The successful implementation of two new process steps into an existing Cu(In,Ga)(Se,S)(2) (CIS) production line was achieved. One, a newly developed back contact, aims for a better process control, as far as the transition of the metallic back contact to a selenide/metal bi-layer during CIS-formation is concerned. This was done by the introduction of a corrosion resistant barrier layer, which reliably stops chalcogenide diffusion from the top. By doing so, a back contact layer is obtained, with well defined properties in which the functionalities of the back electrode now is divided between two separated layers. The other development presented in this paper, tackles the complexity of CIS-module production and the interferences between the different processes required. By shifting the P1-scribing process after i-ZnO deposition, the process sequence for CIS is simplified and it will be shown that this new P1i exhibits superior properties as far as CIS morphology and groove quality is concerned. (C) 2015 The Japan Society of Applied Physics

A new mass production technology for CIS-absorber formation yielding high-average module efficiencies is introduced. A novel custom-designed oven very successfully exploits the principle of forced convection during heating, CIS formation reaction, and cooling. Cu(In,Ga)(Se,S) 2 absorbers are formed by metal precursor deposition on soda lime glass followed by reaction in selenium/sulfur atmosphere. Processing is performed in a multiple-chamber equipment which handles corrosive, flammable, and toxic process gases from atmospheric pressure to vacuum at high durability. The substrates (size: 50 cm × 120 cm) are processed in batches up to 102 substrates, applying forced convection for very homogenous heat transfer and high heating and cooling rates. Multiple-chamber design and batch size yield high throughput at cycle times above 1 h. This approach combines the specific advantages of batch type and inline processing. An excellent average efficiency of 14.3% with a narrow distribution (+/-0.31%) and a peak efficiency of 15.1% is shown with this technology. Module characteristic distributions during pilot production are presented. Detailed layer analytics is discussed. This straightforward reliable mass production technology is a key for highest module performance and for upscaling. Module efficiencies of 17% can be reached, enabling production costs below 0.38 US$/Wp in a projected GWp plant.

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 limits.

Centrotherm photovoltaics AG has chosen Cu(In,Ga)Se2 (CIGS) as material system for turnkey thin-film photovoltaic production lines because of its great potential concerning conversion efficiencies and economical production. Within CIGS thin-film technology, centrotherm overcomes several disadvantages of former technologies with a unique technology for the CIGS absorber layer formation. The new technology is based on sputter technology on one hand side and a rapid thermal process on the other side. Precursor metal layers are sputtered on large area and transformed to semiconducting CIGS in an ultra rapid thermal process step, which is performed under atmospheric pressure conditions. This leads to unreached short process time on the order of 1 minute and hence to a very high productivity, and prerequisites for real mass production on the GW scale.

The best CZTS solar cell so far was produced by co-sputtering continued with vapour phase sulfurization method. Efficiencies of up to 5.74% were reached by Katagiri et al. The one step electrochemical deposition of copper, zinc, tin and subsequent sulfurization is an alternative fabrication technique for the production of Cu2ZnSnS4 based thin film solar cells. A kesterite based solar cell (size 0.5 cm(2)) with a conversion efficiency of 3.4% (AM1.5) was produced by vapour phase sulfurization of co-electroplated Cu-Zn-Sn films. We report on results of in-situ X-ray diffraction (XRD) experiments during crystallisation of kesterite thin films from electrochemically co-deposited metal films. The kesterite crystallisation is completed by the solid state reaction of Cu2SnS3 and ZnS. The measurements show two different reaction paths depending on the metal ratios in the as deposited films. In copper-rich metal films Cu3Sn and CuZn were found after electrodeposition. In copper-poor or near stoichiometric precursors additional Cu6Sn5 and Sn phases were detected. The formation mechanism of Cu2SnS3 involves the binary sulphicles Cu2 -xS and SnS2 in the absence of the binary precursor phase Cu6Sn5. The presence of Cu6Sn5 leads to a preferred formation of Cu2SnS3 Via the reaction educts Cu2-xS and SnS2 in the presence of a SnS2(Cu4SnS6) melt. The melt phase may be advantageous in crystallising the kesterite, leading to enhanced grain growth in the presence of a liquid phase. (C) 2008 Elsevier B.V. All rights reserved.

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<x<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 degrees C. In the second stage Cu, Sn and S were evaporated simultaneously at varying substrate temperatures. At temperatures above 400 degrees 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 degrees 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% and open circuit voltages of up to 500 mV. (C) 2008 Elsevier B.V. All rights reserved.

Phase transformations of GaxSy−(Cu,In) thin film stacks annealed in sulphur vapour were investigated by in-situ energy dispersive X-ray diffraction (EDXRD) in order to monitor the Ga incorporation into the resulting quaternary Cu(In,Ga)S2 alloy. The partial replacement of In by Ga in the chalcopyrite structure widens the band gap of the material. Thereby the open circuit voltage of corresponding devices can be enhanced. In the present study Ga was supplied by an amorphous or crystallized (GaxSy)-layer, deposited by thermal evaporation of Ga2S3 before sputtering elemental Cu and In precursor layers. The sulphurisation was carried out in a specially designed vacuum chamber which can be attached to the synchrotron beamline F3 at Hasylab (Hamburg). The evolution of the different phases during sulphurisation of the GaxSy−(Cu,In) precursors, as observed via EDXRD, indicated the almost simultaneous occurrence of two stacked chalcopyrite phases which are Ga-rich and In-rich. For longer annealing times the EDXRD-spectra show the appearance of a third, intermediate Cu(In,Ga)S2 phase. Monitoring the peak position during the annealing stage allows evaluating the lattice parameters as a function of annealing time. Thereby the In–Ga interdiffusion between the different chalcopyrite phases can be investigated.

Cu(In,Ga)(S,Se) 2 (‘CIGSSe’) based solar cells with a ZnO window extension layer (WEL) deposited by the ion layer gas reaction (ILGAR) reach competitive efficiencies compared to corresponding references with CdS buffer and lead to a simplified device structure. The WEL replaces not only the CdS buffer, but also the undoped part of the usually applied rf ‐sputtered ZnO window bi‐layer. The long‐term stability of CIGSSe‐based solar modules is currently under investigation. In order to pass the respective stability tests, which include exposure to ‘damp‐heat’ (DH) conditions (85% relative humidity at 85(C) to accelerate possible aging effects, a good intrinsic material stability is required. In Reference 1 it was revealed, that ILGAR‐ZnO contains a certain amount of meta‐stable hydroxide, which can be directly tuned by the ILGAR process parameters (number of process cycles and process temperature). In order to determine the ILGAR process parameters, which result in intrinsically stable WELs, ILGAR‐ZnO/CIGSSe test structures were investigated by means of scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) before and after a DH‐test. It was found that, induced by the DH‐conditions, a continuous dehydration of the WELs together with a disintegration of the ILGAR‐ZnO layers takes place. This supports an earlier suggested mechanism of a DH‐induced degradation by a release of water at the most critical location in a solar cell, at the heterointerface between window and absorber. By a systematic variation of the ILGAR process parameters it was possible to reduce the hydroxide content in the ILGAR‐ZnO layers resulting in intrinsically more stable samples. Copyright © 2006 John Wiley & Sons, Ltd.

The system CuGaSe2–CuGa3Se5 in thin films has been investigated. Layer synthesis was carried out by chemical close-spaced vapour transport (CCSVT) using Cu precursors on Mo/soda-lime glass substrates. The extension of deposition times in a two-step process led to final film compositions with [Ga]/[Cu] ratios ranging from 1 to 3, allowing the study of the phase transition mentioned above. Films showing chalcopyrite (1:1:2), OVC (1:3:5) and both phases were grown. X-ray emission spectroscopy and X-ray diffraction (XRD) techniques have been combined for a compositional and structural study of this material system probing both bulk and near surface properties of the films. This analysis was also extended to the rear-surface investigation of selected two-phase thin films and complemented with surface sensitive photoelectron spectroscopy (PES). From these results a growth model is presented for CuGa3Se5 formation in gallium rich, CCSVT-grown CuGaxSey-films.

Cu ( In , Ga ) ( S , Se ) 2 (CIGSSe) based solar cells with a ZnO window extension layer (WEL) deposited by the ion layer gas reaction (ILGAR) reach competitive efficiencies compared to corresponding references with CdS buffer and lead to a simplified device structure. The WEL replaces not only the CdS buffer, but also the undoped part of the usually applied rf-sputtered ZnO window bilayer. Since the performance of corresponding solar cell devices depends strongly on the ILGAR process parameters (number of deposition cycles and process temperature), respective ILGAR-ZnO∕CIGSSe test structures were investigated by means of scanning electron microscopy and x-ray photoelectron spectroscopy. Thereby, the growth mechanism of ILGAR-ZnO on CIGSSe absorbers and its morphology was investigated. In addition, the surface composition was determined, showing that ILGAR-ZnO layers contain a certain amount of metastable hydroxide. Due to the systematic variation of the ILGAR process parameters it could be demonstrated that it is possible to directly tune the hydroxide content in the ILGAR-ZnO layers.

This article investigates the role of the interfaces of CdS and In(OHx,Sy) buffer layers in thin film ZnO/buffer/Cu(In,Ga)Se2 heterojunction solar cells. The presence of acceptor defects at the ZnO/In(OHx,Sy) interface explains the poor performance of solar cells using the In(OHx,Sy) buffers. The standard CdS buffer has better quality at both interfaces to the ZnO window layer and to the Cu(In,Ga)Se2 absorber. By using a combination of buffer layers of thin CdS and In(OHx,Sy), the short circuit current density is improved by 2 mAcm−2 and thus, the efficiency is 1% higher than that of devices with the standard CdS buffer.