A CostEffective Process for HighQuality Back Surface Passivation in Si Solar Cells

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A Cost-Effective Process for High-Quality Back
Surface Passivation in Si Solar Cells
Proposal

• Vichai Meemongkolkiat
• November 13, 2003

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Outline

• Objective
• Motivation
• Introduction
• Procedure
• Facilities requirements
• Timetable
• Work plan

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Objective

• To find a cheap and fast way to passivate the
  back surface of solar cells

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Motivation

• For solar cells to be able to compete with other
  electricity sources, /Watt needs to be reduced
• Improve efficiency
• Reduce production cost
• For high-efficiency cells, good back surface
  passivation is mandatory

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Introduction
Bulk
Emitter
Front
Back
p
n

• Surface recombination velocity (SRV) is the
  figure of merit for passivation quality
• Lower is better
• Below 200 cm/s is decent

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Procedure 4 Steps
Choose the basic passivation methods
Achieve decent quality of passivation on each of
the chosen methods
Apply the methods on actual solar cells
Assess SRV
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Choose the Basic Passivation Methods
Step 1

• Three basic methods for passivation were chosen

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Achieve Decent Quality of Passivation on Each of
the Chosen Methods
Step 2

• Al-BSF
• Method for uniform Al-BSF was established
• SRV of 230 cm/s was obtained
• Dielectric passivation
• RTO/LF-SiNx provided the best passivation
• SRV of 51 cm/s was obtained by RTO/LF-SiNx
• (without electrical contacts)
• Boron-BSF
• Results indicated promisingly low SRV

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Apply the Methods on Actual Solar Cells
Step 3

• Three solar cells structures were proposed

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Step 4
Assess SRV
SRV of the back surface
Bulk lifetime
Long-wavelength internal quantum efficiency (IQE)

• SRV can be obtained by measuring IQE and bulk
  lifetime

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Facilities Requirements

• Characterization tools
• SEM
• IQE system
• PCD tool
• PC1D simulation program

• Fabrication tools
• Diffusion furnace
• PECVD
• RTP
• Screen-printer
• Belt furnace

• Resources
• FZ wafers, boron-BSF sample, and screen-printing
  pastes

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Timetable
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Work Plan

• Completed tasks
• Chose the three basic passivation methods
• Designed the three solar cells structures
• Fabricated solar cells with Al-BSF structure and
  acquired the SRV
• Decided the type of dielectric to be used
• Acquired promisingly low SRV using boron-BSF
• Remaining tasks
• Establish the fabrication processes for the two
  remaining structures
• Fabricate and characterize the remaining
  structures to obtain SRV
• Compare all the structures in terms of electrical
  quality and cost-effectiveness

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Questions?