CuInS 2 /PEDOT Photovoltaic Structure
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CuInS2/PEDOT Photovoltaic Structure Sergei Bereznev*, Igor Konovalov1, Julia Kois, Enn Mellikov and Andres Öpik Tallinn Technical University, Department of Material Science, Ehitajate tee 5, 19086 Tallinn, Estonia. Phone +372 6202820, Fax +372 6202798, E-mail: [email protected] *Corresponding author 1 Universität Leipzig, Wilhelm Ostwald Institute for Physical and Theoretical Chemistry, Linnéstr. 2, 04103 Leipzig, Germany ABSTRACT Structures based on combination of electrically conductive polymers with inorganic semiconductors are currently intensively investigated with the aim to prepare low-cost, largearea and flexible photovoltaic devices. In this study, multilayer structures consisting of CuInS2 (CIS) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS) thin films were prepared and investigated for photovoltaic applications. Polycrystalline CIS absorber layers were synthesized on top of a layered structure on Cu tape substrate using socalled non-vacuum CISCuT technique. Thin PEDOT buffer layers doped with PSS were deposited onto KCN etched and vacuum annealed CIS films. The deposition was performed using the spin-casting technique from an aqueous dispersion of PEDOT/PSS mixed with Nmethylpyrrolidone, isopropanol, glycerin and epoxysilane additives. Optimal deposition parameters for stable PEDOT films with a good adherence to the surface of CIS were selected experimentally. The morphology and thickness of prepared films and structures was determined using SEM technique. Average film thickness was about of 1.5 µm for CIS and 50 nm for PEDOT films. Current-voltage and impedance characteristics were measured. Significant photovoltage and photocurrent of the photovoltaic structures were observed under standard illumination intensity. The best structure showed an open-circuit voltage of 510 mV and a shortcircuit current density of 20.2 mA/cm2.
INTRODUCTION CuInS2 (CIS) and CuInSe2 (CISe) are direct-gap polycrystalline semiconductors with very high optical absorption coefficients of more than 104 cm-1 and they are presently being extensively studied for application in solar cells. Energy band gap, adjustable between about 0.9 and 1.6 eV by composition and well adapted to the solar spectrum, high stability and easy p- and n-type dopability are also important reasons for this [1-3]. In present work so-called CISCuT deposition method was applied for the formation of polycrystalline CIS absorber layers on copper tape [3]. Electrically conductive polymers (ECP) are a novel class of conductive materials which combine optical and electrical properties of semiconductors with processing advantages, good mechanical properties and low cost of polymers. ECP present new possibilities of producing coatings that function as an integral part of electronic devices, e.g. solar cells, to produce electricity from sunlight [4,5]. Combination of CIS with ECP, e.g. polypyrrole (PPy) or poly(3,4ethylenedioxythiophene) (PEDOT) is attractive for use in thin-film photovoltaic cell structures.
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