III-V Bonding Layers for Multijunction Photovoltaic Cells
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Solution Overview
Problem
Conventional multijunction photovoltaic cells face efficiency limitations due to lattice mismatch between subcells, restricting the selection of semiconductor materials and causing mechanical strain and defects, while existing bonding techniques, such as metallic and insulating layers, either hinder electrical conduction or obstruct light transmission.
Innovation Solution
The method involves forming bonding layers of III-V materials, specifically indium phosphide and gallium arsenide or gallium indium phosphide, doped with selenium or tellurium, to reduce the absorption edge wavelength and achieve low surface roughness, allowing for direct bonding of subcells without obstructing light transmission and enabling efficient electrical conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional bonding techniques (metallic or insulating layers) are used to bond subcells, then mechanical bonding is achieved, but electrical conduction is hindered or light transmission is obstructed
Solution Approach 1:
The bonding layer material composition is changed from conventional metallic or insulating materials to III-V semiconductor materials with specific band gap energies. By controlling the band gap energy parameter of the bonding layer material, both mechanical bonding strength and electrical conduction are maintained, resolving the contradiction between strong bonding and electrical functionality.
Solution Approach 2:
The bonding layer is formed as a composite structure with specific III-V semiconductor materials that combine mechanical bonding properties with electrical conduction capabilities. This composite approach allows the bonding layer to simultaneously provide both mechanical strength and electrical functionality, overcoming the limitations of single-material bonding layers.
2Illumination intensity
If subcells are bonded directly without intermediate layers, then light transmission is maximized, but lattice mismatch causes mechanical strain and defects
Solution Approach 1:
A bonding layer made of III-V semiconductor material is introduced as an intermediary between subcells with different lattice constants. This intermediary layer accommodates lattice mismatch through its own crystal structure, reducing mechanical strain and preventing defects while maintaining optical transparency, thus resolving the contradiction between direct bonding and mechanical stability.
3Strength
If bonding layers with high absorption edge wavelength are used, then mechanical bonding is achieved, but light transmission in the visible spectrum is reduced
Solution Approach 1:
The band gap energy parameter of the bonding layer material is optimized to have a higher energy (shorter wavelength) absorption edge than the visible spectrum. This parameter change ensures that the bonding layer absorbs UV and blue light for mechanical bonding while remaining transparent to green, yellow, and red light, thus maintaining high light transmission in the visible range.
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 the efficiency of multijunction photovoltaic cells by reducing mechanical strain, expanding material selection, and improving light transmission and electrical conduction, leading to better solar energy utilization and higher operational efficiency.
Implementation Method 1
The bonding layers are doped with a group VI element dopant in order to reduce the absorption edge wavelength of the bonding layers
Implementation Method 2
One method to collect and utilize solar energy is through photovoltaic (PV) cells, which convert solar energy directly into electrical energy. The conversion of energy can be provided by pn-junction diodes fabricated from n-type and p-type conductive regions in semiconductor materials.
Data Source
Figure 1~2
Figure 3~4
AI summary
A method of fabricating a semiconductor structure includes the formation of a first bonding layer at least substantially comprised of a first III-V material on major a surface of a first element, and formation of a second bonding layer at least substantially comprised of a second III-V material on a major surface of a second element. The first bonding layer and the second bonding layer are disposed between the first element and the second element, and the first element and the second element are attached to one another at a bonding interface disposed between the first bonding layer and the second bonding layer. Semiconductor structures are fabricated using such methods.