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PVD OF n-CuIn3Se5 photoabsorber films

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Key Engineering Materials
Authors:
N. Adhikari
N. Adhikari
S. Bereznev at Tallinn University of Technology
S. Bereznev
J. Kois at Tallinn University of Technology
J. Kois
Olga Volobujeva at Tallinn University of Technology
Olga Volobujeva
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Abstract

Thin films of Cu-In-Se (CISe) photoabsorber with overall composition of CuIn3Se5 were deposited onto glass/ITO substrates by using physical vapour deposition (PVD) technique. Thermal conditions for the substrates during deposition process and following thermal annealing were selected with the purpose to prepare polycrystalline n-CuIn3Se5 photoabsorber layers for the hybrid photovoltaic structures based on inorganic photoabsorber and conductive polymer functional layers. It was found, that the CISe layers deposited at the temperature of substrate of 200 °C and annealed at the temperature range of 450-500 oC in vacuum and double annealed in argon and vacuum at 500 oC demonstrate high photosensitivity and photoconductivity under white light illumination of 100 mW/cm2 intensity. Obtained results show the chalcopyrite structure of prepared photoabsorber films with good adhesion to the glass/ITO substrate.
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PVD OF n-CuIn3Se5 PHOTOABSORBER FILMS
N. Adhikari
1a
, S. Bereznev
1b
, J. Kois
1c
, O. Volobujeva
1d
, T. Raadik
1e
,
R. Traksmaa
2f
, A. Tverjanovich
3g
, A. Öpik
1h
1
Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086 Tallinn,
Estonia
2
Tallinn University of Technology, Materials Research Center, Ehitajate tee 5, 19086 Tallinn,
Estonia
3
Saint-Petersburg State University, 198504 Saint-Petersburg, Staryi Petergof, Ulyanovskaya 5,
Russia
a
nirmaladhikari@hotmail.com,
b
sergei@staff.ttu.ee,
c
julia@staff.ttu.ee,
d
v.olga@staff.ttu.ee,
e
taavi.raadik@ttu.ee,
f
rainer@staff.ttu.ee,
g
andr.tver@yahoo.com,
h
opik@staff.ttu.ee
Keywords: CuIn3Se5; photoabsorber; PVD; annealing
Abstract. Thin films of Cu-In-Se (CISe) photoabsorber with overall composition of CuIn3Se5 were
deposited onto glass/ITO substrates by using physical vapour deposition (PVD) technique. Thermal
conditions for the substrates during deposition process and following thermal annealing were
selected with the purpose to prepare polycrystalline n-CuIn3Se5 photoabsorber layers for the hybrid
photovoltaic structures based on inorganic photoabsorber and conductive polymer functional layers.
It was found, that the CISe layers deposited at the temperature of substrate of 200 °C and annealed
at the temperature range of 450-500 oC in vacuum and double annealed in argon and vacuum at 500
oC demonstrate high photosensitivity and photoconductivity under white light illumination of 100
mW/cm2 intensity. Obtained results show the chalcopyrite structure of prepared photoabsorber
films with good adhesion to the glass/ITO substrate.
Introduction.
During the last two decades, Cu-In-Se (CISe) chalcopyrite photoabsorbers are under serious
investigation as prospective materials for solar cells. These materials have very high optical
absorption coefficient of more than 104 cm-1, easily adjustable bandgap, high stability, and easy n-
and p- type dopability makes its appropriate for PV application [1].
The ordered vacancy compound (OVC) or ordered defect compound (ODC) CuIn3Se5 is a
ternary semiconducting compound belonging to the CISe system [2]. The CuIn3Se5 is a promising
OVC photoabsorber with bandgap of about 1.3 eV which is close to the optimal value for solar cell
applications [3]. The potential application of the CuIn3Se5 photoabsorber in hybrid PV structures
depends on the properties and quality of prepared films e.g. compositional uniformity, crystal
structure, doping density, charge carriers profile etc. Therefore determination of the appropriate
deposition parameters and the deposition technique in detail is very important to prepare optimal
absorber material [4].
The aim of present investigation is connected with developing of n-CuIn3Se5 photoabsorber
layers appropriate for application in hybrid structures based on inorganic photoabsorber and organic
functional layers as an alternative to convenient inorganic solar cell structures. In addition, the
present work is also focused to find appropriate deposition and post-treatment parameters for
CuIn3Se5 photoabsorber layers prepared by PVD.
Key Engineering Materials Online: 2011-11-15
ISSN: 1662-9795, Vol. 495, pp 339-342
doi:10.4028/www.scientific.net/KEM.495.339
© 2012 Trans Tech Publications Ltd, Switzerland
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Structural, optical and photoelectrochemical properties of CuIn3Se5
Article
  • Mar 2008
The morphology, optical characterization and transport properties of dense material CuIn3Se5 have been reported. CuIn3Se5 was synthesized by the fusion technique in a sealed quartz ampoule. The ingots were polycrystalline and the phase crystallizes in a P-chalcopyrite structure. The XRD pattern confirms the formation of the ordered vacancy compound. The composition (Cu = 13.3 at%, In = 31.5 at%, Se = 55.2 at%), established by energy dispersive spectroscopy, is close to the stoichiometric formulation. A band gap of 1.19 eV has been obtained from the diffuse reflectance spectrum. CuIn3Se5 exhibits semi-conducting behavior with an activation energy of 0.52 eV. The thermal variation of the thermopower indicates that the charge carriers are electrons and the conduction occurs predominantly by small polaron hopping. The dissolution rate, determined through dissolved copper, was found to be 1.2 µmol m−2/year in the KCl electrolyte. The results give deeper insights into the photoelectrochemical properties investigated for the first time on the dense material. The capacitance measurement indicates linear behavior from which a flat band potential Vfb of −0.22 VSCE and a doping density ND of 3.75 × 1016 cm−3 were determined. The energy band diagram shows the potentiality for solar energy conversion. The complex impedance pattern is circular in the low frequency region and tends to a straight line in the high frequency one, attributed to the ionic diffusion.
View
Composition dependence of the Raman A1 mode and additional mode in tetragonal Cu–In–Se thin films
Article
  • Sep 2004
Composition dependence of Cu–In–Se films with nominal 60 nm thickness grown on Na-free glass substrates has been systematically investigated by Raman scattering and x-ray diffraction spectra. The most intense A1 mode shift from 175 cm−1 for Cu1.5InSe2 to 151 cm−1 for CuIn5Se8 indicates weakening of the bond-stretching forces with decrease in Cu content. According to the evolution of the phonon frequencies in films, we found that the Raman bands around 160 and 174 cm−1 observed in CuIn5Se8 are probably due to the other ordered structure phase which is very similar to chalcopyrite-related CuIn5Se8. Such coexistence mechanism of both structure phases should be associated with the influence of preferred (112) orientation in the films. Comparing our experimental data with the reported data of the related compounds, we explain the composition effect on phonon frequencies shift from Cu-rich to Cu-poor transition in this paper.
View
Electrodeposited (Cu–In–Se)/polypyrrole PV structures
Article
  • Jul 2006
  • THIN SOLID FILMS
Hybrid PV structures based on polycrystalline photoabsorber Cu–In–Se (CISe) and electrically conductive polymer polypyrrole (PPy) were prepared using the electrodeposition technique. The PPy is considered as p-type barrier layer on n-CISe in the cell structure. Photoactive CISe thin films of various compositions were deposited electrochemically onto glass/ITO substrates from aqueous solutions containing CuSO4, In2(SO4)3 and SeO2. All the obtained polycrystalline CISe films were annealed in vacuum to improve the crystalline structure and etched in 10% KCN to remove the additional phases. In order to prepare the PV structures, thin PPy films doped with β-naphthalene sodium sulfonate were galvanostatically electrodeposited onto the CISe films. Appropriate parameters of electrodeposition were selected experimentally. The morphology and thickness of the prepared film layers were determined using the SEM technique. The chemical composition of the CISe films was determined by energy dispersive X-ray spectroscopy (EDS). To investigate the electrical properties of the obtained structures, current–voltage and impedance characteristics were measured. The best structure showed an open-circuit voltage of 138 mV and a short-circuit current density of 2.55 mA/cm2 under white light illumination with an intensity of 100 mW/cm2.
View
Characterization of stepwise flash evaporated CuIn3Se5 films
Article
  • Feb 2005
  • SOL ENERG MAT SOL C
CuIn3Se5 thin films were grown by stepwise flash evaporation from the polycrystalline powder source. Bulk CuIn3Se5 was synthesized by melt-quench technique, starting from the stoichiometric mixture of constituent elements. Phase purity of the synthesized material was confirmed by powder X-ray diffraction. Structural investigations by transmission electron microscopy (TEM) show that the films grown at 370 K and above were polycrystalline in nature. Compositional analysis by Rutherford backscattering spectrometry (RBS) revealed that the films have near stoichiometric composition. Analysis of optical transmittance data yielded a band gap value of ∼1.26±0.02 eV.
View
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