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The optical and photoelectrochemical (PEC) properties of semiconductors can be manipulated by varying the deposition time and the solvent used. In this work, the study investigates the influence of organic solvent (methanol and ethanol) on accelerating deposition time for the efficient optical and photoelectrochemical performance of the fabricated α-Fe2O3 thin film photoanode below 10 minutes. The α-Fe2O3 film was fabricated via aerosol-assisted chemical vapor deposition (AACVD). The study discovered that the solvent with high polarity enhanced the crystal growth direction of α-Fe2O3 on the (110) orientation. The UV-vis showed that all deposited α-Fe2O3 films exhibit the absorption band in the visible-light region with the estimated energy bandgap of 2.10 eV. Furthermore, the PEC performance exhibited good photoanodic responses with excellent charge transfer behavior and photostability. These findings show that the choice of solvent could influence the rapid deposition time, thus, would be reliable to accelerate the fabrication process of photoelectrochemical water-splitting photoanode.

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).

Aerosol-assisted chemical vapour deposition (AACVD) is capable of producing WO3 film with good optical and electrical properties for photoelectrochemical (PEC) water splitting. However, the conventional AACVD method is time-consuming because post-annealing treatment is usually required after WO3 film was deposited under nitrogen flow. Therefore, we omitted the post-annealing treatment by employing purified air as carrier gas (known as one-step) instead of nitrogen (known as two-step) which decreases the fabrication time by 13-fold. One-step WO3 also shows improved charge separation and PEC reaction due to the coexistence of (002), (020) and (200) facets and higher oxygen vacancies. Further optimization using acetone/ethanol as solvent, 10 min deposition time and 450°C deposition temperature leads to photocurrent density of 0.32 mA cm-2 at 1.23 VRHE, which is the highest performance reported for AACVD-based WO3 photoanode. The development of rapid and industrially applicable deposition method would pave the way for real practice of PEC technology.

The electron transport layer (ETL) plays a pivotal role in polymer solar cell (PSC) for improving the efficiency. TiO2 is widely used as ETL, but it has low electron mobility and poor conductivity. Here, we demonstrated the incorporation of the novel γ-radiated g-C3N4 additive into the TiO2-based ETL polymer solar cell. The γ-radiated g-C3N4 tunes the surface morphology of the ETL into smoother and denser film relatively than the reference film. The γ-radiated g-C3N4 modified ETL also shows improved charge transfer properties. As a result, the device with modified ETL containing γ-radiated g-C3N4 additives shows a double enhancement of PCE with respect to the reference device.

Perovskite solar cells (PSC) are currently experiencing rapid development due to the potential for achieving high efficiency but the fabrication process is strictly restricted inside an inert environment. This is because high relative humidity (RH) condition may cause irreversible degradation or low quality of perovskite film. Since the film quality and device performance depend strongly on the deposition protocol, a systematic investigation about the impact of one-step and two-step spin coating on perovskite film prepared in high-humidity is needed. Hereby, we developed PSC in humid atmosphere (RH40-50%) using both deposition techniques to find the most easily-adopted coating method for PSC fabrication in high-humidity. Results show that one-step-based sample has numerous pinholes and smaller grain size whereas two-step-based counterpart exhibits compact surface coverage and large grains. Hence, the two-step-based film has higher light absorption, better charge transfer and lower charge recombination. The employment of PCBM as a secondary electron transport layer underneath the perovskite layer in one-step-based sample causes both layers to be washed away by chlorobenzene anti-solvent. However, such undesirable phenomenon is not seen for the two-step-based sample. Therefore, the use of two-step method is strongly recommended for the development of efficient PSC in open atmosphere without humidity restriction.

The topology of electron density is a sketch that gives a clear picture about electronic distribution and details information of natural molecular bonding. In quantum mechanics or particularly in quantum chemistry, the electron density is a measure of the probability of an electron occupying at any infinitesimal element of space surrounding at any given point.Studies about the topology of electron density in Cd0.5Zn0.5S at plane (101) were conducted by the application of density functional theory (DFT) within linear augmented plane wave (LAPW) by using the WIEN2k software. In this calculation, generalized gradient approximation (GGA) methods were used to calculate the exchange-correlation potential of the electrons. Based on this calculation, the topology of electron density were presented in a contour plot (2D) and also inarelief map plot (3D) in order to see the way electron density, ρ of Cd0.5Zn0.5S defines the gradient field and hence the bonding type. From these plots, we identified the bond paths that coincide with the contours of electron to suggest that Cd0.5Zn0.5S exhibited characteristics of covalent and a slightly ionic bond character.