One-pot hydrothermal synthesis of orientated delafossite CuFeO2 films from a mildly acidic solution on substrates

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2023-06, Vol.11 (25), p.8616-8625
• Main Authors: Shinagawa, Tsutomu, Tachibori, Wataru, Nishii, Tomoya, Ohtaka, Atsushi
• Format: Article
• Language: English
• Subjects: Acidic oxides; Aqueous solutions; Copper; Copper chloride; Crystallization; Energy conversion; Fluorine; Glass substrates; Hydrothermal reactions; Infrared spectroscopy; Iron chlorides; Iron sulfates; Low temperature; Optoelectronics; Oxide coatings; Photoelectrons; Preferred orientation; Raman spectroscopy; Reaction time; Spectrum analysis; Thickness; Tin oxides
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d3tc01300f

Ternary Cu(i)-based oxides are among the most promising optoelectronic materials for energy-conversion applications, but the development of ternary Cu(i)-based oxide films from solutions at low temperatures is a challenging task. Here we report the low-temperature and short-time hydrothermal formation of delafossite CuFeO2 films with a [1120]-preferred orientation on fluorine-doped tin oxide (FTO) glass substrates. Well-crystallised p-type CuFeO2 films with a thickness of ∼2.1 μm and a bandgap energy of 1.48 eV were obtained via hydrothermal reaction at 150 °C for 1 h in weakly acidic aqueous solutions containing CuSO4, FeSO4 and urea. The growth of CuFeO2 under different hydrothermal conditions—reaction times (15 min–40 h), reaction temperatures (100–180 °C) and metal salts (CuSO4, Cu(NO3)2, CuCl2, Cu(OAc)2, FeSO4 and FeCl2)—was characterised using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, IR spectroscopy and X-ray photoelectron spectroscopy. Well-crystallised CuFeO2 films were formed under the following conditions: reaction time of ≥1 h, reaction temperature of ≥150 °C and a sulphate system of CuSO4 and FeSO4.