Secondary phase formation in a Cu2ZnSn(S,Se)4 based p-type layer for photovoltaic applications is one of the major problems which must be overcome to improve solar cell efficiency. To better understand the crystallization mechanism of secondary phases in the material system Cu–Zn–Sn–Se, we investigated the selenization of binary metallic layers as a function of temperature. The sputtered thin film precursors comprise Cu–Zn, Cu–Sn, and Zn–Sn with different sequence. A total six precursors were studied by time-resolved X-ray diffraction while temperature increased from 30 °C to 550 °C. Selenium had been always deposited on top of the metallic precursors in a separate thermal evaporation step. The observed reaction sequences were shown different results depending on the metals which are in first contact with selenium. From these experimental results, the mutual affinities of metals are determined, and a way of reducing the ZnSe crystallization is presented. Preferable precursor composed of ternary metallic layers with Se is also suggested in conclusion with respect to a stacking order of the metals.

The highest efficient Cu 2 ZnSn(S,Se) 4 (CZTSSe) Solar cell have a Cu-poor and Zn-rich metal ratio compared to the stoichiometry. Therefore secondary phases, such as Zn(S,Se), are formed. To investigate a possible correlation between these secondary phases and the solar cell properties, four samples were prepared which have efficiencies of 4.85-6.27%. In the semiconducting CZTSSe films, different amounts of Zn(S,Se) and SnSe 2 are observed, and a correlation with solar cell properties is found. From the experimental results, conclusions about the influence of secondary phases on the cell efficiency are obtained.

Laser scribing of the Mo back electrode is commonly applied to define the cell structure of Cu(In,Ga)(Se,S)2 (CIGSSe) thin film solar cells. The patterning process was performed on laboratory samples using ns and ps pulse length laser processes. After structuring, CIGSSe absorbers were processed by rapid thermal processing (RTP) of stacked elemental layer precursors. Microscopic inhomogeneities were investigated on different sample positions. For samples structured with ns pulse, the absorber morphology in the laser line vicinity is different as compared to the morphology in the unstructured cell area. Scanning electron microscopy and energy-dispersive X-ray spectroscopy show significant changes in the absorber grain size and chemical composition. Close to the laser line, the typically observed Ga accumulation on the back contact is less pronounced and more Ga is incorporated closer to the surface leading to a smaller grain size. The observed changes are attributed to partial damaging of a diffusion barrier between glass and Mo induced by the ns laser process, which allows diffusion of sodium from the glass substrate into the absorber during RTP. The enhanced Ga incorporation closer to the surface is an indication for the influence of sodium on the local phase development during RTP. The damages of the diffusion barrier can be effectively prevented by the application of a ps laser scribing process. CIGSSe absorbers processed on samples structured with ps pulse length do not show the described microscopic inhomogeneities around the laser line.

Cu–Zn–Sn intermetallic thin films were sputtered on Mo-coated soda-lime glass substrates from elemental targets. Samples representing a wide range of compositions around the 2:1:1 kesterite ratio of the Cu–Zn–Sn material system have been investigated. Crystalline phase content and chemical composition of the metal precursors were characterized by X-ray phase analysis and X-ray fluorescence. The metal precursor films were then processed into metal chalcogenides by rapid thermal processing in sulfur ambient with a maximum process temperature around 500°C. Thin films were investigated by X-ray powder diffraction, X-ray fluorescence and Raman spectroscopy to identify their phase contents as a function of precursor composition and initial intermetallic crystalline phase content. Compositional regions of kesterite crystallization as well as remaining secondary chalcogenide phases were identified. Consequences of the obtained results for the thin film crystallization of Kesterite absorbers for solar cell fabrication by rapid thermal processing of metallic precursors will be discussed.

To enhance the conversion efficiency of thin film photovoltaics, chalcopyrite based absorber materials are usually substituted in the cation and anion lattice to yield an absorber with a graded bandgap composed of mixed pentanary crystals Cu(In,Ga)(Se,S)(2). Applying in-situ investigations during the crystallisation of the chalcopyrite is a prerequisite to understand the formation of inhomogeneities and elemental gradients caused by the growth process.The variation of anions yields a combined crystallisation path due to metal sulphoselenides with chalcogen exchange reactions upon heating, i.e. copper sulphoselenides act as a chalcogen buffer and afford substitution of S with Se during annealing. The extended chalcogen substitutions occur due to the complete solid solution of S and Se in Cu(S,Se) and Cu2-x(S,Se). On the contrary, different reaction paths are found for the cations. Although the metals show a good intermixture within the intermetallic alloys featuring In-Ga substitutions, no formation of a mixed or ternary (In,Ga)-chalcogenide is observed. This can be attributed to a narrow solid solution range of the (In,Ga)-chalcogenides. As a consequence the preceding formation of an In-rich and the delayed crystallisation of a Ga-rich chalcopyrite cause a vertical elemental gradient with Ga-accumulation near the back electrode. An interdiffusion of the In-and Ga-rich chalcopyrites is observed for increasing annealing time and temperature. The presented study is focused on quantification of the phase evolution, variation of lattice parameter and diffusion of elements as obtained by Rietveld refinements. (C) 2012 Elsevier B.V. All rights reserved.

The pentanary chalcogenide Cu2ZnSn(S,Se)4 (CZTSSe) compound is attracting considerable attention as a low-cost and high-efficient solar cell. The band gap can be tuned by adding Se to pure kesterite Cu2ZnSnS4, which influences the crystallization kinetics. The investigation of the crystallization of the pure selenium (Se) compound Cu2ZnSnSe4 can be helpful in understanding the reaction path between the elements of CZTSSe. Sputtered Cu-poor intermetallic Cu–Zn–Sn precursors were deposited on Mo-coated polyimide foil and sequentially capped by a thermally evaporated Se layer. Two different amounts of Se were deposited: amount that exactly matches the composition of Cu2ZnSnSe4; and that corresponding to twofold excess of the compound's element ratio. These two compositions were chosen to investigate influences of the amount of Se on the reaction path and kinetics. Also, the reaction of pure metallic Sn with Se was studied by stacking Sn layers on Mo-coated foils for observing a Sn-loss phenomenon. It was also deposited with two different amounts of Se matching approximately the compositions of SnSe and SnSe2. Time-resolved X-ray diffraction was employed to measure the solid state reactions while increasing the sample temperature up to 550°C at a rate of 0.5K/s in an evacuated reaction chamber. After the experiment, sample is analyzed by Raman spectroscopy to distinguish the CZTSe from secondary phases.

In this contribution we report on the development of a two-step process for the formation of Cu2ZnSn(S,Se)4 thin films for solar cells. The two-step formation process of the pentanary kesterite consists of (i) sputter deposition of the metals Cu, Zn and Sn followed by thermal evaporation of chalcogen and (ii) rapid thermal processing of the metal/chalcogen precursors in chalcogen containing ambient. After the absorber formation process, solar cells were processed by deposition of CdS buffer, window layer and metal grid. We evaluated different metal precursor compositions in the ternary Cu–Zn–Sn metal systems regarding their behavior as appropriate precursors for the crystallization of Cu2ZnSn(S,Se)4 absorbers. X-ray diffraction analyses show the presence of secondary chalcogenide phases in absorbers with Cu-poor composition. In combination with Raman spectroscopy, the efficient sulfoselenization could be demonstrated. A broad compositional region is found giving cell efficiencies above 6% via this process route and the potentials for further improvements are discussed. The best solar cell measured so far reached 6.6% efficiency on 1.34cm2 cell size.

Die Erfindung betrifft eine Vorrichtung (10) zum Abscheiden einer aus mindestens zwei Komponenten bestehenden Schicht, insbesondere einer dunnen Schicht, auf einem Gegenstand, insbesondere auf einem Substrat (20). Die Vorrichtung umfasst hierfur eine Abscheidekammer, in der der Gegenstand (20) anordenbar ist, mindestens eine Quelle mit abzuscheidendem Material, die insbesondere in der Abscheidekammer (11) anordenbar oder angeordnet ist und mindestens eine Einrichtung (40) zum Steuern des Abscheidungsprozesses. Ein entsprechendes Verfahren ist ebenfalls vorgesehen. Mit der Vorrichtung und dem Verfahren soll der Abscheidungsprozess gezielt steuerbar sein.

Chalcopyrite based photovoltaic materials Cu(InxGa1-x)(SySe1-y)(2) (CIGSSe) are substituted in the cation and anion lattice to adopt the semiconductor bandgap to the terrestrial solar spectrum. In-situ X-ray diffraction (XRD) investigations on the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se)(2) while annealing stacked elemental layers (SEL) show phase transitions proceeding during the chalcopyrite synthesis. Thin layers of metals with elemental ratio Cu:In:Ga = 3:2:1 are deposited onto Mo-coated polyimide foil by DC-magnetron sputtering. The metal precursor is covered with S and subsequently Se by thermal evaporation of the elements in chalcogen excess (S + Se)/(Cu + In + Ga) = 23. Investigated chalcogen ratios reach from pure Se to pure S. Crystalline phases formed during the annealing of SEL are qualitatively determined. The results are compared to conclusions drawn from previous experiments on Ga-free CuIn(S,Se)(2) absorbers. The presence of Ga and S influences significantly the time-scale and the temperatures of phase transitions, i.e. the sulfoselenisation of precursor phases Cu-16(In,Ga)(9) and Cu-9(Ga,In)(4) proceeds faster with increasing S and is shifted to higher temperatures as compared to Ga-free Cu11In9/Cu16In9. (C) 2011 Elsevier BM. All rights reserved.

Thin-film solar cells based on Cu2ZnSnS4 (CZTS) absorbers were fabricated successfully by solid-state reaction in H2S atmosphere of electrodeposited Cu–Zn–Sn precursors. These ternary alloys were deposited in one step from a cyanide-free alkaline electrolyte containing Cu(II), Zn(II) and Sn(IV) metal salts on Mo-coated glass substrates. The solar cell was completed by a chemical bath-deposited CdS buffer layer and a sputtered i-ZnO/ZnO:Al bilayer. The best solar cell performance was obtained with Cu-poor samples. A total area (0.5 cm2) efficiency of 3.4% is achieved (Voc=563 mV, jsc=14.8 mA/cm2, FF=41%) with a maximum external quantum efficiency (EQE) of 80%. The estimated band-gap energy from the external quantum efficiency (EQE) measurements is about 1.54 eV. Electron backscatter-diffraction maps of cross-section samples revealed CZTS grain sizes of up to 10 µm. Elemental distribution maps of the CZTS absorber show Zn-rich precipitates, probably ZnS, and a Zn-poor region, presumably Cu2SnS3, close to the interface Mo/CZTS.

CIS based chalcopyrite absorber materials are usually substituted in the cation and anion lattice to yield mixed pentanary crystals with the general composition Cu(In,Ga)(Se,S)2 to achieve an optimised adaptation of the semiconductor bandgap to the terrestrial solar spectrum. Real-time investigations during the annealing of stacked elemental layers (SEL) of sputtered metals Cu and In and evaporated chalcogens S and Se with varying ratios were performed by angle-dispersive time-resolved XRD (X-ray diffraction) measurements. After qualitative phase analysis the measured powder diagrams were quantitatively analysed by the Rietveld method, the phases formed determined and their reaction kinetics obtained. Ternary indium and copper sulfoselenides form by the sulfoselenisation of the intermetallic alloy yielding different educts for the chalcopyrite formation with varying sulfur content. For S/(S+Se) ≥ 0.5 the formation of the chalcopyrite CuIn(S,Se)2 is similar to the crystallisation path of CuInS2. With increasing amount of selenium (S/(S+Se) = 0.25) different ternary sulfoselenides contribute to the semiconductor formation. For small amounts of sulfur, i.e. S/(S+Se) ≤ 0.1, the chalcopyrite crystallisation proceeds comparable to the one observed for sulfur-free Cu-In-Se precursors. The formation of CuIn(S,Se)2 is accelerated and proceeds mainly after the peritectic decomposition of Cu(S,Se) to Cu2(S,Se). The sulfur content determines the crystallisation temperature of the semiconductor because Cu(S,Se) decomposes at higher temperatures with increasing sulfur. Upon heating S ↔ Se exchange reactions take place in the Cu-S-Se and Cu-In-S-Se system.

We present results of in-situ X-ray diffraction experiments on the formation of CuInS2 thin film solar cell absorbers. The experiments have been performed while annealing Cu–In–S stacked elemental layer precursors produced by sputtering and thermal evaporation to investigate the crystallisation process of the chalcopyrite CuInS2. Rietveld refinement has been performed to obtain the quantitative phase evolution of crystalline phases while annealing. The annealing process is characterised by a rapid sulfurisation of the initially present intermetallic alloy Cu11In9 forming the sulfide phases CuS, Dg–Cu2−xS, InS and/or CuIn5S8. The chalcopyrite CuInS2 crystallises at elevated sample temperatures by the consumption of these sulfide phases as educts. Three different chalcopyrite formation reactions have been identified by an analysis of the quantitative phase evolution. A comparison to earlier investigations on the formation of CuInSe2 from Cu–In–Se precursors is presented to show similarities and differences of sulfurisation and selenisation processes. The chalcopyrite forms from chalcogenide educts in both cases. However, distinct differences concerning the chalcogenisation kinetics of sulfur and selenium containing Cu–In precursors have been revealed. The chalcogenisation of the intermetallic alloy phase Cu11In9 proceeds extremely fast for Cu–In–S precursors as compared to Cu–In–Se samples.