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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.

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.

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.

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.

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