Organics filled one-dimensional TiO2 nanowires array ultraviolet detector with enhanced photo-conductivity and dark-resistivity

Annealing effect on the physical properties of TiO2 thin films deposited by spray pyrolysis

Titanium dioxide (TiO2) thin films were deposited on glass substrates at 350 °C using the spray pyrolysis technique. As deposited and annealed thin films were characterized by X-ray diffraction, scanning electron microscopy, UV-VIS spectroscopy, and photodetection. Unlike the as deposited samples which were amorphous, annealed samples show an anatase phase. Films were absorbent in the UV region and the band gap energy decreases from 3.78 eV to 3.4 eV with annealing. The photoresponse of TiO2 photodetectors was recorded under UV (λ1 = 365 nm, λ2 = 254 nm) and visible light illumination by reversible switching (ON/OFF) cycles using DC electrical characterization. Photosensitive properties such as reproducible photosensitivity, responsivity, and detectivity were also studied.

Polypyrrole Film Deposited-TiO2 Nanorod Arrays for High Performance Ultraviolet Photodetectors

TiO2-based ultraviolet photodetectors have drawn great attention and are intensively explored. However, the construction of TiO2-based nanocomposites with excellent ultraviolet responses remains challenging. Herein, a TiO2 nanorod array was successfully prepared on fluorine-doped tin oxide (FTO) conductive glass by a one-step hydrothermal method. Then, polypyrrole (PPy)-TiO2 nanorod array composites were designed via subsequent in situ oxidative polymerization. The morphologies, structures, and photocurrent responses of the nanocomposites were systematically investigated. The results demonstrated that polypyrrole-TiO2 exhibited a stronger photocurrent response than pure TiO2 due to the p-n junction formed between n-type TiO2 nanorod arrays and p-type polypyrrole. The PPy-TiO2 composite obtained by deposition three times had the best photoelectric properties, exhibiting good performance with a sensitivity of 41.7 and responsivity of 3.5 × 10−3 A/W. Finally, the mechanism of the photoelectrical response of PPy-TiO2 composites was discussed, guiding the design of high-performance TiO2-based ultraviolet photodetectors.

Solution processed transparent anatase TiO2 nanoparticles/MoO3 nanostructures heterojunction: high performance self-powered UV detector for low-power and low-light applications

Ultraviolet (UV) photodetectors are considered as the major players in energy saving technology of the future. Efforts are needed to further develop such devices, which are capable of operating efficiently at low driving potential as well as with weak illumination. Herein, we report an all-oxide, highly transparent TiO2/MoO3 bilayer film, with nanoparticulate anatase TiO2 as the platform, fabricated by a simple solution based method and demonstrate its use in UV photodetection. Photoconductivity measurement with 352 nm light reveals the self-powered UV detection capability of the device due to the built-in potential at the bilayer interface. The device exhibits a high photoresponsivity (46.05 A W-1), detectivity (2.84 × 1012 Jones) and EQE (16 223%) even with a weak illumination of 76 μW cm-2, at a low bias of only -1 V. The self-powered performance of the bilayer device is comparable to that of commercial Si photodetectors as well as other such UV detectors reported based on metal oxide heterojunctions. The improved and faster photoresponse shown by the device is due to the formation of an effective heterojunction, as evidenced by XPS, electrochemical and I-V studies. It can be further attributed to the better charge transport through the densely aligned nanostructures, reduced recombination and the better mobility of anatase TiO2 nanoparticles. The performance is best-in-class and proves the potential of the transparent heterojunction to be used in highly responsive, self-powered UV detectors for low bias, low light applications.

Self-Powered and Broadband Lead-Free Inorganic Perovskite Photodetector with High Stability

Metal halide perovskite materials have opened up a great opportunity for high-performance optoelectronic devices owing to their extraordinary optoelectronic properties. More than lead halide ones, stable and nontoxic bismuth halide perovskites exhibit more promise in their future commercialization. In this work, we developed for the first time photodetectors based on full-inorganic Cs₃Bi₂I_9-xBr_x perovskites and modulate their performance by varying x in the composition systematically. Among those self-powered photodetectors, those based on Cs₃Bi₂I₆Br₃ shows the best performance with excellent photosensitivity of 4.1 × 10⁴ at zero bias as well as the responsivity and detectivity reaching 15 mA/W and 4.6 × 10¹¹ Jones, respectively. More strikingly, the full-inorganic perovskite photodetectors exhibit excellent stability in the ambient environment and can maintain over 96% of the initial value after 100 days owing to the high stability of the core perovskite film. The paper definitely paves an alternative and promising strategy for the design of future commercial photodetectors that are self-powered, stable, nontoxic, etc.

Position-controlled laser-induced creation of rutile TiO2 nanostructures

For potential applications of nanostructures, control over their position is important. In this report, we introduce two continuous wave laser-based lithography techniques which allow texturing thin TiO₂ films to create a fine rutile TiO₂ structure on silicon via spatially confined oxidation or a solid-liquid-solid phase transition, for initial layers, we use titanium and anatase TiO₂, respectively. A frequency-doubled Nd:YAG laser at a wavelength of 532 nm is employed for the lithography process and the samples are characterized with scanning electron microscopy. The local orientation of the created rutile crystals is determined by the spatial orientation of hydrothermally grown rutile TiO₂ nanorods. Depending on the technique, we obtain either randomly aligned or highly ordered nanorod ensembles. An additional chemically inert SiO₂ cover layer suppresses the chemical and electronic surface properties of TiO₂ and is removed locally with the laser treatment. Hence, the resulting texture provides a specific topography and crystal structure as well as a high contrast of surface properties on a nanoscale, including the position-controlled growth of TiO₂ nanorods.

Advanced scanning probe lithography using anatase-to-rutile transition to create localized TiO2 nanorods

In this article, we demonstrate the position-controlled hydrothermal growth of rutile TiO₂ nanorods using a new scanning probe lithography method in which a silicon tip, commonly used for atomic force microscopy, was pulled across an anatase TiO₂ film. This process scratches the film causing tiny anatase TiO₂ nanoparticles to form on the surface. According to previous reports, these anatase particles convert into rutile nanocrystals and provide the growth of rutile TiO₂ nanorods in well-defined areas. Due to the small tip radius, the resolution of this method is excellent and the method is quite inexpensive compared to electron-beam lithography and similar methods providing a position-controlled growth of semiconducting TiO₂ nanostructures.

Facilitated extrinsic majority carrier depletion and photogenerated exciton dissociation in an annealing-free ZnO:C photodetector

Applications of ZnO in photodetectors are limited by the great quantity of extrinsic majority carriers due to structural defects and difficult exciton dissociation due to the large exciton binding energy; these generally lead to a higher dark current (Id) and lower light current (Il), severely degrading the responsivity and detectivity. C dots are incorporated into an annealing-free ZnO layer to innovatively construct a local built-in electric field (Ebi) using the difference in the work functions; this simultaneously overcomes the drawbacks of the pristine ZnO photosensitive layer. In dark, the extrinsic majority carrier of ZnO is depleted around the incorporated C dots due to the self-depleting effect; thus, the Id decreases. Under UV illumination, the photogenerated exciton driven by the local Ebi is easily dissociated into a free charge carrier, contributing to the improved Il. This study paves a universal way to effectively improve the detection characteristics of photoconductive devices by incorporating the local Ebi.