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A multidisciplinary approach towards advanced transparent conductive electrodes

: Szyszka, B.; Georg, A.; Löbmann, P.; May, C.; Elsaesser, C.

Glass Performance Days 2009 : Professionals, Products, Processing; Conference Proceedings; Tampere, Finland, 12 - 15 June 2009
Tampere, 2009
ISBN: 978-952-5836-01-1
International Conference on Architectural and Automotive Glass <11, 2009, Tampere>
Conference Paper
Fraunhofer IST ()
Fraunhofer IPMS ()
Fraunhofer ISE ()
Fraunhofer ISC ()
Fraunhofer IWM ()

The demand for transparent electrodes to be applied as electrical contacts for inorganic and organic light emitting diodes, solar cell and flat panel displays is strongly increasing due to the extensive market growth in these areas. The solutions available today only partially fulfil the demands on low resistivity, high transmittance, large area deposition, low cost manufacturing, ability for fine pattering, light scattering and precise alignment of the electronic structure to surrounding semiconductors and metals. The cooperation of five Fraunhofer institutes aimts towards achieving fundamental knowledge and control about the defect chemistry and morphology of the transparent semiconductive oxides to manufacture materials and devices with outstanding performances. Starting from the first principle material simulation using the density functional theory, we investigate into the effect structure of polycrystalline TCOs and TCO metal interfaces to identify relevant dopants for n-and p-type conductivity and the impact of the polycrystalline crystal structure on doping. The deposition of the TCO films is either by PVD or by Sol-Gel deposition. Using Sol-Gel we achieve transparent and conductive ZnO:Al films with resistivity of 1600 µcm as well as patterned ITO films by Sol-Gel printing of OLED manufacturing. Deposition of p-type conductive films by Sol-Gel on soda lime glass has been achieved by the first time for CuCrO2 and CuCr1-xAlx: Mg films. Sputter deposition of p-type CuCrO2 has shown to be successful using the novel technique of hollow cathode gas flow sputtering (GFS). The new method of high power pulse magnetron sputtering (HIPIMS) is used for the deposition of n-type TCOs with improved properties in terms of doping efficiency, ultra smooth surface morphology and excellent chemical durability. Magnetron sputtering of insulator-metal-insulator stacks (IMI) is utilized for low cost organic solar cell manufacturing where the adjustment of work unction and corrosion resistance is crucial for the performance of the device. Furthermore, we report in TCO development for Si based HIT solar cells and a-Si:H / c-Si:H tandem cells with improved light management and on OLEDs for lighting application using Ag or ZnO:Al based transparent conductors and printed TCOs.