Complete Report - University of New South Wales

The SiN fi lms with nr = 2.35 were annealed at 450°C in an N2 ambient for a total duration of
240 minutes. The evolution in implied open-circuit voltage of the annealed samples is plotted
in Figure 4.3.2.13b. After 5 minutes of annealing, the relationship between the implied Voc
and sheet resistance of boron emitter resembles that of as-deposited condition. However,
after 30 minutes of annealing, the relationship has changed, with the implied open-circuit
voltage increasing with increasing boron emitter sheet resistance. It is likely that the implied
open-circuit voltage at low sheet resistance range is limited by the emitter recombination,
whereas, at the high sheet resistance range, the surface recombination dominates. After
240 minutes of annealing, an implied open-circuit voltage of 683 and 718 mV on 135 and 215
ohm/sq boron emitter respectively was achieved. Dark emitter saturation current densities
as low as 5 fA/cm2 per side was achieved by fully annealing the SiN fi lms. The results also
indicate that the passivation quality provided by the annealed fi lms is superior to that by oxide
for sheet resistance above around 100 ohm/sq.
Figure 4.3.2.13: (a) The implied open-circuit voltage of various SiN fi lms at as-deposited
condition on boron emitters across range of sheet resistances; (b) the implied open-circuit
voltage of the nr = 2.35 SiN fi lm after various annealing times; (c) the extracted emitter
saturation current density of the fully annealed nr = 2.35 SiN fi lms.
4.3.2.3. PHOTOLUMINESCENCE AND PHOTOCONDUCTANCE TECHNIQUES FOR
SILICON SOLAR CELL CHARACTERIZATION AND DEVELOPMENT
Photoluminescence Techniques
Photoluminescence characterization techniques have recently emerged in other Centre
work as an accurate, fast, powerful tool for developing high-effi ciency silicon solar cells.
The related PL techniques – spatially averaged PL lifetime, Suns-PL and PL imaging – offer
unprecedented quality and quantity of information that is benefi cial for a wide spectrum
of solar cell development and fabrication purposes. As PL techniques are fast (especially
imaging), contact-less and provide complementary spatial and injection level dependent
information about recombination, they are very powerful techniques relevant to both well
controlled laboratories and high-throughput solar cell factories.
In 2005, we demonstrated the application of multiple PL techniques to several important
aspects of high-effi ciency solar cell development at UNSW: wafer handling, furnace
contamination, process-induced defects, cell design and cell process monitoring. In only a few
months, photoluminescence (PL) techniques have greatly enhanced our solar cell fabrication
sequences and designs, identifying problems that, in some cases, existed in our fabrication
sequences for over ten years. With measurement times of 1 second per wafer (regardless
of area) the power of this technique is as relevant to high-throughput mass-production as it is
to laboratory cell research and development.
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