Conductive Adhesive Layer for Solar Cell Thermal Expansion Management

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Solution Overview

Problem

Existing solar cell structures face limitations in voltage and current output due to material mismatch in thermal expansion coefficients, particularly between silicon carriers and Group III-V solar cells, which restricts the use of metal-to-metal bonds to small devices, necessitating an improved connecting method for larger solar cells.

Innovation Solution

A solar cell structure featuring a carrier with a P-N junction adhesively bonded to a solar cell using an adhesive layer with conductive particles, which electrically couples the carrier to the solar cell, managing thermal expansion differences and enabling larger device bonding without additional conductive particles for electrical paths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If metal-to-metal bonding is used to connect the carrier to the solar cell, then electrical coupling is achieved, but the significant CTE mismatch (metal layer CTE: 10-20, GaAs CTE: 5.5, silicon CTE: 2.5) causes thermal expansion issues that limit the bonding to small devices only

Engineering Contradiction:

Improveelectrical coupling reliabilityVSAvoiddevice size applicability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent introduces an adhesive layer as an intermediary material between the metal interconnect and the solar cell. This adhesive layer has a CTE that is substantially matched to the solar cell material (within ±50%), serving as a buffer that absorbs thermal expansion differences. The adhesive layer bonds both the metal interconnect and solar cell together while accommodating thermal stress, enabling reliable electrical coupling for larger solar cell devices without the thermal expansion problems that limited metal-to-metal bonding to small devices only.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If an adhesive layer with conductive particles is used to bond the carrier to the solar cell, then thermal expansion mismatch is managed and larger devices can be bonded, but additional conductive particles are needed to establish electrical paths

Engineering Contradiction:

Improvedevice size applicabilityVSAvoidconductive particle concentration

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent merges multiple functions into the adhesive layer: it provides mechanical bonding between the metal interconnect and solar cell, manages thermal expansion mismatch through CTE matching, and establishes electrical conductivity through embedded conductive particles. By combining bonding, thermal management, and electrical conduction functions into a single layer, the design eliminates the need for separate conductive pathways, reducing overall device complexity while enabling larger solar cell applications.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If multiple conductive particles are added to create electrical paths in the adhesive layer, then electrical coupling is improved, but assembly costs and lateral conduction risks increase

Engineering Contradiction:

Improveelectrical coupling reliabilityVSAvoidassembly cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent optimizes the concentration and distribution parameters of conductive particles within the adhesive layer. By carefully controlling the particle concentration to be sufficient for electrical coupling but not excessive, the design achieves reliable electrical conductivity while minimizing material costs and manufacturing complexity. The particles are distributed to provide vertical conduction paths between the metal interconnect and solar cell contact regions, with concentration optimized to prevent lateral conduction that would cause electrical interference between adjacent cells, thereby reducing assembly costs while maintaining reliability.

Inventive Principle:

Principle #35Parameter changes

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 adhesive layer with conductive particles effectively addresses thermal expansion issues, allowing for the assembly of larger solar cells while maintaining low particle concentration to prevent lateral conduction, reducing assembly costs and interconnects, and providing efficient electrical coupling.

Implementation Method 1

an adhesive layer bonds the front side of the carrier to the solar cell

Methodology Applied

Scientific EffectAdhesive bonding: Adhesive

Implementation Method 2

the metal-to-metal layers used to connect the carrier to the solar cell include a coefficient of thermal expansion (CTE) that is significantly higher than the CTE of GaAs or silicon

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

The adhesive layer includes conductive particles that electrically couple the carrier to the solar cell

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS11581446B2Semiconductor device including an electrically conductive adhesive layer and a bypass diode in a carrier

Publication Date: 2023.02.14 THE BOEING CO

AI summary

A solar cell structure is disclosed. The solar cell structure comprises a carrier having a front side and a P-N junction, a solar cell electrically coupled to the front side of the carrier, and an adhesive layer. The adhesive layer bonds the front side of the carrier to the solar cell. The adhesive layer includes conductive particles that electrically couple the carrier to the solar cell.