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Merdes S.,Helmholtz Center Berlin | Mainz R.,Helmholtz Center Berlin | Klaer J.,Helmholtz Center Berlin | Meeder A.,Sulfurcell Solartechnik GmbH | And 4 more authors.
Solar Energy Materials and Solar Cells | Year: 2011

A Cu(In,Ga)S2-based solar cell with a confirmed efficiency of 12.6% together with an open circuit voltage of 879 mV, prepared from sputtered metals subsequently sulfurized using rapid thermal processing in sulfur vapor, is reported. The performance of the new cell is superior to those obtained previously with multi-source evaporated absorbers. We show that by carefully adjusting the temperature profile, good absorber properties could be transferred from a long process to a rapid thermal process. The improved efficiency is due to an appropriate degree of gallium diffusion toward the surface, which could be achieved despite the short sulfurization time. Absorber and solar cell characteristics are presented. © 2010 Elsevier B.V.All rights reserved.


Fischer C.-H.,Helmholtz Center Berlin | Allsop N.A.,Helmholtz Center Berlin | Allsop N.A.,SULFURCELL Solartechnik GmbH | Gledhill S.E.,Helmholtz Center Berlin | And 10 more authors.
Solar Energy Materials and Solar Cells | Year: 2011

The spray Ion Layer Gas Reaction (ILGAR) process starts with ultrasonic nebulisation of the precursor solution, e.g. InCl3/ethanol for our successful buffer material In2S3. In an aerosol assisted chemical vapour deposition (AACVD) type reaction an In(O,OH,Cl) film is deposited on a heated substrate and is subsequently converted to In 2S3 by H2S gas. The cycle of these steps is repeated until the required layer thickness is obtained. The robust and reproducible process allows a wide control of composition and morphology. Results of this spray-ILGAR method with respect to process, material properties and its application depositing the buffer layer in chalcopyrite solar cells are reviewed. New aspects such as the investigation of the complex chemical mechanism by mass spectrometry, the process acceleration by the addition of H2S gas to the aerosol, the controlled deposition of ZnS nano-dot films and finally the latest achievements in process up-scaling are also included. Solar cells based on industrial Cu(In,Ga)(S,Se)2 absorbers (Avancis GmbH) with a Spray-ILGAR In2S3 buffer reached 14.7% efficiency (certified) and 15.3% with a ZnS/In2S3 bi-layer buffer comparable to reference cells using standard CdS buffer layers deposited by chemical bath deposition (CBD). The quasi-dry, vacuum-free ILGAR method for In2S3 buffer layers is well suited for industrial in-line production and is capable of not only replacing the standard buffer material (the toxic CdS) but also the often slow CBD process. A tape coater for 10 cm wide steel tape was constructed. It was shown that In 2S3 layers could be produced with an indium yield better than 30% and a linear production speed of 1m/min. A roll-to-roll pilot production line for electrochemically deposited Cu(In,Ga)Se2 with ILGAR buffer is running in industry (CIS-Solartechnik, Hamburg). A 30x30 cm 2 prototype of an ILGAR in-line coater developed by Singulus and Helmholtz Zentrum Berlin is currently being optimised. First 30×30 cm 2 encapsulated modules achieved efficiencies up to 13.0% (CdS buffered reference 13.3%). © 2010 Elsevier B.V. All rights reserved.


Fu Y.,Helmholtz Center Berlin | Allsop N.A.,Helmholtz Center Berlin | Allsop N.A.,SULFURCELL Solartechnik GmbH | Gledhill S.E.,Helmholtz Center Berlin | And 6 more authors.
Advanced Energy Materials | Year: 2011

Wurtzite-phase ZnS nanodot films with controllable dot density can be prepared at low temperature by a technique known as Spray-ILGAR (ILGAR = ion-layer gas reaction), without organic surfactant. ZnS nanodots covered with homogenous In 2S 3 (as the point-contact bridge) act as a defect passivation layer and form a structured buffer layer. This ZnS/In 2S 3 buffer improves cell efficiencies by up to about 1%-1.5% compared to reference cells with a pure ILGAR In 2S 3 buffer. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wilchelmi K.,Sulfurcell Solartechnik GmbH | Forster D.,Sulfurcell Solartechnik GmbH | Neisser A.,Sulfurcell Solartechnik GmbH | Schomacker R.,TU Berlin
Journal of the Electrochemical Society | Year: 2010

The chemical bath deposition of metal sulfide, especially CdS, is the most common way of growing buffer layers in the chalcopyrite photovoltaic solar cells. From the kinetic point of view, the reactions should always be reproducible with the same initial reactant concentration of thiourea, ammonia, and cadmium salt, the same temperature, and the same deposition time. But different reaction kinetics of CdS molecule formation and deposition is observed. Different thiourea lots with nominally the same purity show different kinetics of the reaction and resulting CdS layer thicknesses after the reaction. © 2010 The Electrochemical Society.


Grimm A.,Helmholtz Center Berlin | Just J.,Helmholtz Center Berlin | Kieven D.,Helmholtz Center Berlin | Lauermann I.,Helmholtz Center Berlin | And 4 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2010

In an effort to eliminate the standard CdS buffer layer from chalcopyrite-based thin film solar cells we have investigated sputtered Zn(O,S) films. They were prepared by partially reactive sputtering from a ZnS target in an argon/oxygen mixture. Single phase, polycrystalline films were achieved for substrate temperatures of at least 100 °C. Test devices prepared in a completely dry process showed superior blue response and active area conversion efficiencies up to 13.7%. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Merdes S.,Helmholtz Center Berlin | Johnson B.,Helmholtz Center Berlin | Saez-Araoz R.,Helmholtz Center Berlin | Ennaoui A.,Helmholtz Center Berlin | And 5 more authors.
Materials Research Society Symposium Proceedings | Year: 2010

In a previous work, Cu(In,Ga)S2 thin films prepared by rapid thermal sulfurization of metallic precursors yielded solar cells with efficiencies reaching 12.9%, a short circuit current density of 22.3 mA/cm 2 and open circuit voltages up to 850 mV. However, the fill factor was close to, but typically did not exceed 70%. In this contribution we report on the role of junction formation by chemical bath deposition on these parameters. Concentrations in the bath and deposition times were varied. A comparison is made between CdS and Zn(S,O) buffer layers. The influence of the incorporated gallium on surface properties was investigated by ultraviolet photoelectron spectroscopy (UPS) for the valence band edge and near edge X-ray absorption fine structure (NEXAFS) for the conduction band edge. Even in our best cell (13.1%) the activation energy of the saturation current is found to be still smaller than the band gap. High diode ideality factors and voltage dependent current collection prevent higher fill factors. © 2009 Materials Research Society.


Hotz T.,University of Gottingen | Marnitz P.,University of Gottingen | Stichtenoth R.,University of Duisburg - Essen | Stichtenoth R.,Sulfurcell Solartechnik GmbH | And 4 more authors.
Computational Statistics and Data Analysis | Year: 2012

It is shown how to choose the smoothing parameter in image denoising by a statistical multiresolution criterion, both globally and locally. Using inhomogeneous diffusion and total variation regularization as examples for localized regularization schemes, an efficient method for locally adaptive image denoising is presented. As expected, the smoothing parameter serves as an edge detector in this framework. Numerical examples together with applications in confocal microscopy illustrate the usefulness of the approach. © 2011 Elsevier B.V. All rights reserved.


Grimm A.,Helmholtz Center Berlin | Kieven D.,Helmholtz Center Berlin | Klenk R.,Helmholtz Center Berlin | Lauermann I.,Helmholtz Center Berlin | And 3 more authors.
Thin Solid Films | Year: 2011

In an effort to eliminate the CdS buffer layer and its costly preparation process we are considering sputtered buffer layers. In particular, we report in this contribution on the reactive sputtering of wide gap Zn(O,S) compound semiconductors and their application in solar cells with different types of chalcopyrite absorbers. While we were able to freely adjust the composition through the oxygen partial pressure, the structural and optical properties are superior when the composition is close to the ternary endpoints. Open circuit voltage and short circuit current density as a function of Sulphur content in the buffer show opposite trends. Working cells were achieved with low band gap as well as wide band gap absorbers, however, their performance is so far inferior to that of the standard stacks. © 2011 Elsevier B.V. All rights reserved.


Meeder A.,Sulfurcell Solartechnik GmbH | Schmidt-Weber P.,Sulfurcell Solartechnik GmbH | Hornauer U.,Sulfurcell Solartechnik GmbH | Forster D.,Sulfurcell Solartechnik GmbH | And 5 more authors.
Thin Solid Films | Year: 2011

Sulfurcell (SC) has been running a pilot production for thin-film solar modules using CuInS2-chalcopyrite (CIS) as absorber material since 2004. Since then production technology has been constantly improved with module power values exceeding 64 W, corresponding to an aperture area efficiency level of about 9%. Small area (0.5 cm2) cells cut out of such CIS modules reach maximum efficiencies close to 11%. Strong efforts have been made to develop a new sequential Cu(In,Ga)S2 (CIGS) process suitable for production of large-scale CIGS solar modules thereby enabling module efficiencies above 10%. CIGS-based solar cells are-quite similar to CIS-based modules-prepared from sputtered metals subsequently sulfurized using rapid thermal processing in sulfur vapor. Such Cu(In,Ga)S2 solar cells reach material record efficiencies about 13%. The cells are characterized by high open-circuit voltages up to 890 mV. Based on the results of the "Helmholtz Zentrum Berlin" (HZB), Sulfurcell has successfully scaled this process to our typical module size of 125 cm × 65 cm and is currently piloting the process for mass production. This paper will give an overview of electrical and structural parameters of world's first large-scale CIGS modules. CIGS module and cell parameters will be compared with standard CIS module and cell parameters and measured CIGS efficiency temperature coefficients will be compared with typical temperature coefficients of modules based on established PV technologies. © 2011 Elsevier B.V.


Merdes S.,Helmholtz Center Berlin | Mainz R.,Helmholtz Center Berlin | Rodriguez-Alvarez H.,Helmholtz Center Berlin | Klaer J.,Helmholtz Center Berlin | And 4 more authors.
Thin Solid Films | Year: 2011

Rapid thermal sulfurization of metallic precursors has proven to be a successful method for the preparation of Cu(In,Ga)S2 based solar cells. However, during the sulfurization, several problems can be encountered. Due to the difference in reaction rates between ternary sulfides, the process can result in absorbers with a layered CuInS2/CuGaS2 structure or slow and incomplete sulfurization that leads to samples where an unreacted Cu-Ga metallic phase remains at the back of the sample. The formation kinetics of single phase Cu(In,Ga)S2 is a complex process which depends on several parameters. In this work, we focus on the influence of precursor stacking and investigate the growth of Cu(In,Ga)S2 thin films using scanning electron microscopy and X-ray diffraction. It is observed that precursor alloying occurs prior to sulfurization and that the Cu(In,Ga)S2 compound is formed by the interdiffusion of the ternary CuInS2 and CuGaS2 phases. Correlation between the structural properties of the precursors/absorbers and the obtained solar cells is made. © 2011 Elsevier B.V.

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