Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

5/9
Indium sulfide layer characterization
The x-ray diffraction measurements were used to investigate the crystalline structure of the
ultrasonically sprayed indium sulfide layers on SLG substrates. The diffraction patterns of films
prepared with an InCl3 concentration of CIn=0.01 mol/l and In/S ratio variations (1:1, 1:2, 1:3, 1:4) in
the solution at a substrate temperature of Tsurf=200 °C and in 35 min are shown in Figure 2.2. The
films sprayed with sulfur excess, i.e. R[In]:[S]=(1:2,1:3,1:4), showed polycrystalline structure. The inset in
Figure 2.2 shows that the growth rate decreases with the relative increase of sulfur in the precursor
solution. Furthermore it was found, that spraying at various substrate temperatures between 180 °C to
290 °C does not affect the crystalline structure but an increase in the layer growth rate is observed
with rising temperature (not shown here).
Figure 2.2: XRD pattern and growth rate of USP-In2S3 on SLG substrate as a function of the In/S ratio
in the precursor solution deposited at 200 °C. The vertical bars at the x-axis indicate the measured
peaks (circles) and calculated peaks (stars) of randomly orientated tetragonal In2S3 powder.
Figure 2.3: Composition of layers on (111)-Si deposited at different temperatures using solutions of
different In/S precursor ratios as derived from RBS measurements.
To learn more about the effect of the relative sulfur amount in the solution on the layer properties, the
chemical composition of indium sulfide layers sprayed for 20 min at 200 °C with an InCl3 concentration
of CIn=0.01 mol/l and an indium to sulfur ratio of 1:1 and 1:3 was analyzed by RBS and ERDA ion
beam analysis. The atomic concentrations of the elements calculated from RBS spectra are
summarized in Figure 2.3. The films deposited with sulfur deficiency in the precursor solution with
respect to stoichiometric In2S3 show high chlorine concentrations of 20 at% deposited at 200 °C, 16
at% at 220 °C and 13 at% at 240 °C. Two effects can be noted here: (i) the chlorine concentration
decreases with increasing deposition temperature and with increasing sulfur content in the solution; (ii)
with stoichiometric concentration or sulfur excess in the solution the chlorine concentration drops
109/290
ATHLET - Advanced Thin Film Technologies for Cost Effective Photovoltaics, A. N. Tiwari, ETH Zürich