ABSTRACT
Flexible zinc oxide (ZnO) nanorod (NR) ultraviolet (UV)/gas dual sensors using silver (Ag) nanoparticle (NP) templates were successfully fabricated on a polyimide substrate with nickel electrodes. Arrays of Ag NPs were used as a template for the growth of ZnO NRs, which could enhance the flexibility and the sensing properties of the devices through the localized surface plasmon resonance (LSPR) effect. The Ag NPs were fabricated by the rapid thermal annealing process of Ag thin films, and ZnO NRs were grown on Ag NPs to maximize the surface area and form networks with rod-to-rod contacts. Because of the LSPR effect by Ag NPs, the UV photoresponse of the ZnO NRs was amplified and the depletion region of ZnO NRs was formed quickly because of the Schottky contact with the Ag NPs. As a consequence, ZnO NR UV/gas dual sensors grown on the Ag NP template with a diameter of 28 nm exhibited the outstanding UV-sensing characteristics with a UV on-off ratio of 3628 and a rising time ( tr) and a decay time ( td) of 3.52 and 0.33 s upon UV exposure, along with excellent NO2-sensing characteristics with a stable gas on-off ratio of 288.5 and a tr and td of 38 and 62 s upon NO2 exposure. Furthermore, the sensors grown on the Ag NP template exhibited good mechanical flexibility and stable sensing properties without significant degradation even after the bending test up to 10 000 cycles at the bending radius of 5 mm.
ABSTRACT
Poly(9,9-dioctylfluorene) (PFO) has attracted significant interests owing to its versatility in electronic devices. However, changes in its optical properties caused by its various phases and the formation of oxidation defects limit the application of PFO in light-emitting diodes (LEDs). We investigated the effects of the addition of Triton X-100 (hereinafter shortened as TX) in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to induce interlayer diffusion between PEDOT:PSS and PFO to enhance the stability of the PFO phase and suppress its oxidation. Photoluminescence (PL) measurement on PFO/TX-mixed PEDOT:PSS layers revealed that, upon increasing the concentration of TX in the PEDOT:PSS layer, the ß phase of PFO could be suppressed in favor of the glassy phase and the wide PL emission centered at 535 nm caused by ketone defects formed by oxidation was decreased considerably. LEDs were then fabricated using PFO as an emission layer, TX-mixed PEDOT:PSS as hole-transport layer, and zinc oxide (ZnO) nanorods as electron-transport layer. As the TX concentration reached 3 wt %, the devices exhibited dramatic increases in current densities, which were attributed to the enhanced hole injection due to TX addition, along with a shift in the dominant emission wavelength from a green electroluminescence (EL) emission centered at 518 nm to a blue EL emission centered at 448 nm. The addition of TX in PEDOT:PSS induced a better hole injection in the PFO layer, and through interlayer diffusion, stabilized the glassy phase of PFO and limited the formation of oxidation defects.
ABSTRACT
The morphology of perovskite films has a significant impact on luminous characteristics of perovskite light-emitting diodes (PeLEDs). To obtain a highly uniform methylammonium lead tribromide (MAPbBr3) film, a gas-assisted crystallization method is introduced with a mixed solution of MAPbBr3 precursor and polymer matrix. The ultrafast evaporation of the solvent causes a high degree of supersaturation which expedites the generation of a large number of nuclei to form a MAPbBr3-polymer composite film with full surface coverage and nano-sized grains. The addition of the polymer matrix significantly affects the optical properties and morphology of MAPbBr3 films. The PeLED made of the MAPbBr3-polymer composite film exhibits an outstanding device performance of a maximum luminance of 6800 cd·m-2 and a maximum current efficiency of 1.12 cd·A-1. Furthermore, 1 cm2 area pixel of PeLED displays full coverage of a strong green electroluminescence, implying that the high-quality perovskite film can be useful for large-area applications in perovskite-based optoelectronic devices.
ABSTRACT
Micropatternable double-faced (DF) zinc oxide (ZnO) nanoflowers (NFs) for flexible gas sensors have been successfully fabricated on a polyimide (PI) substrate with single-walled carbon nanotubes (SWCNTs) as electrode. The fabricated sensor comprises ZnO nanoshells laid out on a PI substrate at regular intervals, on which ZnO nanorods (NRs) were grown in- and outside the shells to maximize the surface area and form a connected network. This three-dimensional network structure possesses multiple gas diffusion channels and the micropatterned island structure allows the stability of the flexible devices to be enhanced by dispersing the strain into the empty spaces of the substrate. Moreover, the micropatterning technique on a flexible substrate enables highly integrated nanodevices to be fabricated. The SWCNTs were chosen as the electrode for their flexibility and the Schottky barrier they form with ZnO, improving the sensing performance. The devices exhibited high selectivity toward NO2 as well as outstanding sensing characteristics with a stable response of 218.1, fast rising and decay times of 25.0 and 14.1 s, respectively, and percent recovery greater than 98% upon NO2 exposure. The superior sensing properties arose from a combination of high surface area, numerous active junction points, donor point defects in the ZnO NRs, and the use of the SWCNT electrode. Furthermore, the DF-ZnO NF gas sensor showed sustainable mechanical stability. Despite the physical degradation observed, the devices still demonstrated outstanding sensing characteristics after 10 000 bending cycles at a curvature radius of 5 mm.
