Complete Report - University of New South Wales

The main Raman peak at 520 cm -1 broadens in damaged and disordered crystalline silicon
due to relaxation of the momentum conservation in the Raman scattering process. Hence, the
full width at half maximum (FWHM) of the main Raman peak at around 520 cm -1 is a quantity
that measures the amount of crystal disorder in our poly-Si fi lms. Raman measurements
were performed with a red laser (λ = 633 nm) on samples SPE-A and SPC. As a reference,
a polished Si wafer was also analysed. The Raman peak at ~ 520 cm -1 was fi tted with a
mixed Lorentzian-Gauss function. The measured FWHM values are displayed in Fig. 4.4.16.
This shows that our poly-Si material grown on an AIC seed layer has a signifi cantly improved
crystal quality compared to SPC poly-Si fi lms grown on SiN-coated glass.
5.5
5.0
FWHM [1/cm]
4.5
4.0
3.5
Figure. 4.4.16: Raman measurements on a Si
wafer, on sample SPE-A and on a SPC sample.
The error bars are calculated with 95%
confi dence.
3.0
Si wafer SPE - PECVD SPC -PECVD
UV refl ectance can be used for evaluating the crystal quality. The total hemispherical
refl ectance was measured with our double-beam spectrophotometer (Varian Cary 5G) and
an integrating sphere, in the wavelength range 220–400 nm. The reproducibility of the UV
measurements was very good (± 0.1 absolute %). As can be seen in Fig. 4.4.17, SPE poly-Si
has a signifi cantly better UV refl ectance response than SPC poly-Si. Hence Raman and UV
refl ectance are in agreement with respect to the Si fi lm quality.
75
Si Wafer
70
SPE
Reflection (%)
65
60
55
50
SPC
Figure 4.4.17: UV refl ectance of a polished
singlecrystalline Cz Si wafer (top curve),
sample SPE-A (middle curve), and sample
SPC (lowest curve).
45
210 240 270 300 330 360 390
Wavelength (nm)
Suns-Voc measurements were performed on samples SPE-A, SPE-B and SPC at room
temperature, using illumination of the samples from the glass side (“superstrate confi guration”)
for sample SPE-A and SPC and air-side illumination for sample SPE-B. The measured Suns-Voc
characteristics were fi tted with a 2-diode model (using fi xed diode ideality factors n of 1 and
2) and a shunt resistance (Rsh). For each sample, the shunt resistance was high enough to
not affect the measured Suns-Voc curve. Figure 4.4.18 shows the measured Suns-Voc curve
for sample SPE-A, together with the 2-diode model analysis. We found that the 1-Sun Voc of
SPE-A and SPE-B are both dominated by the n=1 diode, whereas the Voc of sample SPC also
has some infl uence from the n=2 diode. As displayed in Table 4.4.2, the SPC solar cell has a
signifi cantly better 1 Sun-Voc (463 mV) than the SPE solar cells (423 and 393 mV). The 1-
Sun Voc of the SPE diodes are completely dominated by the n=1 diode.
64