Solar Cell Back-Surface Electrode Crack Prevention

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Solution Overview

Problem

PERC type solar cell elements face issues with crack formation in the back-surface electrode due to thermal stress caused by differences in thermal expansion coefficients between the protective layer and the metal electrode, leading to increased electrical resistance and reduced power generation efficiency.

Innovation Solution

A solar cell element design featuring a protective layer with a thickness variation region that increases in thickness away from the inner edge of the hole portion, and a back-surface electrode that decreases in thickness, reducing thermal stress and crack formation by gradual heat shrinkage during firing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a protective layer is formed on the passivation layer to protect the semiconductor substrate, then the reliability of the solar cell element is improved, but thermal stress causes crack formation in the back-surface electrode leading to increased electrical resistance

Engineering Contradiction:

Improveprotection of semiconductor substrateVSAvoidthermal stress and crack formation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The protective layer is designed with spatially varying thickness: a first region with greater thickness located at a distance from the inner edge portion of the hole portion, and a second region with smaller thickness surrounding the first region. This local quality variation reduces thermal stress concentration and prevents crack formation in the back-surface electrode during firing, while maintaining the protective function of the layer.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If the protective layer has uniform thickness to simplify manufacturing, then the ease of manufacture is improved, but thermal stress concentration occurs leading to crack formation and reduced power generation efficiency

Engineering Contradiction:

Improveuniform thickness formationVSAvoidcrack-free electrode formation

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The thickness parameter of the protective layer is changed spatially to resolve the contradiction. By making the thickness non-uniform (greater in the first region away from the hole portion inner edge, smaller in the surrounding second region), the design prevents thermal stress concentration and crack formation during firing, thereby achieving both manufacturing feasibility and high precision electrode formation without cracks.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If the back-surface electrode has constant thickness to simplify the structure, then the device complexity is reduced, but thermal expansion differences cause stress concentration and crack formation

Engineering Contradiction:

Improveelectrode structure simplicityVSAvoidelectrode integrity under thermal stress

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The back-surface electrode is designed with spatially varying thickness: a first region with greater thickness located at a distance from the inner edge portion of the hole portion, and a second region with smaller thickness surrounding the first region. This local quality variation reduces thermal stress concentration and prevents crack formation in the back-surface electrode during firing, while maintaining the protective function of the layer.

Inventive Principle:

Principle #3Local quality

4Reliability

If the protective layer thickness increases away from the hole portion inner edge to reduce thermal stress, then crack formation is reduced, but the device complexity increases

Engineering Contradiction:

Improvecrack-free electrodeVSAvoidthickness variation structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

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

This design reduces the likelihood of crack formation and improves power generation efficiency by minimizing electrical resistance and maintaining the integrity of the back-surface electrode.

Implementation Method 1

differences in thermal expansion coefficients between the protective layer and the metal electrode, leading to increased electrical resistance and reduced power generation efficiency

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

thermal stress caused by differences in thermal expansion coefficients between the protective layer and the metal electrode

Methodology Applied

Scientific EffectThermal stress: Thermal Expansion

Data Source

PatentUS10749047B2Solar cell element and method for manufacturing solar cell element

Publication Date: 2020.08.18 KYOCERA CORP

AI summary

The solar cell element includes a semiconductor substrate with first and second surfaces, a passivation layer located on the second surface, a protective layer located on the passivation layer, and a back-surface electrode located on the protective layer. The back-surface electrode is electrically connected to the semiconductor substrate via one or more hole portions penetrating the protective layer and the passivation layer. The protective layer includes a first region showing a tendency to increase in thickness as a distance from an inner edge portion of the hole portion and a second region surrounding the first region. A distance between a position of the first region farthest from the inner edge portion and the inner edge portion is larger than a thickness in the second region. The back-surface electrode shows a tendency to decrease in thickness on the first region as a distance from the inner edge portion.