High-Performance Flexible Ultraviolet Photodetectors with Ni/Cu-Codoped ZnO Nanorods Grown on PET Substrates

Abstract

As a developing technology for flexible electronic device fabrication, ultra-violet (UV) photodetectors (PDs) based on a ZnO nanostructure are an effective approach for large-area integration of sensors on nonconventional substrates, such as plastic or paper. However, photoconductive ZnO nanorods grown on flexible substrates have slow responses or recovery as well as low spectral responsivity R because of the native defects and inferior crystallinity of hydrothermally grown ZnO nanorods at low temperatures. In this study, ZnO nanorod crystallites are doped with Cu or Ni/Cu when grown on polyethylene terephthalate (PET) substrates in an attempt to improve the performance of flexible PDs. The doping with Ni/Cu or Cu not only improves the crystalline quality but also significantly suppresses the density of deep-level emission defects in as-grown ZnO nanorods, as demonstrated by X-ray diffraction and photoluminescence. Furthermore, the X-ray photoelectron spectroscopy analysis shows that doping with the transition metals significantly increases the oxygen bonding with metal ions with enhanced O/Zn stoichiometry in as-grown nanorods. The fabricated flexible PD devices based on an interdigitated electrode structure demonstrates a very high R of ~123 A/W, a high on-off current ratio of ~130, and a significant improvement in transient response speed exhibiting rise and fall time of ~8 and ~3 s, respectively, by using the ZnO nanorods codoped by Ni/Cu.

Ultraviolet Photodetection Based on High-Performance Co-Plus-Ni Doped ZnO Nanorods Grown by Hydrothermal Method on Transparent Plastic Substrate

“…This can be related to the increased diameter of NR crystals after doping in pristine ZnO NRs [ 30 ]. The (002) reflections from TM-doped NRs were shifted slightly toward higher angles than that of the undoped ones, and this result was in good agreement with our recent Cu doping experimental observation [ 31 ], which validates the potential substitution of Zn 2+ by either Ni 2+ or Co 2+ in the host crystal of ZnO. However, a small amount of shift in (002) reflection can be associated with the insignificant mismatch in atomic radii of Ni (0.69 Å) or Co (0.72 Å) with that of Zn (0.74 Å) [ 32 , 33 ].…”

“…As shown in PL spectra of Figure 4 a, we could observe two clear zones of UV emission (350–400 nm) and broad-band visible emission (400–760 nm) from each sample. The UV emission of near band emission (NBE) arises from excitonic band-to-band recombination in ZnO [ 15 , 31 ]. As shown in PL spectra, significantly enhanced UV emissions were shown from the TM-doped nanocrystals.…”

“…In this case, the lateral expansion of NR crystals in diameter and the increase in surface density after TM-doping, as shown in Figure 3 , can be the prime factors contributing to the enhancement of absorption. The increase of UV absorption can be also associated with larger crystal volume after the dopant incorporation causing the greater photon absorption due to Mie light scattering [ 31 ] that is optimized when the scattering materials have a diameter comparable to or greater than the incident light wavelength. Moreover, the doped NR crystals exhibited the minor absorbance humps in a range of 550 and 690 nm indicating the exchange interaction of ZnO free electrons with the localized electrons in 3d energy levels of dopants.…”

Fabrication and Potential Applications of Highly Durable Superhydrophobic Polyethylene Terephthalate Fabrics Produced by In-Situ Zinc Oxide (ZnO) Nanowires Deposition and Polydimethylsiloxane (PDMS) Packaging

“…Numerous methods were used to ameliorate the surface energy of polyethylene terephthalate (PET) fabrics, such as oxygen plasma treatment, chemical passivation etc. Ajmal et al [ 28 ] treated the PET surface by using oxygen plasma to convert the surface state, which can improve the interface bonding strength. Zhou et al [ 29 ] used chemical passivation to increase the surface roughness for promoting the attachment of ZnO nanolayers.…”

Ultraviolet Photodetecting and Plasmon-to-Electric Conversion of Controlled Inkjet-Printing Thin-Film Transistors

“…Many studies have made several attempts to develop a metal-oxide semiconducting-based photodetecting. Metal-oxide semiconducting materials-based TFTs are considered to be the most appropriate photodetecting devices because of their characteristics of being transparent, low-cost and fast photoresponse in the ultraviolet wavelength region [23][24][25][26][27][28]. However, the metal-oxide semiconducting materials based photodetector can convert only ultraviolet (UV) wavelength light to electrical signal.…”