T. YAMAGUCHI ET AL.
Copyright © 2012 SciRes. AMPC
efore, it is presumed that
plications, Cu(In,Ga)Se2 thin films
part by a Grant-in-Aid for Scien-
graded band gap structure . Ther
the value of 1.3 eV demonstrates the bottom of the double
graded band gap structure. This result is suggestive that Cu
(In,Ga)Se2 thin film solar cells with a high Ga/(In+Ga) mole
ratio have a deep valley structure. The deep valley prevents the
carrier collection and causes the deterioration of solar cell per-
formance. The similar tendency for Cu(In,Ga)Se2 thin film
solar cells with Ga/(In+Ga) mole ratio of 0.3 fabricated on Mo
coated Ti foils by three stage process has been reported .
On the other hand, Cu(In,Ga)Se2 thin film prepared at In2S3/
(In2Se3+Ga2Se3)=0.04 demonstrated a band gap of 1.4 eV,
which was suitable for a better matching solar spectrum. Thus
the cell performance was improved. Therefore, In2S3 slightly
supplying is one of the promising methods to improve the per-
formance of Cu(In,Ga)Se2 thin film solar cells.
For photovoltaic device ap
were prepared by sequential evaporation process. The effect of
In2S3 supplying in the third step was examined. XRD study
showed that Cu(In,Ga)Se2 thin films had a chalcopyrite struc-
ture. EPMA analysis demonstrated that Cu(In,Ga)Se2 thin films
have Ga/(In+Ga) mole ratio of 0.855-0.747 and S/(Se+S) mole
ratio of 0-0.04. From SEM micrograph, Cu(In,Ga)Se2 thin films
were formed with small grains. From the quantum efficiency
analysis, Cu(In,Ga)Se2 thin film solar cells with a high Ga/
(In+Ga) mole ratio prepared by sequential evaporation process
had a deep valley structure, which was the most remarkable
point in this study. This result indicates that it is expected to
obtain the improvement in Cu(In,Ga)Se2 thin film solar cells
with a high Ga/(In+Ga) mole ratio by controlling an adequate
double graded band gap structure. The performance of Cu
(In,Ga)Se2 thin film solar cell was improved by using slightly
In2S3 compound in the third step.
This study was supported in
tific Research from the Ministry of Education, Culture, Sports,
Science and Technology in Japan.
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