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3-dimensional (3D) nanostructures have gained broad attention in the field of microelectronics and nanotechnology owing to their fascinating properties and potential for novel applications. To enable successful fabrication of the nanostructure, deep understanding on their growth mechanism is an absolute prerequisite. In this study, thin film of hematite (α-Fe2O3) nanoflakes is successfully converted to nanoflowers using aerosol-assisted chemical vapour deposition (AACVD) technique simply by supplying high amount of oxygen and regulating the deposition time. The crystal structure and morphological properties including thickness and roughness of the film are thoroughly investigated to provide a clear explanation on the growth mechanism of α-Fe2O3 by AACVD. Results indicate that (110) crystal plane is the predominant factor that influence the formation of nanoflowers with unique pyramidal nanostructure. This structure causes the film thickness to increase linearly while the surface roughness shows a logarithmic growth trend. The samples are further employed in photoelectrochemical (PEC) water splitting as photoanode where 40 min deposition period is the optimum condition for achieving PEC photocurrent density of up to 585 μA/cm2 at 1.2 V vs. Ag/AgCl. The major contributor towards the performance enhancement is the large surface area and high light absorption of α-Fe2O3 nanoflowers as this parameter provides greater sites for photocatalytic activity, greater charge generation and enhanced charge carrier separation efficiency.

In this study, g-C3N4 was synthesized from urea and then was fabricated into thin films using spin-coating followed by post- annealing in the temperature range of 150 °C–500 °C. Use of methanol rather than water as the solvent for preparation of the spin coating suspension proved to be beneficial. The chemical bond structure, morphology, and optical properties of g-C3N4 thin films depend on the post-annealing temperature. Post annealing at 350 °C is the optimum temperature, manifested by a strong/sharp intensity peak of triazine and C N bond in the g-C3N4 network by FT-IR. The average roughness (sa) of the g-C3N4 thin film decreased with increasing temperatures due to the decomposition occurring on the polymeric g-C3N4 thin film. Post annealing in the temperature range of 150 °C to 350 °C shows a reduction in the energy band gap from 2.79 eV to 2.71 eV, however annealing at higher temperatures (350 °C to 500 °C) resulted in larger energy band gaps of ~2.71 eV to 2.85 eV. After optimization of the post annealing temperature, the photocurrent density reached the value of ~20.73 μA cm−2 at 1.23 V versus Ag/AgCl in 0.5 M Na2SO4 electrolyte solution (pH 7).

In the present work, the redox behavior of vanadate ion in deep eutectic solvent (DES) was studied via cyclic voltammetry (CV) method where glyceline DES and NH4VO3 were used as electrolyte and the source of + 5 vanadium ions respectively. The CV showed a quasi-reversible redox couple pattern of + 5 to + 4 vanadium ions in glyceline DES. Analysis by UV-Vis revealed the presence of + 3 vanadium ions at λmax 545 nm. The glyceline DES does not only act as a solvent but also as a reducing agent by chemically reducing + 4 vanadium ions to the most stable oxidation state of + 3. Temperature dependence study of vanadate ion in glyceline DES showed that the peak current increased with temperature which enhances the reaction kinetics. In addition, the conductivity of NH4VO3 in glyceline DES improved remarkably with temperature, whereas its viscosity declined. Moreover, the Rs and Rct values decreased with increasing temperature.

The silicon heterojunction solar cell (SHJ) is considered the dominant state-of-the-art silicon solar cell technology due to its excellent passivation quality and high efficiency. However, SHJ’s light management performance is limited by its narrow optical absorption in long-wave near-infrared (NIR) due to the front, and back tin-doped indium oxide (ITO) layer’s free carrier absorption and reflection losses. Despite the light-trapping efficiency (LTE) schemes adopted by SHJ in terms of back surface texturing, the previous investigations highlighted the ITO layer as a reason for an essential long-wavelength light loss mechanism in SHJ solar cells. In this study, we propose the use of Molybdenum disulfide (MoS2) as a way of improving back-reflection in SHJ. The text presents simulations of the optical response in the backside of the SHJ applying the Monte-Carlo raytracing method with a web-based Sunsolve high-precision raytracing tool. The solar cells’ electrical parameters were also resolved using the standard electrical equivalent circuit model provided by Sunsolve. The proposed structure geometry slightly improved the SHJ cell optical current density by ~0.37% (rel.), and hence efficiency (η) by about 0.4% (rel.). The SHJ cell efficiency improved by 21.68% after applying thinner back ITO of about 30 nm overlayed on ~1 nm MoS2. The efficiency improvement following the application of MoS2 is tentatively attributed to the increased NIR absorption in the silicon bulk due to the light constructive interface with the backside components, namely silver (Ag) and ITO. Study outcomes showed that improved SHJ efficiency could be further optimized by addressing front cell components, mainly front ITO and MoS2 contact engineering.

Bismuth vanadate (BiVO4) is one of the n-type semiconductors which has attracted attention as one of the promising photoanodes semiconductor for photoelectrochemical water splitting due to its small optical band gap, low cost, negative conduction band edge and good stability. In this work, BiVO4 thin films is fabricated by using electrodeposition method and the XRD spectra reveal that the sample crystallizes in monoclinic scheelite type. The optical bands show the bandgap energy of BiVO4 thin films is 2.40 eV as determined by Tauc plot and exhibits an anodic photocurrent. Further study is focusing on determination of the conduction band (CB) and valence band (VB) of BiVO4 thin films which is derived experimentally by using XPS analysis, Mott–Schottky plot and Cyclic Voltammetry (CV) technique. Based on the results, it is found that different analysis techniques exhibit almost similar values of CB and VB of BiVO4 thin films. All techniques give VB maximum in the range of 2.02 eV–2.05 eV and CB minimum in the range of −0.35 eV to −0.39 eV. However, the flat-band potential determined from Mott–Schottky plot is nearly 0.1 eV from CB potential caused by the presence of Fermi level and the effect of Helmholtz capacitance for dielectric semiconductors. These findings clearly show that the experimental values of different analysis techniques give comprehensive approach to understanding the energy band structure of the BiVO4 thin films.