Si/Ge Tandem Solar Cell Substrate Transfer via Ion Implantation
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Solution Overview
Problem
The high cost and scarcity of single-crystal germanium substrates, along with the difficulty in epitaxially growing silicon on germanium due to temperature constraints, complicate the manufacturing of tandem-type photoelectric conversion elements with Si/Ge-based structures, leading to cumbersome and costly processes.
Innovation Solution
A method involving the formation of a hydrogen ion-implanted layer and surface activation treatment to bond a germanium-based crystal layer with a supporting substrate, allowing for the growth and lamination of silicon and germanium crystals at low temperatures, eliminating the need for high-temperature treatments and costly substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-crystal germanium substrate is used, then the photoelectric conversion efficiency is improved, but the manufacturing cost increases and substrate availability decreases
Solution Approach 1:
The patent replaces expensive single-crystal germanium substrates with inexpensive silicon substrates. The silicon substrate serves as a temporary support during the epitaxial growth process, allowing the formation of high-quality germanium and silicon-germanium layers without requiring a costly germanium substrate. This substitution dramatically reduces manufacturing cost while maintaining the ability to produce efficient tandem solar cells.
Solution Approach 2:
The patent introduces a silicon-germanium mixed crystal layer as an intermediary between the silicon substrate and the top germanium-based crystal cell. This intermediate layer facilitates the epitaxial growth process by providing a transition structure that manages lattice mismatch and enables the formation of high-quality crystalline layers on the silicon substrate, thereby achieving efficient photoelectric conversion without using expensive germanium substrates.
2Adaptability or versatility
If silicon is epitaxially grown on germanium, then the tandem structure is formed, but the process complexity increases due to temperature constraints
Solution Approach 1:
The patent inverts the conventional growth sequence by first forming the germanium-based crystal cell on the silicon substrate through epitaxial growth, and then forming the silicon-based crystal cell on top of the germanium layer. This reversed approach allows the use of standard silicon epitaxial growth temperatures without risking germanium melting, thereby simplifying the manufacturing process while still achieving the desired tandem structure.
Solution Approach 2:
The patent utilizes precise control of epitaxial growth parameters, including temperature, pressure, and gas composition, to enable the growth of high-quality germanium and silicon-germanium layers on silicon substrates. By optimizing these parameters, the process achieves the necessary crystal quality for efficient photoelectric conversion without requiring excessively complex process conditions.
3Manufacturing precision
If high-temperature epitaxial growth is used, then the silicon layer quality is improved, but the germanium substrate melts
Solution Approach 1:
The patent performs preliminary formation of the germanium-based crystal cell with controlled thickness and structure before growing the silicon layer. This preliminary action allows optimization of the germanium layer properties to withstand subsequent processing steps. Additionally, the use of silicon-germanium mixed crystal layers as intermediate structures prepares the system for low-temperature silicon epitaxial growth, preventing germanium melting while maintaining silicon layer quality.
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 method enables the cost-effective production of tandem-type photoelectric conversion elements with Si/Ge-based structures without requiring expensive germanium substrates, maintaining crystal quality and reducing manufacturing complexity.
Implementation Method 1
a second step of forming a hydrogen ion-implanted layer by implanting ions into a silicon crystal region having the first conductivity type through the silicon layer having the second conductivity type
Implementation Method 2
a third step of vapor-phase growing a germanium-based crystal layer on the silicon layer having the second conductivity type by successively laminating germanium crystals or silicon-germanium mixed crystals
Implementation Method 3
a fourth step of applying a surface activation treatment to at least one of the surface of a supporting substrate and the surface of the germanium-based crystal layer; a fifth step of bonding together the surface of the germanium-based crystal layer and the surface of the supporting substrate
Data Source
Figure 1
Figure 2(A)~2(D)
Figure 3(A)~3(C)
AI summary
A silicon layer (10B) having a conductivity type opposite to that of a bulk is provided on the surface of a silicon substrate (100) and hydrogen ions are implanted to a predetermined depth (L) into the surface region of the silicon substrate (100) through the silicon layer (10B) to form a hydrogen ion-implanted layer (11). Then, an n-type germanium-based crystal layer (20A) whose conductivity type is opposite to that of the silicon layer (10B) and a p-type germanium-based crystal layer (20B) whose conductivity type is opposite to that of the germanium-based crystal layer (20A) are successively vapor-phase grown to provide a germanium-based crystal (20). The surface of the germanium-based crystal layer (20B) and the surface of the supporting substrate (30) are bonded together. In this state, impact is applied externally to separate a silicon crystal (10) from the silicon substrate (100) along the hydrogen ion-implanted layer (11), thereby transferring (peeling off) a laminated structure composed of the germanium-based crystal (20) and the silicon crystal (10) onto the supporting substrate (30).