ABSTRACT
Layered metal-halide perovskites, or two-dimensional perovskites, can be synthesized in solution, and their optical and electronic properties can be tuned by changing their composition. We report a molecular templating method that restricted crystal growth along all crystallographic directions except for [110] and promoted one-dimensional growth. Our approach is widely applicable to synthesize a range of high-quality layered perovskite nanowires with large aspect ratios and tunable organic-inorganic chemical compositions. These nanowires form exceptionally well-defined and flexible cavities that exhibited a wide range of unusual optical properties beyond those of conventional perovskite nanowires. We observed anisotropic emission polarization, low-loss waveguiding (below 3 decibels per millimeter), and efficient low-threshold light amplification (below 20 microjoules per square centimeter).
ABSTRACT
Halide perovskites have potential for use in next-generation low-cost, high-efficiency, and highly color-pure light-emitting diodes (LED) that can be used in various applications, such as flat and flexible displays and solid-state lighting. However, they still lag behind other mature technologies, such as organic LEDs and inorganic LEDs, in terms of performance, particularly brightness. This lag is partly due to the insulating nature of the long-chain organic ligands used to control the perovskite-film morphology. Herein, a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (IL) is incorporated as a potential additive with CsPbBr3 perovskite precursors, which results in a super-bright green perovskite light emitting diode (PeLED) achieving a peak luminance of 3.28 × 105 cd m-2 only at a bias voltage of 6 V, with a peak external quantum efficiency of 13.75%. This achievement is the outcome of multirole support from IL that simultaneously enables superior control over the perovskite-film morphology, passivates defects, modifies the band energy levels, and prevents ion migration. Hence, this work demonstrates IL as a novel alternative additive with the potential to outperform conventional long-chain ligands in high-performance PeLED device fabrication.
ABSTRACT
As the lighting technology evolves, the need for violet light-emitting diodes (LEDs) is growing for high color rendering index lighting. The present technology for violet LEDs is based on the high-cost GaN materials and metal-organic chemical vapor deposition process; therefore, there have recently been intensive studies on developing low-cost alternative materials and processes. In this study, for the first time, we demonstrated violet LEDs based on low-cost materials and processes using a p-CuI thin film/n-MgZnO quantum dot (QD) heterojunction. The p-CuI thin film layer was prepared by an iodination process of Cu films, and the n-MgZnO layer was deposited by spin-coating presynthesized n-MgZnO QDs. To maximize the performance of the violet LED, an optimizing process was performed for each layer of p- and n-type materials. The optimized LED with 1 × 1 mm2-area pixel fabricated using the p-CuI thin film at the iodination temperature of 15 °C and the n-MgZnO QDs at the Mg alloying concentration of 2.7 at. % exhibited the strongest violet emissions at 6 V.
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
In this study, plasmonic silver (Ag) nanoparticle-(NP) anchored ZnO nanorods (NRs) and nanotube-(NT) based UV photodetectors are demonstrated. Here, Ag NPs are synthesized and anchored by using a room-temperature photochemical method by exposing the precursor solution in UV radiation. In order to achieve a stronger surface plasmon resonance (SPR) and minimum agglomeration, the photochemical method is optimized with a precursor concentration of 5 mmol, a UV intensity of 0.4 mW · cm-2, and an exposure time of 30 min. An asymmetry around 380 nm in the absorption spectra of the NP solution indicates the presence of plasmonic resonance in that region. Upon anchoring the Ag NPs, ZnO NRs show enhanced band edge emission (380-400 nm) and the emission is further significantly increased in Ag NP-anchored ZnO NTs. The on/off ratio and photoresponse properties of the UV photodetectors are enhanced significantly after anchoring Ag NPs on the ZnO nanostructures. It is believed that the near-field coupling of SPR causes an optical enhancement of ZnO, whereas the bridging effect and hot-electron transfer to the conduction band of ZnO by plasmonic Ag NPs, anchored in close proximity, gives rise to a faster response of the photodetectors.
ABSTRACT
This study explores low-temperature solution-process-based seed-layer-free ZnO p-n homojunction light-emitting diode (LED). In order to obtain p-type ZnO nanodisks (NDs), antimony (Sb) was doped into ZnO by using a facile chemical route at 120 °C. The X-ray photoelectron spectra indicated the presence of (SbZn-2VZn) acceptor complex in the Sb-doped ZnO NDs. Using these NDs as freestanding templates, undoped n-type ZnO nanorods (NRs) were epitaxially grown at 95 °C to form ZnO p-n homojunction. The homojunction with a turn-on voltage of 2.5 V was found to be significantly stable up to 100 s under a constant voltage stress of 5 V. A strong orange-red emission was observed by the naked eye under a forward bias of 5 V. The electroluminescence spectra revealed three major peaks at 400, 612, and 742 nm which were attributed to the transitions from Zni to VBM, from Zni to Oi, and from VO to VBM, respectively. The presence of these deep-level defects was confirmed by the photoluminescence of ZnO NRs. This study paves the way for future applications of ZnO homojunction LEDs using low-temperature and low-cost solution processes with the controlled use of native defects.
ABSTRACT
We report low-temperature solution-processed p-CuO nanorods (NRs)/n-ZnO NRs heterojunction light emitting diode (LED), exploiting the native point defects of ZnO NRs. ZnO NRs were synthesized at 90 °C by using hydrothermal method while CuO NRs were synthesized at 100 °C by using microwave reaction system. The electrical properties of newly synthesized CuO NRs revealed a promising p-type nature with a hole concentration of 9.64 × 10(18) cm(-3). The current-voltage characteristic of the heterojunction showed a significantly high rectification ratio of 10(5) at 4 V with a stable current flow. A broad orange-red emission was obtained from the forward biased LED with a major peak at 610 nm which was attributed to the electron transition from interstitial zinc to interstitial oxygen point defects in ZnO. A minor shoulder peak was also observed at 710 nm, corresponding to red emission which was ascribed to the transition from conduction band of ZnO to oxygen vacancies in ZnO lattice. This study demonstrates a significant progress toward oxide materials based, defect-induced light emitting device with low-cost, low-temperature methods.