Temperature optimization of NiO hole transport layer prepared by atomic layer deposition

Atomic layer deposited (ALD) nickel oxide (NiO) thin film is frequently utilized as a hole transport layer (HTL) for perovskite solar cells (PSCs). Particularly nickel(II) 1-dimethylamino-2-methyl-2-butoxide (Ni(dmamb)2) precursor and ozone reactant are used for NiO film deposition. The substrate temperature effect on the stoichiometric composition for oxygen vacancies defects and electrical properties such as mobility is crucial, affecting further device performance. In the present study, NiO thin films are grown using the ALD method at a substrate temperature range between 180 to 250 °C on SiO2/Si substrates. Next, the effect of substrate temperature on the film composition, valence levels, nickel oxidation states, oxygen vacancies, and electrical properties was systematically examined, not to mention film growth, thickness, morphology, crystallinity, and optical properties. At 180 °C, the film growth rate was 0.017 nm/cycle, which was increased to 0.025 nm/cycle at 250 °C. All grown NiO films exhibited polycrystalline cubic crystal orientation, and the (200) plane simultaneously Ni3+ phase coexists with the Ni2+ phase. Furthermore, the electrical resistivity and mobility increased from 2.36 – 3.24 × 102 Ω.cm and 9.6–21.9 cm2V−1s−1 with substrate temperatures of 180 °C–230 °C. The prepared NiO films were optically transparent, >70% in the visible region, and the Ultraviolet photoelectron spectroscopy (UPS) study revealed that the variation in the valance band and conduction bands critically depended on the growth temperature. Thus, our findings reveal that the chemical and electrical characteristics of deposited NiO thin film are precisely influenced by substrate temperature; it will also offer considerable promise for developing NiO HTL concerning PSCs device improvement.