Solar Cell Textured Surface Dopant Diffusion and Etching

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Solution Overview

Problem

The existing manufacturing processes for solar cells with p- or n-type bases face issues such as contamination, non-uniform dopant concentration profiles, reduced yield due to breakage, and inefficient impurity gettering, particularly with the screen printing method for forming back surface field layers.

Innovation Solution

A method involving texturing of both surfaces, followed by diffusion of dopants to create doped layers, and subsequent etching to retain texture, which prevents parasitic doping and allows for two-sided diffusion of phosphorus for improved impurity gettering, eliminating the need for screen printing and reducing breakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If screen printing method is used to form BSF layer, then the BSF layer can be formed on the back side, but parasitic diffusion contaminates the front side causing non-uniform dopant concentration

Engineering Contradiction:

Improvedopant concentration uniformityVSAvoidparasitic diffusion contamination

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

A masking layer is introduced as an intermediary barrier between the dopant source on the back side and the front side of the substrate. This masking layer prevents parasitic diffusion of dopant to the front side during the diffusion process, thereby eliminating contamination while still allowing the BSF layer to be formed on the back side.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The diffusion process is segmented into controlled stages: first forming the BSF layer on the back side with masking protection, then removing the masking layer, and finally forming the emitter layer on the front side. This segmentation prevents simultaneous exposure of both sides to dopant, eliminating parasitic diffusion.

Inventive Principle:

Principle #1Segmentation

2Productivity

If screen printing is used to form BSF layer, then the layer can be created, but substrate breakage increases reducing manufacturing yield

Engineering Contradiction:

Improvemanufacturing yieldVSAvoidsubstrate integrity

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The mechanical screen printing process is replaced with a chemical diffusion process. Instead of physically printing paste onto the substrate using screen printing equipment, the dopant is introduced through chemical diffusion from a solid source on the back side, eliminating the mechanical stresses that cause substrate breakage.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If one-sided diffusion is used for n-type BSF layer, then the process is simpler, but impurity gettering efficiency is reduced

Engineering Contradiction:

Improveimpurity gettering efficiencyVSAvoiddiffusion process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The diffusion process is extended from one-sided to two-sided diffusion by introducing dopant sources on both the front and back sides of the substrate. This creates a three-dimensional dopant distribution pattern that enhances impurity gettering throughout the substrate volume, rather than only at the back surface.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 enhances manufacturing consistency, reduces yield loss, and improves solar cell efficiency through better surface passivation and impurity removal.

Implementation Method 1

texturing the front surface to create a textured front surface

Methodology Applied

Scientific EffectLight scattering: Scattering

Implementation Method 2

creating by diffusion of a dopant of the first conductivity type a first conductivity-type doped layer in the textured front surface and a back surface field layer of the first conductivity type in the back surface

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 3

removing the first conductivity-type doped layer from the textured front surface by an etching process adapted for retaining texture of the textured front surface

Methodology Applied

Scientific EffectChemical etching:

Implementation Method 4

two-sided diffusion of phosphorus in both front and back surfaces allows an improved gettering of impurities from the silicon substrate

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS9034670B2Solar cell and method for manufacturing such a solar cell

Publication Date: 2015.05.19 NEDERLANDSE ORG VOOR TOEGEPAST NATUURWETENSCHAPPELIJK ONDERZOEK TNO

AI summary

A method (100; 100a; 100b; 100c) for manufacturing a solar cell from a semiconductor substrate (1) of a first conductivity type, the semiconductor substrate having a front surface (2) and a back surface (3). The method includes in a sequence: texturing (102) the front surface to create a textured front surface (2a); creating (103) by diffusion of a dopant of the first conductivity type a first conductivity-type doped layer (2c) in the textured front surface and a back surface field layer (4) of the first conductivity type in the back surface; removing (105; 104a) the first conductivity-type doped layer from the textured front surface by an etching process adapted for retaining texture of the textured front surface; creating (106) a layer of a second conductivity type (6) on the textured front surface by diffusion of a dopant of the second conductivity type into the textured front surface.