Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE

5/5
Current density / mA.cm -2
100
80
60
40
20
0
-20
�=4.1%
FF=51.1%
J =28.5 mA/cm sc 2
V =284 mV
oc
Area=0.6cm 2
-40
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Voltage / V
Figure 3: Current-Voltage curve of the solar cell with the highest efficiency so far of the performed
experiments.
One of the weaknesses cited for the Clevite process was that defects in the CdS layer caused preferential
diffusion and led to localised inhomogeneities in the Cu2S layer. However, the high diffusion
coefficient of Cu in In2Se3 at elevated temperatures [5] should reduce this effect significantly.
Evaluation of 2007 and perspectives for 2008
The low-temperature incorporation of Cu into In2Se3 layers by ion-exchange from aqueous solution
was reported. This process results in thin films with a graded composition containing the crystalline
phases �-Cu2-xSe and �-In2Se3. Annealing the films in the presence of Se vapour formed chalcopyrite
CuInSe2 and homogenised the depth profile of the films. The results demonstrate a potential lowtemperature
route to the formation of a precursor structure for CuInSe2 thin films. However, the ionexchange
solution was destructive to the Mo back contact and attempts to use alternative contacts
resulted in no incorporation of Cu into the In2Se3 films. The obtained layers are free of oxygen and
carbon impurities and do not show any evidence of detrimental binary chalcogenide phases after the
annealing step in selenium vapour.
Further work is required to determine the reaction kinetics of the process and develop an improved
solution in which the contact to the In2Se3 is stable. The reaction kinetics of the precursor film to the
CIGS compound contains several phase transitions which may have positive and negative influences
on the final CIGS properties.
References
[1] AM. Gabor, JR. Tuttle, DS. Albin et al. High Efficiency CuInxGa1-xSe2 Solar-Cells made from (Inx,Ga1-x)2Se3 precursor
films, Applied Physics Letters 65 (2), 198-200, 1994
[2] MA. Contreras, K. Ramanathan, et al. Diode characteristics in state-of-the-art ZnO/CdS/Cu(In(1-x)Gax)Se2 solar cells
Progress in Photovoltaics 13, 209-216, 2005
[3] J. Kessler, D. Schmid, S. Zweigart, H. Dittrich, HW. Schock, CuInSe2 film formation from sequential deposition of
In(Se):Cu:Se, 12th European Photovoltaic Solar Energy Conference (1994) 648-652.
[4] A. Ali, NA. Shah, AKS. Aqili, A. Maqsood, Investigation of Cu-containing low resistivity CdTe thin films deposited by
the two-source evaporation technique, Semiconductor Science and Technology 21 (2006) 1296-1301,
[5] K. Djessas, S. Yapi, G. Masse, et al. Diffusion of Cu, In, and Ga in In2Se3/CuGaSe2/SnO2 thin film photovoltaic structures,
Journal of Applied Physics 95 (8): 4111-4116, 2004
Thin Film CIGS Solar Cells with a Novel Low Cost Process, A. N. Tiwari, ETHZ Seite 87 von 288