Record High External Quantum Efficiency of 19.2% Achieved in Light‐Emitting Diodes of Colloidal Quantum Wells Enabled by Hot‐Injection Shell Growth

Abstract

Colloidal quantum wells (CQWs) are regarded as a highly promising class of optoelectronic materials, thanks to their unique excitonic characteristics of high extinction coefficients and ultranarrow emission bandwidths. Although the exploration of CQWs in light‐emitting diodes (LEDs) is impressive, the performance of CQW‐LEDs lags far behind other types of soft‐material LEDs (e.g., organic LEDs, colloidal‐quantum‐dot LEDs, and perovskite LEDs). Herein, high‐efficiency CQW‐LEDs reaching close to the theoretical limit are reported. A key factor for this high performance is the exploitation of hot‐injection shell (HIS) growth of CQWs, which enables a near‐unity photoluminescence quantum yield (PLQY), reduces nonradiative channels, ensures smooth films, and enhances the stability. Remarkably, the PLQY remains 95% in solution and 87% in film despite rigorous cleaning. Through systematically understanding their shape‐, composition‐, and device‐engineering, the CQW‐LEDs using CdSe/Cd0.25Zn0.75S core/HIS CQWs exhibit a maximum external quantum efficiency of 19.2%. Additionally, a high luminance of 23 490 cd m−2, extremely saturated red color with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.715, 0.283), and stable emission are obtained. The findings indicate that HIS‐grown CQWs enable high‐performance solution‐processed LEDs, which may pave the path for future CQW‐based display and lighting technologies.

Halide Perovskite Lateral Heterostructures for Energy Routing Based Photonic Applications

“…High‐quality semiconductor heterostructures lay the foundation of modern semiconductor optoelectronics, especially for the light‐emitting devices and lasers, by virtue of the controllable optical and electronic properties via on‐demand electronic structure engineering. [ 1–5 ] Developing new kinds of semiconductor heterostructures with novel optoelectronic properties is always pursued with regard to meet the rising demand of device miniaturization and functionization. For instance, in the past decades, it has been witnessed that the advance of heterostructure technology results in the much improved device performance and new device functionalities.…”

Optical Gain in Ultrathin Self‐Assembled Bi‐Layers of Colloidal Quantum Wells Enabled by the Mode Confinement in their High‐Index Dielectric Waveguides

“…The synthesis method and recipe of the core/alloyed HIS CQWs are nearly similar to the previous reports. [ 9,10 ] 4 ML thick CdSe core CQWs solution in hexane with an optical density of 2 at 350 nm wavelength (using 1 cm long optical path) was used. 55.04 mg Zn‐acetate, 5 mL of 1‐octadecene (ODE), 23.06 mg of Cd‐acetate, 0.70 mL oleic acid, and 1 mL of CdSe core were mixed in a three‐necked quartz flask (50 mL).…”

“…[8] Among such solution-processable materials, colloidal quantum wells (CQWs), the atomically flat member of semiconductor nanocrystal family, have been the focus of increasing attention thanks to their excellent electronic and optical properties for optoelectronic applications. [9][10][11][12] CQWs exhibit narrow spontaneous emission spectra, suppressed inhomogeneous broadening, giant oscillator strength, and high density of energy states at the band edge, which are highly desired for optical gain and lasing. [13][14][15] Optical gain and lasing using a few hundred nanometers to micrometer thick CQW active regions have thus far been reported.…”

Advances in Perovskite Light-Emitting Diodes Possessing Improved Lifetime

“…For example, the typical HTL 4,4-N,N-dicarbazolebiphenyl (CBP) is not only prone to crystallization due to a low glass transition temperature (62 • C) but also electrochemically decomposed to act as nonradiative recombination centers and/or luminance quenchers during device operation, decreasing the stability [82]. Recently, Liu et al achieved 4.5-fold longer lifetime in colloidal LEDs by replacing CBP with relatively stable HTL N,N -di-(1-naphthyl)-N,N -diphenyl-(1,1 -biphenyl)-4,4 -diamine (NPB)/4,4 ,4 -tris(carbazol-9-yl)-triphenylamine (TCTA) [83]. (ii) The stability of PeLEDs is strongly associated with charge balance [84][85][86].…”

“…The maximum internal quantum efficiency (IQE) of PeLEDs is supposed to be 100%, whereas the EQE (η ext ) is decided by the outcoupling factor (η out ), the fraction of excitons that can potentially radiatively decay (r), PLQY (q), and charge balance (γ), which is written as [83]:…”