Temperature‐Driven Perturbations in Growth Kinetics, Structural and Optical Properties of NiO Thin Films

Abstract

Recent years have witnessed a growing demand in the improvement of nanostructured metal oxides with p-type conductivity. Nickel oxide (NiO) is a naturally grown p-type metal-oxide semiconductor pursuing direct wide bandgap (from 3.6 to 4 eV), moderate conductivity, good chemical stability, high transmittance, and excellent optoelectronic properties. [1] It crystallizes in sodium chloride (NaCl)-type face-centered cubic (FCC) structure and exhibits maximum hole conductivity along (111) direction. [1][2][3] Being a transparent p-type semiconducting oxide, NiO offers potential application in the domain of perovskite solar cells (transparent electrodes), visible blind photodetection, solid-state gas sensing and electrochromic displays, etc. [2][3][4][5] Despite its technological importance, the growth of device-grade NiO thin films has remained a challenging task, mainly attributed to its low conductivity. To date, numerous studies on the growth of NiO via various physical and chemical methods including magnetron sputtering, [6,7] plasma-enhanced chemical vapor deposition (PECVD), [8] pulsed laser deposition (PLD), [9] thermal evaporation, [10] spray pyrolysis, [11] sol-gel processing, [12] etc. have been reported so far. However, among the various aforementioned methods, radio-frequency (RF) magnetron sputtering is the most common and a widely used technique for the growth of NiO thin films. [13][14][15][16][17][18] Literature reports that growth parameters play a critical role in governing the properties of NiO films grown by RF magnetron sputtering. [13][14][15][16]19] Modifications in growth parameters may introduce various defects such as structural points defects, dislocations, or perturbation-induced ingap states, [13,15] affecting the structural, optical, and electrical properties of the grown NiO films. Ahmed et al. [16] observed that the growth of NiO is substrate dependent and that the inherent material properties depend strongly on the types of substrate (Si, GaAs, PET, etc). In contrast, Grilli et al. [19] reported that RF power and sputtering gas significantly influence the resistivity (from 10 À2 to 10 À1 Ω-cm) and transmittance of the grown NiO films. A recent study by Turgut et al. [20] said that oxygen partial pressure not only changes the structural and morphological properties, but it also influences the oxidation state of nickel, leading to significant variation in the performance of NiO-based hydrogen sensors. [20] In a recent report, Dhull et al. [21] also demonstrated that substrate temperature can play a significant role in tailoring the morphology of NiO films, leading to perturbation in charge transfer characteristics. However, few other studies were also conducted to explore the influence of growth temperature on structural, optical, morphological, and device applications of NiO thin films, but the extent of study was limited to a lower growth temperature, that is, up to 300 C only. [22][23][24][25] It implies that growth temperature significantly

Hollow Ni/NiO/C composite derived from metal-organic frameworks as a high-efficiency electrocatalyst for the hydrogen evolution reaction

“…Because the intensity of 1P LO and 2P LO was related to the defect states associated with Ni vacancies [55,56]. According to Mishra et al, the increased temperature reduces the Ni vacancies [57], which dominates the intensity of 1P LO [58]. Therefore, the high intensity of 1P LO could be ascribed to a large number of Ni vacancies in H-Ni/ NiO/C, which was formed at 250 °C.…”

Present Status and Future Perspective of Antimony Chalcogenide (Sb2X3) Photovoltaics

“…Inorganic HTMs have the advantages of high intrinsic stability and hole conductivity, in comparison to organic counterparts. Inorganic HTLs such as NiO, Cu 2 O, CuO, CuS, CuI, MnS, CuCrO 2 , CuGaO 2 , MoO 3 (as an interlayer), CuSCN, VO x , and WO x are inexpensive, abundant, and nontoxic and exhibit suitable band alignment for hole extraction. Due to the high hole mobility, good transparency, and stability, CuSCN has been considered as a potential HTL in Sb 2 X 3 solar cells .…”