Copper-Indium-Boron-Diselenide Absorber Materials
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1012-Y03-21
Copper-Indium-Boron-Diselenide Absorber Materials Natale J. Ianno1, Rodney J. Soukup1, Tobin Santero1, Chad Kamler1, James Huguenin-Love1, Scott A. Darveau2, Jiri Olejnicek2, and Christopher L. Exstrom2 1 Dept. of Elec. Eng., University of Nebraska-Lincoln, 209N WSEC, Lincoln, NE, 68588-0511 2 Dept. of Chemistry, University of Nebraska at Kearney, 905 West 25th Street, Kearney, NE, 68849-1150 ABSTRACT Attempts to fabricate new CuIn1-xBxSe2 (CIBS) and CuBSe2 (CBS) thin-film materials have been complicated by the formation of interfering crystallites and by the loss of boron from the magnetron sputtered precursor alloys during the selenization and annealing processes. Raman and Auger spectroscopic analysis as well as X-ray diffraction studies show that the formation of boron selenide may be contributing to the difficulty in creating these new materials.
INTRODUCTION While much progress has been made in photovoltaic cell development, the United States still does not have a cost-competitive version of a solar cell for domestic or industrial applications except in very remote areas of the country. In order for photovoltaic systems to be competitive, a 15% module efficiency with an installed efficiency of 12% at a cost of $1/Wp and a 20 year lifetime must be achieved. Broad-based U.S. government-supported research has determined that this goal can most likely be met by thin-film solar cells [1]. Of these thin film materials, the CuInSe2 (CIS) family shows the most promise [2]. Unfortunately, solar cells produced with CIS as the absorber layer are limited in efficiency as a consequence of the relatively small bandgap of 1.04 eV [3]. Ongoing research has been directed toward materials for which lighter elements from group IIIA of the periodic table are substituted in part for the indium in order to increase the bandgap. To date, the greatest energy conversion efficiency, 19.5%, has been achieved with a CuIn0.74Ga0.26Se2 (CIGS) absorber layer which has a bandgap of 1.15 eV with an open circuit output voltage of 0.701 V [4,5]. Changes in the bandgap structure limits the maximum amount of Ga that can be substituted and still allow the solar cell to maintain this higher efficiency. We are working toward the fabrication and study of a new material, copper indium boron diselenide, CuIn1-xBxSe2 (CIBS), which, to the best of our knowledge, has never been grown and studied. Boron should yield a higher bandgap, closer to the ideal value of 1.5 eV, for lower concentrations of boron than either gallium or aluminum [6]. We anticipate this lower concentration to lead to thin ordered films approaching the idealized chalcopyrite crystal structure of CIS. This material has not been studied because the excessively high boiling point of boron prevents its deposition by evaporation, the classical means of producing CIS-based solar cell films. Boron concentration in the films is a critical parameter in projecting what bandgaps may be achieved. Based on the results for Ga and Al substitution, [6] we have calculated that less than 2
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