Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes

be grown epitaxially on specific substrates, silicon not being one of them.Metal halide perovskite light-emitting diodes (PeLEDs) hold the potential for a new generation of display and lighting technology, [1][2][3][4][5][6][7] featuring high color quality, energy efficiency, and low manufacturing cost. Furthermore, perovskites can be deposited from solutions/inks, which means that they can be deposited on virtually any substrate including silicon. Perovskite LEDs have been shown to be promising for optical communications. [8] However, the operation speed of PeLEDs is still relatively slow, with electroluminescence (EL) rise times of several hundred nanoseconds or longer. [9][10][11][12] The slow operation speed and response time of PeLEDs limit their potential for a wider scope of applications, such as interchip and intrachip optical communications, currently realized with more expensive technologies using III-V semiconductors.Reducing the EL rise time of PeLEDs will not only increase their potential utility for applications in optical communications, but also contribute to the development of an electrically driven perovskite laser diode, which would be transformative in the optoelectronics realm as a low-cost laser source compatible with silicon microelectronics. Despite significant progress toward this goal, [13][14][15][16] electrically driven lasing in perovskites has not yet been achieved. One challenge is that the current density reported to date does not exceed the estimated threshold required for lasing. Reducing the EL rise time would enable shorter pulse operation, making it possible for PeLEDs to operate at higher current densities due to reduced Joule heating. [10,17] Furthermore, high-speed pulsed operation of PeLEDs will allow us to probe electrically stimulated chargecarrier dynamics and reveal mechanisms that prevent PeLEDs from operating efficiently or lasing under electrical excitation. This understanding is particularly important as optically pumped lasing death has been observed for perovskite thin films within 25 ns, [18] and optical and electrical excitations are considerably distinct.Both extrinsic factors (e.g., parasitic capacitance and resistance) and intrinsic factors (e.g., long recombination lifetime of charge carriers in the light-generating process) can limit the speed of PeLEDs. However, the speed of PeLEDs reported so far appears to have been dominantly constrained by extrinsic factors, [8][9][10][11][12] excluding the possibility to probe more intrinsic While metal-halide perovskite light-emitting diodes (PeLEDs) hold the potential for a new generation of display and lighting technology, their slow operation speed and response time limit their application scope. Here, high-speed PeLEDs driven by nanosecond electrical pulses with a rise time of 1.2 ns are reported with a maximum radiance of approximately 480 kW sr −1 m −2 at 8.3 kA cm −2 , and an external quantum efficiency (EQE) of 1% at approximately 10 kA cm −2 , through improved device configuration designs and material consi...

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confidence: 99%

Nanosecond‐Pulsed Perovskite Light‐Emitting Diodes at High Current Density

et al. 2021

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“…Optical cavity, an ideal platform for modulating the emitted photons, provides us a powerful tool for constructing electroluminescent panels with higher spectral purity. A thin‐film LED stack forms a microcavity between a metal electrode and an ITO anode (Figure 2b), accompanying with a Lambertian‐like air mode emission profile due to the weak cavity effects, [ 46 ] which has negligible effect on the spectral linewidth. To this end, a microcavity concluding a bottom metal mirror and a top DBR was designed (Figure 2c).…”

Section: Resultsmentioning

confidence: 99%

“…[ 44,45 ] Since the resonance‐enhanced emission is directed along the optical axis of the cavity, a small beam divergence was demonstrated in such cavity‐based devices, showing great potential for near‐eye displays such as virtual reality and augmented reality. [ 46,47 ] With each microsized PeLED serves as a pixel, electrically driven displays with outstanding color expression were realized. Varied contents were dynamically displayed under the assistance of a microelectrode array, which manifests the feasibility for display applications.…”

Section: Introductionmentioning

confidence: 99%

Ultrahigh Color Rendering in RGB Perovskite Micro‐Light‐Emitting Diode Arrays with Resonance‐Enhanced Photon Recycling for Next Generation Displays

Liang

Wang

et al. 2021

Advanced Optical Materials

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Light sources with high color purity are promising for revolutionizing traditional displays because of their wide achievable color gamut, high contrast ratio, and good color saturation. The demand for next‐generation displays has driven the development of the optoelectronic materials with narrow linewidth. Until now, most optoelectronic materials usually give emission with full width at half maximum exceeding 30 nm. The lack of a general approach to further improving the color purity has limited their applications for next‐generation displays. Here, a universal resonance‐enhanced photon recycling strategy is developed to realize current‐driven displays with unprecedented high color rendering based on the perovskite light‐emitting diode (LED) arrays in distributed Bragg reflector (DBR) cavity. Benefiting from the outstanding optoelectronic properties and solution processability, perovskites are processed into micro‐LED arrays through a screen‐printing technology. The light output from individual micro‐LED is strongly modulated by resonance‐enhanced photon recycling derived from the cavity structure, leading to significant spectral narrowing and directional emission. On this basis, unprecedented high‐color‐purity is achieved in a prototype of current‐driven display panels. The outstanding performance of red, green, and blue (RGB) micro‐LED arrays with resonance‐enhanced photon recycling provides a deep insight into the design concepts and device structures for next‐generation display technology.

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“…Hereby, an effect called ray ping pong is identified to be responsible for the improved directional emission of white light. Related effects like photon recycling 40 were studied in previous work for solar GaAs cells [41][42][43] , perovskite LEDs 44 or thin films themselves 45 . In our work, depending on their wavelength and incident angle, the rays are considered to be partially trapped in the LED package by an MLTF, enforcing interactions between rays and LED package materials like scattering, (re-)absorbtion, (re-)emission or non-radiative effects.…”

Section: State Of the Artmentioning

confidence: 99%

Playing Ping Pong With Light: Directional Emission of White Light

Wankerl

Wiesmann

Kreiner

et al. 2021

Preprint

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Over the last decades, light-emitting diodes (LED) have replaced common light bulbs in almost every application, from flashlights in smartphones to automotive headlights. Illuminating nightly streets requires LEDs to emit a light spectrum that is perceived as pure white by the human eye. The power associated with such a white light spectrum is not only distributed over the contributing wavelengths but also over the angles of vision. For many applications, the usable light rays are required to exit the LED in forward direction, namely under small angles to the perpendicular. In this work, we demonstrate that a specifically designed multi-layer thin film on top of a white LED increases the power of pure white light emitted in forward direction. Therefore, the deduced multi-objective optimization problem is reformulated via a real-valued physics-guided objective function that represents the hierarchical structure of our engineering problem. Variants of Bayesian optimization are employed to maximize this non-deterministic objective function based on ray tracing simulations. Eventually, the investigation of optical properties of suitable multi-layer thin films allowed to identify the mechanism behind the increased directionality of white light: angle and wavelength selective filtering causes the multi-layer thin film to play ping pong with rays of light.

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Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes

Cited by 41 publications

References 51 publications

Nanosecond‐Pulsed Perovskite Light‐Emitting Diodes at High Current Density

Nanosecond‐Pulsed Perovskite Light‐Emitting Diodes at High Current Density

Ultrahigh Color Rendering in RGB Perovskite Micro‐Light‐Emitting Diode Arrays with Resonance‐Enhanced Photon Recycling for Next Generation Displays

Playing Ping Pong With Light: Directional Emission of White Light

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