Multi-junction Solar Cells Using Wafer Bonding and Layer Transfer

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Solution Overview

Problem

The integration of non-lattice-matched materials in multi-junction solar cells is limited by crystal lattice-matching requirements, which restricts the number of subcells that can be integrated and affects the efficiency of solar energy collection.

Innovation Solution

Wafer bonding and layer transfer techniques enable the integration of III-V semiconductors and group IV materials into monolithic structures, allowing for the fabrication of multi-junction solar cells with non-lattice-matched materials, such as InGaAs, GaAs, AlGaAs, and Si, without the need for epitaxy, and the use of flexible substrates for high-performance solar cells.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If epitaxy is used to fabricate multi-junction solar cells, then series connected subcells can be formed, but the number of subcells that can be integrated is limited due to crystal lattice-matching requirements

Engineering Contradiction:

Improvenumber of subcells that can be integratedVSAvoidcrystal lattice-matching requirements

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The solar cell structure is divided into separate subcells that are independently fabricated on different substrates and then bonded together. This segmentation allows each subcell to be optimized for its specific material system without being constrained by lattice-matching requirements with other subcells, thereby enabling integration of more subcells with diverse band gaps.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A tunnel junction is introduced as an intermediary element between subcells to enable electrical connection. The tunnel junction serves as a mediator that allows current to pass between subcells with different materials and lattice structures, overcoming the limitation of direct epitaxial growth between mismatched materials.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If subcell band gaps are engineered for efficient solar spectrum collection, then high efficiency is achieved, but material integration limitations restrict the number of subcells

Engineering Contradiction:

Improveefficiency losses in single-junction cellsVSAvoidnumber of subcells that can be integrated

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The invention employs composite material structures where multiple semiconductor materials with different band gaps are integrated into a single device. By using bonding techniques rather than epitaxial growth, the patent combines materials like GaInP, GaAs, and Si that would be incompatible in a monolithic epitaxial structure, creating a composite multi-junction cell that captures broader solar spectrum.

Inventive Principle:

Principle #40Composite materials

3Reliability

If monolithic process is used with heavily doped tunnel junction, then electrical connection between subcells is achieved, but photo-current matching constraints limit design flexibility

Engineering Contradiction:

Improveelectrical connection between subcellsVSAvoiddesign flexibility of multi-junction structure

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The monolithic structure is segmented into separately fabricated subcells that are bonded together. This allows independent optimization of each subcell's photo-current characteristics before assembly, providing greater design flexibility while maintaining reliable electrical connections through the tunnel junction intermediary.

Inventive Principle:

Principle #1Segmentation

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 expands the possibilities for multi-junction solar cell designs, enhancing efficiency by integrating incompatible materials, reducing material costs, and improving mechanical and thermal properties, while allowing for flexible substrate use, thus overcoming the limitations of traditional epitaxy-based methods.

Implementation Method 1

Wafer bonding and layer transfer enables the integration of otherwise incompatible materials to form novel multi-junction solar cell structures

Methodology Applied

Scientific EffectWafer bonding: Welding

Implementation Method 2

Multi-junction solar cells consist of two or more p-n junction subcells with band gaps engineered to enable efficient collection of the broad solar spectrum

Methodology Applied

Scientific EffectPhotovoltaic effect: Photovoltaic Effect

Data Source

PatentUS7846759B2Multi-junction solar cells and methods of making same using layer transfer and bonding techniques

Publication Date: 2010.12.07 KONINKLIJKE PHILIPS NV

AI summary

A multi-junction solar cell includes an active silicon subcell, a first non-silicon subcell bonded to a first side of the active silicon subcell, and a second non-silicon subcell bonded to a second side of the active silicon subcell. This and other solar cells may be formed by bonding and layer transfer.