Nickel Oxide Films Deposited by Sol-Gel Method: Effect of Annealing Temperature on Structural, Optical, and Electrical Properties

Tatyana Ivanova; Antoaneta Harizanova; Maria Shipochka; Petko Vitanov

doi:10.3390/ma15051742

Nickel Oxide Films Deposited by Sol-Gel Method: Effect of Annealing Temperature on Structural, Optical, and Electrical Properties

Materials (Basel). 2022 Feb 25;15(5):1742. doi: 10.3390/ma15051742.

Authors

Tatyana Ivanova¹, Antoaneta Harizanova¹, Maria Shipochka², Petko Vitanov¹

Affiliations

¹ Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, Tzarigradsko Chaussee 72, 1784 Sofia, Bulgaria.
² Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G, Bonchev St., bl. 11, 1113 Sofia, Bulgaria.

Abstract

In our study, transparent and conductive films of NiO_x were successfully deposited by sol-gel technology. NiO_x films were obtained by spin coating on glass and Si substrates. The vibrational, optical, and electrical properties were studied as a function of the annealing temperatures from 200 to 500 °C. X-ray Photoelectron (XPS) spectroscopy revealed that NiO was formed at the annealing temperature of 400 °C and showed the presence of Ni⁺ states. The optical transparency of the films reached 90% in the visible range for 200 °C treated samples, and it was reduced to 76-78% after high-temperature annealing at 500 °C. The optical band gap of NiOx films was decreased with thermal treatments and the values were in the range of 3.92-3.68 eV. NiO_x thin films have good p-type electrical conductivity with a specific resistivity of about 4.8 × 10^-3 Ω·cm. This makes these layers suitable for use as wideband semiconductors and as a hole transport layer (HTL) in transparent solar cells.

Keywords: NiO; electrical properties; optical properties; sol-gel technology; thin films.