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Whilst Cu(In,Ga)Se2 (CIGSe) is an extremely promising material for solar cell fabrication, the widening of the band gap beyond the standard 1.1 eV is highly desirable for semitransparent applications. By replacing Cu with Ag and increasing the Ga content, we fabricate ACIGSe absorbers with band gaps ranging from 1.27–1.55 eV. An Ag/(Ag + Cu) ratio from 0.36–1.00 is chosen, as well as a Ga/(Ga + In) ratio from 0.25–0.59. The larger Ag and Ga contents lead to the expected band gap widening, which is, together with high sub-gap transparency, essential for semitransparent applications. The crystalline properties are confirmed by Raman spectroscopy and X-ray diffraction, which both reveal peak shifts according to the composition variations: a higher Ag content results in lower Raman shifts as well as in lower angles of X-ray diffraction for the main peaks due to the larger mass of Ag compared to Cu and the larger lattice constant of Ag-rich compounds. Increased open circuit voltages and decreased short circuit current densities are confirmed for higher band gaps. An overall trend of increased power conversion efficiency of the related devices is promising for future research of wide band gap Ag-chalcopyrites and their semitransparent application. [ABSTRACT FROM AUTHOR]

Vacuum free, solution based routes to the preparation of chalcopyrite absorbers for solar cells promise options in device design and manufacturing that are not provided by the standard vacuum based approaches. In order to fully exploit these options, the precursor should contain neither nanoparticles nor hazardous chemicals, and it should be stable under ambient conditions. In this contribution we report on CuIn(S,Se)2 thin film preparation based on spin coating of an air stable molecular ink containing metal chlorides and thiourea in organic solvents. Several key parameters directly influencing the performance of the resulting solar cells have been identified. Wetting of the glass/Mo substrate has been adjusted by varying the concentration of ethylene glycol butyl ether in the ink. Before annealing in Ar/Se at atmospheric pressure, several cycles of ink deposition and drying can be used to increase the thickness of the precursor stack. Careful balancing of ink concentration, number of precursor deposition cycles, and annealing temperature profile will transform the multi-layer precursor into a sufficiently thick, continuous, large grained film as required for high quantum efficiency, and good red response of the cells. These optimizations aimed at high photo current have already led to an efficiency of 9.5%. [ABSTRACT FROM AUTHOR]

Abstract: The sequential and cyclic spray ion layer gas reaction (spray-ILGAR) technique allows the deposition of metal chalcogenide films controllable from monodispersed nanodots to homogeneous compact layer. With access to this technique, a structured buffer layer for Cu(In,Ga)(S,Se)2 cells, named “defect passivation/point contact bilayer buffer” is introduced at the heterogeneous interfaces to replace the conventional toxic CdS buffeProd. Type: FTPr material and to improve the pure In2S3 buffer. Here, the spray-ILGAR ZnS nanodots serve as a passivation layer with a reduced interface recombination, while the compact spray-ILGAR In2S3 film on top and in-between the nanodots acts as point contact layer for the charge carrier transport. The optimal ZnS dot density and In2S3 thickness are determined and discussed in detail. As yet, the solar cell efficiency with ZnS/In2S3 buffer layer can be improved by about 1.5% absolutely as compared to a pure In2S3 buffered cell. Apart from the electronic properties of the absorber/buffer interface, also the chemical and diffusion processes during junction formation, which may influence the properties of the completed solar cell, are investigated and discussed. [Copyright &y& Elsevier]

Abstract: 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 In2S3 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 10cm wide steel tape was constructed. It was shown that In2S3 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 30x30cm2 prototype of an ILGAR in-line coater developed by Singulus and Helmholtz Zentrum Berlin is currently being optimised. First 30×30cm2 encapsulated modules achieved efficiencies up to 13.0% (CdS buffered reference 13.3%). [Copyright &y& Elsevier]