Rapid Processing of In-Doped ZnO by Spray Pyrolysis from Environment-Friendly Precursor Solutions

Nina Winkler,Theodoros Dimopoulos,Emil List-Kratochvil,Wolfgang Kautek,Adhi Wibowo,Bernhard Kubicek,Giovanni Ligorio

doi:10.3390/coatings9040245

Nina Winkler, Theodoros Dimopoulos + Show 5 more

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https://doi.org/10.3390/coatings9040245

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Abstract

This study focused on the deposition of indium-doped zinc oxide (IZO) films at high growth rates by ultrasonic spray pyrolysis. We investigated the influence of processing parameters, such as temperature and solution flow rate, on the structural, optical, and electrical film properties. For all depositions, low-cost and low-toxicity aqueous solutions and metal salt precursors were used. Through the optimization of the spraying parameters and pattern, a spatially homogeneous IZO layer with transparency greater than 80%, resistivity of 3.82 × 10−3 Ω·cm for a thickness of 1800 nm (sheet resistance of 21.2 Ω/sq), Hall carrier density of 1.36 × 1020 cm−3, Hall mobility of 12.01 cm2 V−1 s−1, and work function of 4.4 eV was obtained. These films are suitable for implementation in optoelectronic and photovoltaic devices.

Highlights

Transparent conducting oxides (TCOs) are important materials for various applications, such as flat-panel displays [1], functional windows [2], light-emitting diodes [3], and photovoltaics [4].Established TCOs are wide-band gap (>3 eV), n-type semiconductors based on indium oxide (In2 O3 ), tin oxide (SnO2 ), or zinc oxide (ZnO) that have been doped with donors to increase the charge carrier concentration
Borosilicate glass substrates (Schott Nexterion®D, Mainz, Germany. 7.5 × 2.5 cm2 ) were prepared as previously reported [13]. They were ultrasonically cleaned in a Hellmanex®III (Munich, Germany) washing solution, rinsed with deionized water (DI, 18 MΩ·cm−1 ) and isopropanol, and dried in nitrogen stream
The solution composition influences the properties of the films prepared by spray pyrolysis in various ways [15,16]

Summary

Introduction

Established TCOs are wide-band gap (>3 eV), n-type semiconductors based on indium oxide (In2 O3 ), tin oxide (SnO2 ), or zinc oxide (ZnO) that have been doped with donors to increase the charge carrier concentration. ZnO-based TCOs are especially attractive due to their low cost and ease of fabrication through solution-based deposition techniques. To attain a high carrier concentration and improve the film conductivity, ZnO can be doped with the group III elements Al, Ga, or In. Depending on the deposition methods and conditions, different dopants result in distinctive film properties. For spray pyrolysis—a versatile and low-cost solution-based deposition technique—it was shown that doping with In promotes lower film resistivity compared to Al or Ga, even at low In concentrations [5,6,7]

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