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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.

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.

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.