Complete Report - University of New South Wales

Voc, mV
705
703
701
699
697
695
693
691
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
0 5 10
One - sun Illumination Time, hr
Jsc, ma/cm2
40.0
39.8
39.6
39.4
39.2
39.0
38.8
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
38.6
0 5 10
One - sun Illumination Time, hr
FF, %
80.0
79.5
79.0
78.5
78.0
77.5
77.0
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
Efficiency, %
22.5
22.0
21.5
21.0
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
76.5
0 5 10
One -sun Illumination Time, hr
20.5
0 5 10
One -sun Illumination Time, hr
Figure 4.3.1.6: The performance of rear boron emitter n-type PERT cells during 1–2 days
one-sun illumination by ELH lamp. The edge recombination may have been reduced by the
illumination process.
For the cells in the fi rst batch, Wnrj1, with scribed and cleaved through emitter edges,
effi ciencies improved by 0.2% to 0.4% absolute after illumination. Most of these gains
came from Jsc improvements, which is a sign of reduced total recombination loss. The high
recombination at the scribed edges may have been reduced during illumination, possibly due
to slight oxidation of the cleaved edge surfaces.
However, the cells in the latest batch, Wnrj7, did not show this increase to the same extent
under one-sun illumination. Separating the emitter from the cleaved exposed edges with the
limited-area emitter design has stabilised cell performance, as well as improving the cell fi ll
factors. Fortunately, cleaved emitter edges for larger area commercial cells will have much
less effect on the fi nal cell performance.
It is clear that moving the light sensitive boron diffused emitter from the front to the rear
surface has signifi cantly improved the cell stability.
4.3.1.6 Recent Design Without Cell Scribing
Recently, the n-type re-PERT cells have been redesigned into one cell on a single wafer
structure. This will eliminate the need for cell scribing. In this case, the edge recombination
loss from the scribed and the cleaved edge surfaces will be eliminated. This structure is
designed to test the recombination contribution from the scribed edges. It will also allow
investigation of the full potential of such n-type re-PERT cell structures. We are confi dent that
such device structures with minimum edge recombination contribution will further improve
the cell effi ciency to a new level above the present world record, as demonstrated by the
scribed re-PERT cells.
30