Multijunction Solar Cell Back Reflector With Diffusion Barrier
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Solution Overview
Problem
Inverted metamorphic multijunction solar cells face challenges in efficiency due to metal diffusion into active layers and limited optical path length, particularly in the composition and design of the back metal layer, which impairs performance and increases temperature.
Innovation Solution
A method of manufacturing solar cells involving the deposition of a reflective metal layer with high reflectivity, composed of metals like Al, Be, and Ni, and a contact metal layer of Ag, Au, and Ti, along with a diffusion barrier layer, to enhance reflectivity and reduce heat absorption, while maintaining the structural integrity of the solar cell layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional back metal layer is used in inverted metamorphic multijunction solar cells, then the electrical contact function is achieved, but metal diffusion into active layers occurs and efficiency is impaired
Solution Approach 1:
The back metal layer is segmented into multiple functional sub-layers: a reflective metal layer (Al, Be, or Ni) for optical reflection, a diffusion barrier layer for preventing metal migration, and a contact metal layer for electrical connection. This segmentation allows each layer to perform its specific function without interfering with others, resolving the contradiction between maintaining electrical contact and preventing efficiency degradation from metal diffusion.
Solution Approach 2:
A diffusion barrier layer is introduced as an intermediary between the reflective metal layer and the active semiconductor layers. This intermediary layer specifically prevents metal diffusion into the active layers while allowing the reflective layer to maintain its optical function and the contact layer to provide electrical connection, thus preserving efficiency without compromising electrical contact.
2Productivity
If the optical path length in the solar cell is increased through back reflection, then energy conversion efficiency is improved, but heat accumulation and temperature increase occur
Solution Approach 1:
The back metal layer is designed with local quality differentiation: the reflective metal layer (Al, Be, or Ni) provides high reflectivity (greater than 80% in the 850-2000 nm wavelength range) to increase optical path length and improve energy conversion efficiency, while the diffusion barrier layer and contact metal layer are positioned to manage thermal characteristics. This localized functional differentiation allows the cell to benefit from enhanced light reflection without excessive heat accumulation in the active regions.
3Productivity
If a reflective metal layer with high reflectivity is deposited, then infrared radiation is reflected and optical path length is increased, but metal diffusion into active layers is facilitated
Solution Approach 1:
The back metal structure is segmented into distinct layers with the reflective metal layer (Al, Be, or Ni) separated from the active semiconductor layers by a diffusion barrier layer. This segmentation allows the reflective layer to achieve high reflectivity for increased optical path length while the diffusion barrier layer prevents metal diffusion into the active layers, maintaining material stability.
Solution Approach 2:
A diffusion barrier layer is positioned as an intermediary between the reflective metal layer and the active semiconductor layers. This intermediary layer specifically addresses the metal diffusion problem while allowing the reflective layer to maintain its high reflectivity properties, thus enabling both increased optical path length and maintained material stability.
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 solution increases the solar cell's efficiency by reflecting infrared radiation back into the subcells, reducing operating temperature, and preventing metal diffusion into the active layers, thereby improving the overall performance and longevity of the solar cells.
Implementation Method 1
depositing a reflective metal layer composed of any one or more of the following metals or alloys thereof: Al, Be, and Ni to a thickness between 50 nm and 5 microns over said semiconductor contact layer such that the reflectivity of the reflective metal layer is greater than 80% in the wavelength range 850-2000 nm
Implementation Method 2
The higher conversion efficiency of III-V compound semiconductor solar cells compared to silicon solar cells is in part based on the ability to achieve spectral splitting of the incident radiation through the use of a plurality of photovoltaic regions with different band gap energies, and accumulating the current from each of the regions
Data Source
AI summary
A solar cell comprising an epitaxial sequence of layers of semiconductor material thrilling at least a first and second solar subcells; a semiconductor contact layer disposed on the bottom surface of the second solar subcell; a reflective metal layer disposed below the semiconductor contact layer such that the reflectivity of the reflective metal layer is greater than 80% in the wavelength range 850 to 2000 nm, for reflecting light back into the second solar subcell.