from 2.2 eV to 3.7 eV, surpassing conventional Ge/GaAs/GaInP-based cells.
Implementation Method 1
the resonant tunneling structure is configured to facilitate current flow between semiconducting layers belonging to two different solar cells having different energy gaps
Implementation Method 2
tandem cells efficiently harness solar energy and reduce excess energy losses by absorbing different energy photons in semiconductor layers having different energy gaps
Data Source
AI summary
Solar cell structures comprising a plurality of solar cells, wherein each solar cell is separated from adjacent solar cell via a tunnel junction and/or a resonant tunneling structure (RTS), are described. Solar cells are implemented on Ge, Si, GaN, sapphire, and glass substrates. Each of the plurality of solar cells is at least partially constructed from a cell material which harnesses photons having energies in a predetermined energy range. In one embodiment each solar cell comprises of at least two sub-cells. It also describes a nano-patterned region/layer to implement high efficiency tandem/multi-junction solar cells that reduces dislocation density due to mismatch in lattice constants in the case of single crystalline and/or polycrystalline solar cells. Finally, solar structure could be used as light-emitting diodes when biased in forward biasing mode. The mode of operation could be determined by a programmed microprocessor.