Amorphous Silicon Solar Cell Techniques for High Temperature and/or Reactive Deposition Conditions
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Mat. Res. Soc. Symp. Proc. Vol. 557 © 1999 Materials Research Society
amorphous silicon protection layers for solar cells deposited in the n-i-p deposition sequence. Where, in this n-i-p case the goal was to protect an amorphous p-layer from oxidation during the sputter deposition of the ZnO top contact. EXPERIMENT P-i-n and n-i-p solar cells were prepared on various substrates using a previously described [6] deposition system which had the ability to deposit amorphous and microcrystalline silicon layers using either RF, VHF or MW remote plasma enhanced chemical vapor deposition. In order to examine and improve the resistance of TCO coated glass substrates p layers, and complete p-i-n and n-i-p solar cells were prepared. The p-i-n solar cells were prepared on TCO coated glass substrates and employed p-[LX-Si:B layers. Prior to incorporation into the solar cell the p-ptX-Si:B was optimized by analysis of films deposited onto glass substrates using VHF-
(144MHz) plasma assisted CVD as a function of temperature. The i- and n-layers of all solar cells studied in this work were prepared by conventional RF-CVD at 200'C. Raman analysis indicated that films deposited with SiH4 to H2 ratios of 1% had significant crystalline silicon contents(as well as an a-Si:H matrix). Each substrate was arranged to have a surface area comprised of un-coated Asahi U type SnOx, Ga-doped ZnO and Cr over coated SnOw; as well as, both Cr and Ga-doped ZnO over coated AsahiTM U-type SnOx regions as shown in Fig.la. In the case of n-i-p solar cells prior to the sputter deposition of Ga-doped ZnO, Cr was c-beam deposited onto a region of the intended solar cell surface as shown in Fig. lb.
n
top electrode
Ir
top electrode
Cr
p
Cr
F[
Ga-ZnO
Asahi U-Type
n Asahi U-Type
(a)
(b)
Figure 1 Configuration of SnOx coated substrates and the various protective layers used in this study for the p-i-n case (a), and the application of Cr protective layers to selected surface areas of p-layers of n-i-p deposition sequence solar cells (b).
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RESULTS AND DISCUSSIONS To identify the hydrogen dilution and other conditions necessary for the deposition of pliX-Si:B layers were systematically deposited onto glass substrates as a function of dilution ratio and substrate temperature. The Raman spectra of this series of films is shown in Fig. 2. It is noted that all samples contained some amorphous fraction. However, large a-Si:H content is expected in such thin films. For the evaluation of substrate hydrogen plasma resistance and solar cell optimization the 1% Sill in H2 dilution at 220 and 300 TC were identified for further study. SIH 4IH2=1%
350
SIH4 /H2 =2%
.•250 300C
300-
2t0
200
300C
280C
220QC
21
2000080
COC
2100 1500 100500
200
400 600 Raman Shift [cm-']
800
200
400 600 Raman Shift [cm-1]
800
Figure 2 The Raman spectra of p-[tX-Si:B layers deposited at 1 and 2% SiI- 4 in H2 as a function of substrate temperature (as indicated). Figure 3 shows the solar cell parameters of p-i-n solar cells having an Asahi7 " U-type substra
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