Solar Cell Back Surface Field Width and Emitter Conductivity

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Solution Overview

Problem

Conventional back contact solar cells face efficiency losses due to narrow base regions on the back surface, which increase processing costs and require strict manufacturing tolerances, while also complicating electrode designs.

Innovation Solution

The use of wider back surface field regions, exceeding 0.6 millimeters, combined with a front floating emitter layer having an average electrical conductivity value calculated as C = a*W - b, where W is the width of the back surface field region, allows for efficient lateral transport of minority charge carriers without significant efficiency loss, where a = 5.54 milliSiemens square/millimeter and b = 1.0 milliSiemens square.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If narrow base regions are used on the back surface, then electrical shading losses are reduced and efficiency is improved, but processing costs increase and manufacturing tolerances become stricter

Engineering Contradiction:

Improveelectrical shading lossVSAvoidprocessing cost

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The patent changes the geometric parameter of base region width from narrow (conventional) to wide (greater than 0.6mm), and compensates for the resulting electrical shading loss by adjusting the electrical conductivity parameter of the front floating emitter layer. This parameter substitution allows wider base regions to be used without significant efficiency penalty, thereby simplifying manufacturing processes and reducing processing costs.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If narrow base regions are used on the back surface, then electrical shading losses are reduced and efficiency is improved, but manufacturing tolerances become stricter

Engineering Contradiction:

Improveelectrical shading lossVSAvoidmanufacturing tolerance

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent relaxes the manufacturing tolerance requirement by changing the base region width parameter from narrow to wide (greater than 0.6mm). The potential efficiency loss from increased electrical shading is compensated by adjusting the front floating emitter layer's electrical conductivity, thereby achieving easier manufacturing with standard tolerances while maintaining acceptable efficiency.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If wider back surface field regions are used, then manufacturing is simplified and costs are reduced, but efficiency loss occurs due to increased electrical shading

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidefficiency loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent achieves wider back surface field regions (greater than 0.6mm) by adjusting the electrical conductivity parameter of the front floating emitter layer. This parameter adjustment compensates for the increased electrical shading effect, allowing wider base regions to be used without substantial efficiency loss while enjoying the manufacturing simplicity and cost benefits.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies different electrical conductivity characteristics to different regions of the front floating emitter layer. By optimizing the conductivity distribution locally above the wider base regions, the patent compensates for electrical shading losses in those specific areas while maintaining good passivation properties in other regions, thereby enabling wider base regions without substantial overall efficiency loss.

Inventive Principle:

Principle #3Local 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 approach enables the use of wider back surface field regions without substantial efficiency loss, simplifying manufacturing and reducing costs by allowing for equal width conductor tracks and optimized emitter widths, thereby enhancing overall solar cell efficiency.

Implementation Method 1

The front floating emitter (FFE) provides for passivation by reducing the product of the densities of positive and negative mobile charge carriers at the surface, so that contributions to the recombination rates that depend on that product are reduced.

Methodology Applied

Scientific EffectCharge carrier density reduction:

Implementation Method 2

a front floating emitter layer having an average electrical conductivity value calculated as C = a*W - b, where W is the width of the back surface field region, allows for efficient lateral transport of minority charge carriers

Methodology Applied

Scientific EffectLateral charge carrier transport: Conduction (electrical)

Data Source

PatentEP2962335B1Photo-voltaic cell and method of manufacturing such a cell

Publication Date: 2021.04.28 STICHTING ENERGIEONDERZOEK CENT NEDERLAND

Figure 1a
Figure 1b
Figure 2~3

AI summary

A photo-voltaic cell, comprising a semi-conductor substrate, having a front surface and a back surface. Back surface field regions and emitter regions for collecting photo-current are provided, located alternatingly at the back surface of the substrate, at least one of the back surface field regions having a width of more than six hundred micrometer. A front floating emitter layer is provided at the front surface at least above said one of the back surface field regions, wherein the front floating emitter layer has an average electrical conductivity selected dependent on the width of said one of the back surface field regions.