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Efficient Two-Dimensional Tin Halide Perovskite Light-Emitting Diodes via a Spacer Cation Substitution Strategy
摘要： Lead halide perovskites have attracted tremendous attention due to their impressive optoelectronic properties. However, the toxicity of lead remains to be a bottleneck for further commercial development. Two-dimensional Ruddlesden-Popper tin-based perovskites are lead-free and more stable compared to their 3D counterparts, which have great potential in the optoelectronic device field. Herein, we demonstrated high-quality 2D phenylethyl ammonium tin-iodide perovskite (PEA2SnI4) thin films by dropping toluene as anti-solvent. Furthermore, the PeLED performance is greatly improved by replacing PEAI spacer cation with 2-thiopheneethyllamine iodide (TEAI). As a result, the TEA-based PeLED device is achieved with a low turn-on voltage of 2.3V, a maximum luminance of 322 cd m-2 and maximum external quantum efficiency of 0.62%, which is the highest efficiency and brightness for pure red (emission peak=638 nm) tin-based PeLEDs so far.
关键词： pure red light-emitting diodes,two-dimensional tin-based perovskite,spacer cation substitution
更新于2025-09-16 10:30:52
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Wireless phototherapeutic contact lenses and glasses with red light-emitting diodes
摘要： Light-mediated therapeutics have attracted considerable attention as a method for the treatment of ophthalmologic diseases, such as age-related macular degeneration, because of their non-invasiveness and the effectiveness to ameliorate the oxidative stress of retinal cells. However, the current phototherapeutic devices are opaque, bulky, and tethered forms, so they are not feasible for use in continuous treatment during the patient’s daily life. Herein, we report wireless, wearable phototherapeutic devices with red light-emitting diodes for continuous treatments. Red light-emitting diodes were formed to be conformal to three-dimensional surfaces of glasses and contact lenses. Furthermore, fabricated light-emitting diodes had either transparency or a miniaturized size so that the user’s view is not obstructed. Also, these devices were operated wirelessly with control of the light intensity. In addition, in-vitro and in-vivo tests using human retinal epithelial cells and a live rabbit demonstrated the effectiveness and reliable operation as phototherapeutic devices.
关键词： wearable healthcare,phototherapies,red light-emitting diodes,transparent electronics
更新于2025-09-12 10:27:22
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16.3: <i>Invited Paper:</i> New development in Red Light‐emitting Diodes (LEDs) using Eu‐doped GaN for Monolithic Micro‐LED Displays
摘要： There has been a strong demand to develop red light-emitting nitride semiconductors for the monolithic integration of the three primary colors (RGB) and the development of a high-resolution display. Such a display is a key device for 'a smart society', in which cyberspace (information processing) and physical space (things) interactively fuse. The ongoing search for an efficient red LED based on GaN is pivotal to those efforts. In blue and green LEDs, InxGa1-xN /GaN multi-quantum wells are used as an active layer. Emission wavelength is determined by In composition in the InGaN. A simple way to realize the red LED is to increase In composition to 0.5. However, lattice mismatch between InGaN and GaN becomes large in InGaN with high In composition, which leads to severe degradation of crystalline quality of InGaN quantum wells. Furthermore, lattice mismatch also induces huge piezoelectric field, resulting in poor radiative recombination due to quantum-confined Stark effects. We have worked on the development of semiconductors intra-center photonics. This novel photonics uses the intra-4f shell transitions of rare-earth ions doped in semiconductors. In 2009, we invented a narrow-band red LED using Eu-doped GaN (GaN:Eu). A main emission line with a half width of less than 1 nm is observed at 621 nm, which can be assigned to the 5D0–7F2 transition of Eu3+ ions. The wavelength is extremely stable against the ambient temperature. Due to optimization of the device processing, the output power of the LED has been increasing steadily to over 1 mW. Utilizing this red LED, small nitride-based monolithic high-resolution optical devices that comprise RGB GaN-based LEDs can be realized for micro-LED displays and/or lighting technology. One of limiting factors for more enhanced light output power is a relatively long radiative lifetime of the Eu emission in GaN:Eu (～300 μs). According to the Fermi’s golden rule, modifying the spontaneous emission rate of Eu ions can be achieved by increasing the photonic density of states at the frequency of spontaneous emission, as already demonstrated with a planar Fabry-Perot cavity. We have boosted the output power by actively manipulating radiative recombination probability at the atomic level of the Eu ions, which can be achieved through control of their photon fields in micro- and nano-cavities. In a GaN:Eu layer embedded in a microcavity consisting of an AlGaN/GaN distributed Bragg reflector (DBR) and a Ag reflecting mirror, a 21-fold increase of the Eu emission intensity was obtained under optical pumping at room temperature. Furthermore, in a preliminary LED with a microcavity consisting of ZrO2/SiO2 and AlInN/GaN DBRs, the output power was enhanced by 10 times. In the talk, current status of the LED and strategies for more improved output power will be presented.
关键词： Monolithic Micro-LED Displays,Eu-doped GaN,Intra-center photonics,Red Light-emitting Diodes,Nitride semiconductors
更新于2025-09-11 14:15:04