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Materials 2016, 9(1), 63; doi:10.3390/ma9010063

Influence of Oxygen Concentration on the Performance of Ultra-Thin RF Magnetron Sputter Deposited Indium Tin Oxide Films as a Top Electrode for Photovoltaic Devices

1
Department of Materials Science & Engineering, Michigan Technological University, 1400 Townsend, Houghton, MI 49931, USA
2
Department of Materials Science, School of Chemistry, Madurai Kamaraj University, Ta mil Nadu, Madurai 625 019, India
3
Department of Electrical & Computer Engineering, Michigan Technological University, 1400 Townsend, Houghton, MI 49931, USA
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editor: Lioz Etgar
Received: 17 December 2015 / Revised: 6 January 2016 / Accepted: 14 January 2016 / Published: 20 January 2016
(This article belongs to the Special Issue Photovoltaic Materials and Electronic Devices)
View Full-Text   |   Download PDF [2572 KB, uploaded 20 January 2016]   |  

Abstract

The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivity and high transmittances in the visible range of the electromagnetic spectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methods has presented a number of challenges; however, a novel method involving chemical shaving of thicker (greater than 80 nm) RF sputter deposited high-quality ITO films has been demonstrated. This study investigates the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films to provide a detailed understanding of the interaction of all critical experimental parameters to help create even thinner layers to allow for more finely tune plasmonic resonances. ITO films were deposited on silicon substrates with a 98-nm, thermally grown oxide using RF magnetron sputtering with oxygen concentrations of 0, 0.4 and 1.0 sccm and annealed at 300 °C air ambient. Then the films were etched using a combination of water and hydrochloric and nitric acids for 1, 3, 5 and 8 min at room temperature. In-between each etching process cycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy, 4-point probe (electrical conductivity), and variable angle spectroscopic ellipsometry. All the films were polycrystalline in nature and highly oriented along the (222) reflection. Ultra-thin ITO films with record low resistivity values (as low as 5.83 × 10−4 Ω·cm) were obtained and high optical transparency is exhibited in the 300–1000 nm wavelength region for all the ITO films. The etch rate, preferred crystal lattice growth plane, d-spacing and lattice distortion were also observed to be highly dependent on the nature of growth environment for RF sputter deposited ITO films. The structural, electrical, and optical properties of the ITO films are discussed with respect to the oxygen ambient nature and etching time in detail to provide guidance for plasmonic enhanced a-Si:H solar PV cell fabrication. View Full-Text
Keywords: transparent conducting oxide; indium tin oxide; plasmonics; wet etching; photovoltaics; optics transparent conducting oxide; indium tin oxide; plasmonics; wet etching; photovoltaics; optics
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Gwamuri, J.; Marikkannan, M.; Mayandi, J.; Bowen, P.K.; Pearce, J.M. Influence of Oxygen Concentration on the Performance of Ultra-Thin RF Magnetron Sputter Deposited Indium Tin Oxide Films as a Top Electrode for Photovoltaic Devices. Materials 2016, 9, 63.

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