Spectroscopic investigation of the deeply buried Cu In,Ga S,Se 2 Mo interface in thin film solar cells

The Cu In,Ga S,Se 2 Mo interface in thin film solar cells has been investigated by surface sensitive photoelectron spectroscopy, bulk sensitive X ray emission spectroscopy, and atomic force microscopy. It is possible to access this deeply buried interface by using a suitable lift off technique, which allows to investigate the back side of the absorber layer as well as the front side of the Mo back contact. We find a layer of Mo S,Se 2 on the surface of the Mo back contact and a copper poor stoichiometry at the back side of the Cu In,Ga S,Se 2 absorber. Furthermore, we observe that the Na content at the Cu In,Ga S,Se 2 Mo interface as well as at the inner grain boundaries in the back contact region is significantly lower than at the absorber front surfac

Comprehensive Comparison of Various Techniques for the Analysis of Elemental Distributions in Thin Films

The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limit

Synchrotron based spectroscopy for the characterization of surfaces and interfaces in chalcopyrite solar cells

In this paper we describe synchrotron based state of the art spectroscopic methods for the analysis of surfaces and interfaces in thin film photovoltaic devices, their merits and their limitations. Using results obtained with the CISSY end station at the BESSY synchrotron in Berlin, Germany, we show how surface sensitive Synchrotron excited X ray Photoelectron Spectroscopy SXPS and Soft X ray Emission Spectroscopy SXES , which yields compositional and chemical depth information in the tens to hundred nm scale, have increased our knowledge of the chemistry of surfaces and buried interfaces of these system

Formation of Cu2ZnSnS4 and Cu2ZnSnS4 CuInS2 thin films investigated by in situ energy dispersive X ray diffraction

Chalcopyrite CuInS2 and the structurally related kesterite Cu2ZnSnS4 are known as photovoltaic absorber materials. In this study different precursor thin films of the quaternary Cu Zn Sn S system stacking Mo CuS ZnS SnS and of the pentenary Cu In Zn Sn S system stacking Mo CuIn ZnS SnS were annealed in sulfur atmosphere. The predominant crystalline phases were detected by in situ energy dispersive X ray diffraction EDXRD . Additionally the X ray fluorescence signals of the film components were recorded to detect diffusion effects. For the quaternary system we found ZnS, CuS, Cu2 xS, Sn2S3 and SnS as main binary phases during annealing. The Sn2S3 SnS phase transition had a significant impact on the later formation of ternary quaternary phases. A high diffusivity of copper can explain the little influence of the precursor stacking on the reaction path and may also be responsible for the poor adhesion of the films. For annealing temperatures above 450 C Cu2ZnSnS4 can be identified clearly by XRD. The incorporation of indium in the system leads to new diffraction peaks which can be explained by the formation of solid solutions in the system CuInS2 Cu2ZnSnS

Multi stage evaporation of Cu2ZnSnS4 thin films

Multi stage evaporation is a well established method for the controlled growth of chalcopyrite thin films. To apply this technique to the deposition of Cu2ZnSnS4 thin films we investigated two different stage sequences A using Cu2SnS3 as precursor to react with Zn S and B using ZnS as precursor to react with Cu Sn S. Both Cu2SnS3 and ZnS are structurally related to Cu2ZnSnS4. In case A the formation of copper tin sulphide in the first stage was realized by depositing Mo SnSx CuS 1 lt;x lt;2 and subsequent annealing. In the second stage ZnS was evaporated in excess at different substrate temperatures. We assign a significant drop of ZnS incorporation at elevated temperatures to a decrease of ZnS surface adhesion, which indicates a self limited process with solely reactive adsorption of ZnS at high temperatures. In case B firstly ZnS was deposited at a substrate temperature of 150 C. In the second stage Cu, Sn and S were evaporated simultaneously at varying substrate temperatures. At temperatures above 400 C we find a strong decrease of Sn incorporation and also a Zn loss in the layers. The re evaporation of elemental Zn has to be assumed. XRD measurements after KCN etch on the layers prepared at 380 C show for both sample types clearly kesterite, though an additional share of ZnS and Cu2SnS3 can not be excluded. SEM micrographs reveal that films of sample type B are denser and have larger crystallites than for sample type A, where the porous morphology of the tin sulphide precursor is still observable. Solar cells of these absorbers reached conversion efficiencies of 1.1 per cent and open circuit voltages of up to 500 m