Screen-Overprinted Perovskite RGB Microdisk Arrays Based on Wet-Solute-Chemical Dynamics for Full-Color Laser Displays

Colloidal-quantum-dot nanolaser oscillating at a bound-state-in-the-continuum with planar surface topography for a high Q-factor

Solution-based optical gain materials offer a cost-effective path to coherent light sources. Further, bound states in the continuum (BICs) have garnered great interest owing to their diverging quality (Q) factors. Therefore, a hybrid of these - a solution-based material for optical gain and a BIC structure for the lasing mode - should constitute an ideal form factor for low-cost and low-threshold nanolasers. However, the nonuniform surface topography induced during the thin-film formation of a solution-based material, especially on top of a prepatterned substrate, can easily disrupt the structural symmetry required for a high-Q BIC, resulting in a degradation of Q. Thus, in this study, a simple surface-flattening technique utilizing a soft and flexible squeegee was applied, which realized the planar surface topography crucial for preserving the high Q promised by the BIC and achieving low-threshold lasing. We fabricated BIC nanolasers by incorporating colloidal quantum dots (CQDs) for optical gain into a two-dimensional photonic crystal backbone layer composed of Si3N4. By leveraging the unique properties of the BIC mode with a well-ordered surface, our CQD-based BIC laser exhibited a lasing threshold as low as 10.5 kW/cm2, which is significantly lower than those reported in previous studies.

Optically Pumped and Electrically Switchable Microlaser Array Based on Elliptic Deformation and Q-Attenuation of Organic Droplet Oscillators

Conventional laser panel displays are developed through the mass integration of electrically pumped lasers or through the incorporation of a beam steering system with an array of optically pumped lasers. Here a novel configuration of a laser panel display consisting of a non-steered pumping beam and an array of electrically Q-switchable lasers is reported. The laser oscillator consists of a robust, self-standing, and deformable minute droplet that emits laser through Whispering-Gallery Mode resonance when optically pumped. The laser oscillation is electrically switchable during optical pumping by applying a vertical electric field to the droplet. Electromagnetic and fluid dynamics simulations reveal the deformation of the droplet into a prolate spheroid under the electric field and associated attenuation of quality factor (Q-factor), leading to the halt of the laser oscillation. A 2 × 3 array of droplets is fabricated by inkjet printing as a prototype of a laser panel display, and it successfully achieves the pixel-selective switching of the oscillation.

All-inorganic lead halide perovskite nanocrystals applied in advanced display devices

Advanced display devices are in greater demand due to their large color gamut, high color purity, ultrahigh visual resolution, and small size pixels. All-inorganic lead halide perovskite (AILHP) nanocrystals (NCs) possess inherent advantages such as narrow emission width, saturated color, and flexible integration, and have been developed as functional films, light sources, backlight components, and display panels. However, some drawbacks still restrict the practical application of advanced display devices based on AILHP NCs, including working stability, large-scale synthesis, and cost. In this review, we focus on AILHP NCs, review the recent progress in materials synthesis, stability improvement, patterning techniques, and device application. We also highlight the important role of materials systems in creating advanced display devices, followed by the challenges and opportunities in industrial processes. This review provides beneficial inspiration for the future development of AILHP NCs in colorful and white backlight, as well as high resolution full-color displays.

Flexible Microspectrometers Based on Printed Perovskite Pixels with Graded Bandgaps

Miniaturized spectrometers have attracted much attention due to their capability to detect spectral information within a small size. However, such technology still faces challenges including large-scale preparation and performance repeatability. In this work, we overcome these challenges by demonstrating a microspectrometer constructed with a series of pixelized graded-bandgap perovskite photodetectors fabricated with inkjet printing. High-quality perovskite films with minimal pinholes and large grains are deposited by optimizing printing conditions including substrate temperature and surface modification. The resulting perovskite photodetectors show decent photosensing performance, and the different photodetectors based on perovskite films with different bandgaps exhibit various spectral responsivities with different cutoff wavelength edges. Microspectrometers are then constructed with the array of the pixelized graded-bandgap perovskite photodetectors, and incident spectra are algorithmically reconstructed by combining their output currents. The reconstruction performance of the miniaturized spectrometer is evaluated by comparing the results to the spectral curve measured with a commercial bulky spectrometer, indicating a reliable spectral reconstruction with a resolution of around 10 nm. More significantly, the miniaturized spectrometers are successfully fabricated on polymer substrates, and they demonstrate excellent mechanical flexibility. Therefore, this work provides a flexible miniaturized spectrometer with large-scale fabricability, which is promising for emerging applications including wearable devices, hyperspectral imaging, and internet of things.

Perovskite-Gallium Nitride Tandem Light-Emitting Diodes with Improved Luminance and Color Tunability

Tandem structures with different subpixels are promising for perovskite-based multicolor electroluminescence (EL) devices in ultra-high-resolution full-color displays; however, realizing excellent luminance- and color-independent tunability considering the low brightness and stability of blue perovskite light-emitting diodes (PeLEDs) remains a challenge. Herein, a bright and stable blue gallium nitride (GaN) LED is utilized for vertical integration with a green MAPbBr3 PeLED, successfully achieving a Pe-GaN tandem LED with independently tunable luminance and color. The electronic and photonic co-excitation (EPCE) effect is found to suppress the radiative recombination and current injection of PeLEDs, leading to degraded luminance and current efficiency under direct current modulation. Accordingly, the pulse-width modulation is introduced to the tandem device with a negligible EPCE effect, and the average hybrid current efficiency is significantly improved by 139.5%, finally achieving a record tunable luminance (average tuning range of 16631 cd m-2 at an arbitrary color from blue to green) for perovskite-based multi-color LEDs. The reported excellent independent tunability can be the starting point for perovskite-based multicolor EL devices, enabling the combination with matured semiconductor technologies to facilitate their commercialization in advanced display applications with ultra-high resolution.