A modified spray pyrolysis technique is used for preparing α‐MoO3 thin films after subsequent heat treatment at a relatively low temperature. The spray parameters are selected through a wide variety of elaboration conditions for best photochromic features. Different numbers of spraying and drying cycles are performed to investigate the thickness effect on the structural, morphological, optical, electrical, and photo‐electrical properties of the nanostructured α‐MoO3 films. These film samples are characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), and thus the film thickness effect is elucidated and correlated to the crystallite shape and size. The SEM micrographs show fibrous‐reticulated morphology for all the film samples investigated here. The photochromic properties of α‐MoO3 sprayed thin films are investigated by measuring the transmission spectra before and after UV‐light exposure. The changes in the optical transmission of these film samples are monitored for different exposure times. The UV exposure time effect as well as the thickness effect on the photochromic response of the film samples is investigated and discussed based on the particle size analysis. The photosensitivity is evaluated in various illumination levels to elucidate the carrier transport in the α‐MoO3 films and to determine the type of the recombination processes in these films.

In the current study, α-MoO3 nanocrystals were successfully synthesized from ammonium heptamolybdate tetrahydrate using a simple hydrothermal route. The influence of calcination temperature on the structural, optical and electrical properties was systematically investigated for the MoO3 powder products. The XRD results were analyzed for these powders, revealing the formation of a mixed phase (β- and α-MoO3) at calcination temperatures ranging from 350 °C–450 °C, and hence a residual monoclinic phase still exists in the samples at the calcination temperature of 450 °C. Subsequently, the mixed phase was completely converted to a pure single phase of α-MoO3 at a calcination temperature of 500 °C. The optical properties of the MoO3 powders were investigated using the transformed diffuse reflectance technique according to Kubelka–Munk theory. For such a powder product, the results of the optical measurements demonstrated the realization of indirect and direct allowed transitions at the spectral ranges 3.31–3.91 eV and 3.66–4.27 eV, respectively. The indirect- and direct-allowed band-gaps of the MoO3 products were found to increase from 2.69–3.12 eV and from 3.43–3.64 eV, respectively, by increasing the calcination temperature from 350 °C–600 °C. The MoO3 powders calcined at different temperatures were converted into five dense tablets for performing the electrical measurements. These measurements were carried out at different working temperatures using a system operating under high vacuum conditions. The results revealed that the dc-conductivity of such a tablet typically increases by more than five orders of magnitude with an increase in the working temperature from 77–300 K. These results also demonstrated a high dependence of dc-conductivity on the calcination temperature for the MoO3 products. The dc-conductivity as a function of the operating temperature revealed the presence of at least three different electrical conduction mechanisms for the same MoO3 tablet.

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