Photochromic Response and Steady‐State Photoconductivity of Fibrous‐Reticulated α‐MoO₃ Thin Films Prepared by Modified Spray Pyrolysis Technique

Abstract

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.

Major role of intrinsic defects in optical and electrical properties adopting a highly defect-controlled photoconductivity in spin-coated α-MoO3 thin films gained after UV illumination

“…Similar behavior has been reported in the literature [16,26], whereas MoO 3 thin films have been prepared by a carbonyl chemical vapor deposition process at atmospheric pressure [16] and by sol-gel dip coating technique [26]. Nevertheless, the bandgap values of the film samples are inconsistent with those reported by Gesheva et al [16] and Chibane et al [26]. However, the inconsistency between these data is mainly due to the variety of the starting materials used, the deposition techniques utilized, and the preparation conditions applied [33].…”

“…This is well consistent with the experimental observations stated in view of the XRD results, whereas the increase in the LTT temperature promotes crystallinity and consequently enlarge crystallite size that results in a reduction in the oxygen vacancies. Similar observations have been previously reported for α-MoO 3 thin films by Gesheva et al [16] and Chibane et al [26]. But further increase in the LTT temperature up to 625 °C significantly influences the optical properties of the produced α-MoO 3 film samples, making them with high transparency (i.e.…”

“…Whereas, the density of oxygen vacancies as structural defects is expected to be abruptly reduced within the well crystallized film samples. Similar behavior has been reported in the literature [16,26], whereas MoO 3 thin films have been prepared by a carbonyl chemical vapor deposition process at atmospheric pressure [16] and by sol-gel dip coating technique [26]. Nevertheless, the bandgap values of the film samples are inconsistent with those reported by Gesheva et al [16] and Chibane et al [26].…”

“…Furthermore, molybdenum trioxide has been widely studied a high chemically stable oxide for finding application in sensing [11], catalysis [12] and lithium-ion battery [13]. Many different deposition techniques have been developed to prepare α-MoO 3 thin films, including DC magnetron sputtering [14], laser thermal evaporation technique [15], carbonyl chemical vapor deposition [16], spray pyrolysis technique [17,18], sol-gel dip-coating [19], and spin-coating technique [20]. Amongst these techniques, the sol-gel based techniques (i.e.…”

Controlled optoelectronic properties and abrupt change in photosensitivity by suppressing density of oxygen vacancies in SnO2 nanocrystalline thin films prepared at various spray-deposition temperatures

“…The reactor of this technique was designed to be composed of a galvanized chamber, and this safety enclosure was attached to a separate control box to control the spray parameters. More details concerning this technique can be found in our previous work [35]. A long optimization process was performed for the MCSP technique, and thus the values of the spray deposition parameters were selected through a wide variety of elaboration conditions.…”