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In this paper we focus on indium oxide and indium iron oxide as an alloy to fabricate a protective thin film (transparent, conductive, and corrosion resistant; TCCR) for amorphous silicon-based solar cells, which can be used in immersion-type photoelectrochemical cells for hydrogen production. From the work completed, the results indicate that samples made at 250
C with indium and indium iron oxide targets powered at 30 and 100 W, respectively, and a sputter deposition time of 90 min produced optimal results when deposited directly on single-junction amorphous silicon solar cells. At 0.65 V (versus SCE), the best sample conditions display a maximum current density of 21.4 mA/cm2. I. INTRODUCTION

This project focuses on using indium oxide and indium iron oxide to make a protective thin film (transparent, conductive, and corrosion resistant; TCCR) to deposit on top of amorphous silicon-based solar cells.1–5 TCCR-coated amorphous silicon (a-Si) solar cells are used for hydrogen production in immersion-type photoelectrochemical (PEC) cells as schematically shown in Fig. 1.6 The stack in the immersion-type PEC is shown in Fig. 2. In this work we focus on the topmost layer. The rest of the layers are mature research that has been thoroughly investigated.7,8 The results indicate that TCCR samples made at 250
C for 90 min deposition time, with indium and indium iron oxide targets powered at 30 and 100 W, respectively, sputter coated onto amorphous silicon solar cells produce optimal results. Indium oxide has ideal characteristics to act as a TCCR layer in hybrid photoelectrodes with a-Si solar cells. For a TCCR layer on a-Si solar cells, the standard conditions are that the protective top layer needs to be at least 90% transparent, that the layer needs to be conductive at 7 mA/cm2 or greater at 1.7 V (maximum power point voltage for a-Si), and that it must be corrosion resistant for thousands of hours. Additionally, the top layer material typically needs to be a wide band gap material and beyond the spectral response region of the a-Si solar cell. In2O3 and InFe2O4 are both wide band gap semiconductors that electronically mismatch with the top layer of the a-Si solar cell; thus both are ideal for TCCR materials. The oxide coating is conductive and does not interact in the semiconductor band struca)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0010 J. Mater. Res., Vol. 25, No. 1, Jan 2010

http://journals.cambridge.org

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ture of the a-Si solar cell. Pure In2O3 has rather poor stability in basic electrolyte so it needs to be alloyed to a compound that can stabilize the film, and the films need to be deposited at low temperatures (under 270
C) so that the a-Si:H bonds will not degrade during In2O3–InFe2O4 deposition. These thin films were created using radiofrequency (rf) sputter deposition. Two 2 in. sputter guns were used with respective targets of indium and indium iron oxide. The three main variables considered were the temperature of t