HAL Id: hal-02138680
https://hal.archives-ouvertes.fr/hal-02138680
Submitted on 24 May 2019
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Heterointerfaces TEM characterization of buffer layers
in KF treated CIGS solar cells. Towards a new buffer
layer?
Eric Gautron, Thomas Lepetit, Sylvie Harel, Ludovic Arzel, Lionel Assmann,
Agathe Frelon, Rodrigo Ribeiro-Andrade, Sascha Sadewasser, Thierry
Douillard, Thierry Epicier, et al.
To cite this version:
Eric Gautron, Thomas Lepetit, Sylvie Harel, Ludovic Arzel, Lionel Assmann, et al.. Heterointerfaces
TEM characterization of buffer layers in KF treated CIGS solar cells. Towards a new buffer layer?.
European Microscopy Congress, Aug 2016, Lyon, France. �hal-02138680�
www.cnrs-imn.fr
Heterointerfaces TEM characterization of buffer layers in KF
treated CIGS solar cells. Towards a new buffer layer?
Eric Gautron
a
, Thomas Lepetit
a
, Sylvie Harel
a
, Ludovic Arzel
a
, Lionel Assmann
a
, Agathe Frelon
a
,
R-Ribeiro Andrade
b
, Sascha Sadewasser
b
, Thierry Douillard
c
, Thierry Epicier
c
and Nicolas Barreau
a
a Institut des Matériaux Jean Rouxel (IMN) UMR6502 CNRS, 2 rue de la Houssinière BP 32229, 44322 Nantes Cedex3, France
b International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga s/n, 4715-330 Braga, Portugal
c Mateis, University of Lyon, INSA de Lyon, UMR5510 CNRS, Bât. Blaise Pascal, F-69621 Villeurbanne Cedex, France
KF treatment involves depletion (Ga, Se, Cu) or segregation (O, K) near the CIGS/CdS
interface, formation of CdSe particles and a diffuse interface. An interface layer composed
mainly of Cd, In, S and O between CIGS and CdS was identified.
A CdIn
2S
4was proved to be a good candidate to replace the « classical » CBD CdS buffer
layer. This allows a complete in-vacuum process which is critical for industry manufacturing.
The next step of this work is to replace Cd by Zn to obtain a ZnIn
2S
4buffer layer in order to
produce solar cells without Cd (for health care consideration).
CIGS solar cell growth with or w/o KF treatment
Photovoltaic performances of CuIn
1-xGa
xSe
2(CIGS) solar cells recently increased with the introduction of a KF treatment between the deposition stages
of the CIGS (p-type semi-conductor) and the CdS (n-type SC) layers. We evidenced on our solar cells that KF treatment involves segregation (O and K)
and depletion (Ga, Se, Cu) near the CIGS/CdS interface and the formation of an interface layer (mainly with Cd, In and S). Based on the composition of
this layer, we proposed to replace the KF treatment and the CdS chemical bath deposition by a single stage of CdIn
2S
4by physical vapor deposition.
CIGSe asorber layer is deposited by a classical « 3-stage » coevaporation process on a sodalime glass SLG/Mo substrate
T em pe ra tur e F lo w In+Ga In+Ga Cu 350 °C 580 °C Time CIGSe CuInGa Se Mo SLG KF evaporation process
CdS CBD
CdS chemical bath deposition (CBD)
CIGSe Mo SLG KF CIGSe Mo SLG CdS CIGSe Mo SLG CdS ???????????????????? Reference sample KF treated sample
CdIn
2
S
4
as a new buffer layer ?
Reference and KF treated cells
Se Ga S Cd Zn O In
50 nm
Se Ga S Cd O In Zn100 nm
0 5 10 15 20 25 30 35 40 0,0 0,2 0,4 0,6 0,8 C o u n ts ( n o rm a liz e d ) Distance (nm) Ga Ka Se Ka Zn Ka O Ka S Ka In La Cd La100 nm
In Ga Se O Zn S Cd20 nm
C IG S Z n OBased on the results obtained on the KF treated sample, an alternative buffer layer made of CdIn2S4was synthesized by physical vapor deposition (PVD). PV characteristics were nearly as good as with a CdS buffer layer obtained by CBD.
Cross section samples were prepared by FIB. Special attention was paid to limit artefacts due to ion beam.
1 2 3 4 5
1 2 3 3+4 5
20 nm
-1 (NH3, thiourea, cadmium acetate dihydrate)ZnO:Al (200 nm) i ZnO (50 nm) CdS (50 nm) CIGSe (2 µm) MoSe2(50 nm) Mo (0.8 µm)
Soda lime glass SLG (1 mm) CIGSe solar cell structure
50 nm
Se Ga S Cd Zn O InFacilities used for this work :
FIB ZEISS NVision40, TEM JEOL 2010 and FEI Titan ETEM (CLYM, Lyon) FIB FEI Helios Nanolab 450S, TEM FEI Themis ChemiSTEM (INL, Braga) PIPS Gatan 691, TEM Hitachi HF 2000 (IMN, Nantes)
EDX mapping of the KF treated sample revealed a depletion of Ga, Se, sometimes Cu and the presence of K at grain boundaries near the CIGS/CdS interface. K and O were detected at this interface. Such behavior was not observed for the reference sample.
K
Few particles were observed in the buffer layer of the KF sample. They are made of CdSe and are covered by a CdS layer.
A thin layer containing Cd, In, S and O separates those CdSe particles from the CIGS layer.
Reference sample KF treated sample
CIGS CdS CIGS CdS
Segregation (O and K) or depletion of elements (Ga, Se and Cu) near interfaces (grain boundaries or CIGS/CdS interface), diffuse interface and formation of CdSe particles in the buffer layer could explain the better PV performances of the KF treated sample. Such performance could also be due to a few nms thick layer composed mainly of Cd, In, S and O between CIGS and CdS (evidenced by EDX, XPS and EXAFS, not shown here).
CIGS/CdS interface is rougher for KF treated sample.
An alternative buffer layer of CdIn2S4was synthesized by PVD. It is made of a 5 nm thick interface layer made of In2S3misaligned planes between CIGS and a well crystallized CdIn2S4layer.
Such stacking is possible because the crystalline structures of CIGS along {112}, In2S3along {111} and CdIn2S4along {111} are very similar.
1 2 3 4 5 CdIn2S4 [11-1] [-12-1] CIGS [1-1-2] [01-1] In2S3 [11-1] ZnO [001] ZA [311] KF treated sample
