Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE
Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE
3/5 When In2Se3 layers deposited onto bare soda lime glasses were immersed in the copper solution no ion-exchange reaction occurred and the composition and appearance of the films remained unchanged (to within the accuracy of the EDX measurements). The same was true for In2Se3 layers deposited onto FTO/glass and ITO/glass substrates. When a small piece of Mo/glass was included into the bath, limited incorporation of Cu into the In2Se3 layer was observed (Table 1). Substrate Cu In Se Glass 0.5 45.1 54.4 FTO/Glass 1.2 43.5 55.3 ITO/Glass 0.8 43.7 55.5 Glass (Mo in bath) 5.7 38.0 56.3 Mo/Glass 26.1 28.5 45.4 Table 1: Composition of resulting layers after immersion of In2Se3 layers on various substrate materials into the copper solution. Sufficient copper incorporation was only obtained for substrate materials containing a molybdenum layer. XRD diffractograms are displayed in Figure 1 for samples at three stages of processing. All peaks in the as deposited In2Se3 layer were indexed to the JCPDS files 40-1407 (hexagonal �-In2Se3), 71-0250 (hexagonal In2Se3, calculated) and 42-1120 (Mo). After immersion in the copper solution all but one of the In2Se3 peaks weaken in intensity (relative to the Mo (110) peak). The exception is the peak at 27.6°, identified as the 006 peak (27.592° in 40-0470). Two additional peaks are present in the diffractogram at this stage, one at 26.8° and the other at 44.5°. Both of these peaks are associated with fcc �-Cu2-xSe. The formation of copper selenide with copper in its monovalent state requires that another species in the bath is oxidised. The dependence of the ion-exchange process on the presence of Mo in the bath suggests that the reduction of Cu 2+ ions to Cu + is performed by oxidation of Mo, however this has not been confirmed. After selenization, all peaks were indexed to JCPDS file 40-1487 (CuInSe2). The chalcopyrite peaks (101), (103), (211) and (105/213) are all observed. No significant preferred orientation is calculated from the XRD diffractogram of the selenized sample. There is no evidence of secondary oxide or selenide phases in the diffractogram. Thin Film CIGS Solar Cells with a Novel Low Cost Process, A. N. Tiwari, ETHZ Seite 85 von 288
Seite 86 von 288 Intensity / arb. units Selenized Cu Treated As Deposited 15 20 25 30 35 40 45 50 55 60 65 70 75 2 Theta / degrees Figure 1: X-ray diffraction patterns of an as deposited In2Se3 layer, an In2Se3 layer after copper indiffusion and the same layer after the heat treatment in selenium atmosphere (selenization) showing the formed phases after each process sequence. XPS measurements on the Copper Treated sample showed that it had a graded composition, with peak copper concentration corresponding to minimum In concentration. The Se concentration decreases within the copper containing section of the layer and this is consistent with the formation of Cu2-xSe as it has a higher metal-to-chalcogen ratio than In2Se3. The depth profile of the Selenized sample is broadly homogenised, though a slight increase in the concentration of indium throughout the depth of the sample is observed. EDX measurements on this selenized sample indicated a Cu:In:Se composition of 21.3:30.9:47.8 at%. Concentration / Arb. Units 100 90 80 70 60 50 40 30 20 10 0 C1s O1s Cu2p3 In3d5 Se3d Mo3d 0 2 4 6 8 10 12 14 16 18 20 Etch Time / mins Concentration / Arb. Units 100 90 80 70 60 50 40 30 20 10 0 0 2 4 6 8 10 12 14 16 18 20 Etch Time / mins Cu2p3 In3d5 Se3d Mo3d Figure 2: X-ray photoelectron spectroscopy depth profiles of a copper in-diffused In2Se3 layer before (left) and after (right) the heat treatment in selenium atmosphere. Solar cells processed from selenized precursor films have so far exhibited efficiencies of up to 4%. The IV curve of a solar cell processed from a selenized layer with a Cu:In:Se composition of 20.6:32.6:46.8 at% is shown in Figure 3. Relative to high-performance co-evaporated CuInSe2 solar cells, these cells exhibit low open circuit voltages and fill factors. Thin Film CIGS Solar Cells with a Novel Low Cost Process, A. N. Tiwari, ETHZ 4/5
- Page 38 and 39: 7/9 Fig. 5: Top) SEM micrographs of
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Seite 86 von 288<br />
Intensity / arb. units<br />
Selenized<br />
Cu Treated<br />
As Deposited<br />
15 20 25 30 35 40 45 50 55 60 65 70 75<br />
2 Theta / degrees<br />
Figure 1: X-ray diffraction patterns of an as deposited In2Se3 layer, an In2Se3 layer after copper indiffusion<br />
and the same layer after the heat treatment in selenium atmosphere (selenization)<br />
showing the formed phases after each process sequence.<br />
XPS measurements on the Copper Treated sample showed that it had a graded composition, with<br />
peak copper concentration corresponding to minimum In concentration. The Se concentration decreases<br />
within the copper containing section of the layer and this is consistent with the formation of<br />
Cu2-xSe as it has a higher metal-to-chalcogen ratio than In2Se3. The depth profile of the Selenized<br />
sample is broadly homogenised, though a slight increase in the concentration of indium throughout the<br />
depth of the sample is observed. EDX measurements on this selenized sample indicated a Cu:In:Se<br />
composition of 21.3:30.9:47.8 at%.<br />
Concentration / Arb. Units<br />
100<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
C1s<br />
O1s<br />
Cu2p3<br />
In3d5<br />
Se3d<br />
Mo3d<br />
0 2 4 6 8 10 12 14 16 18 20<br />
Etch Time / mins<br />
Concentration / Arb. Units<br />
100<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
0 2 4 6 8 10 12 14 16 18 20<br />
Etch Time / mins<br />
Cu2p3<br />
In3d5<br />
Se3d<br />
Mo3d<br />
Figure 2: X-ray photoelectron spectroscopy depth profiles of a copper in-diffused In2Se3 layer before<br />
(left) and after (right) the heat treatment in selenium atmosphere.<br />
Solar cells processed from selenized precursor films have so far exhibited efficiencies of up to 4%.<br />
The IV curve of a solar cell processed from a selenized layer with a Cu:In:Se composition of<br />
20.6:32.6:46.8 at% is shown in Figure 3. Relative to high-performance co-evaporated CuInSe2 solar<br />
cells, these cells exhibit low open circuit voltages and fill factors.<br />
Thin Film CIGS Solar Cells with a Novel Low Cost Process, A. N. Tiwari, ETHZ<br />
4/5
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