Complete Report - University of New South Wales
Complete Report - University of New South Wales
Complete Report - University of New South Wales
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4.3 FIRST GENERATION: WAFER-BASED PROJECTS<br />
4.3.1 High Efficiency Cells<br />
<strong>University</strong> Staff:<br />
A/Pr<strong>of</strong>. Jianhua Zhao (group leader)<br />
Pr<strong>of</strong>. Martin Green<br />
Pr<strong>of</strong>. Stuart Wenham<br />
Research Fellows: Dr. Aihua Wang<br />
Research Assistant: Guangchun Zhang<br />
Technical Staff: Jules Yang<br />
During 2005, a cell effi ciency equalling the world record for n-type silicon cells has been<br />
demonstrated by a new rear emitter PERT cell structure, which was developed by the high<br />
effi ciency group at the Centre. The previous record was set more than a decade ago by<br />
Stanford <strong>University</strong>. This new cell structure is expected to produce further improvements<br />
in cell effi ciency and, importantly, is also suitable for low cost CZ silicon substrates. This<br />
research work is reported below.<br />
4.3.1.1 Rear Emitter PERT Cell Structure on N-type Silicon Substrates<br />
In 2004, a new rear-boron-emitter PERT (passivated emitter, rear totally-diffused) cell<br />
structure on n-type silicon substrates was developed by the high effi ciency cell group in the<br />
Centre. During the initial experiments, these devices demonstrated high cell effi ciencies<br />
close to 22%, and very stable cell performance under one-sun illumination and after long<br />
term storage in nitrogen. Figure 4.3.1.1 shows the structure <strong>of</strong> these n-type rear emitter<br />
PERT (re-PERT) cells.<br />
finger<br />
“inverted” pyramids<br />
Figure 4.3.1.1<br />
Rear boron emitter PERT cell<br />
structure on n-type silicon<br />
substrates<br />
double layer<br />
antireflection<br />
coating<br />
n-silicon<br />
rear contact<br />
oxide<br />
High effi ciency processing methods, similar to those used for PERL (passivated emitter, rear<br />
locally-diffused) cells, are used for processing these n-type re-PERT cells. These processing<br />
methods include lithographically defi ned regular inverted pyramids surface for excellent light<br />
trapping, TCA thermal oxide growth and aluminium anneal for high quality surface passivation,<br />
boron tribromide liquid source boron diffusion producing very low surface damage, lift-<strong>of</strong>f metal<br />
scheme combined with electro-chemical silver plating for minimum contact recombination<br />
and very little metal shading and resistance loss, and double layer antirefl ection coatings to<br />
further minimise the surface refl ection loss.<br />
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