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

Abstract

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 [110]-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.