Light‐Emitting Diodes with Cu‐Doped Colloidal Quantum Wells: From Ultrapure Green, Tunable Dual‐Emission to White Light

Abstract

Copper‐doped colloidal quantum wells (Cu‐CQWs) are considered a new class of optoelectronic materials. To date, the electroluminescence (EL) property of Cu‐CQWs has not been revealed. Additionally, it is desirable to achieve ultrapure green, tunable dual‐emission and white light to satisfy the various requirement of display and lighting applications. Herein, light‐emitting diodes (LEDs) based on colloidal Cu‐CQWs are demonstrated. For the 0% Cu‐doped concentration, the LED exhibits Commission Internationale de L'Eclairage 1931 coordinates of (0.103, 0.797) with a narrow EL full‐wavelength at half‐maximum of 12 nm. For the 0.5% Cu‐doped concentration, a dual‐emission LED is realized. Remarkably, the dual emission can be tuned by manipulating the device engineering. Furthermore, at a high doping concentration of 2.4%, a white LED based on CQWs is developed. With the management of doping concentrations, the color tuning (green, dual‐emission to white) is shown. The findings not only show that LEDs with CQWs can exhibit polychromatic emission but also unlock a new direction to develop LEDs by exploiting 2D impurity‐doped CQWs that can be further extended to the application of other impurities (e.g., Mn, Ag).

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

“…CQW‐LEDs are highly promising for display and lighting applications, owing to their high color purity with ultranarrow full‐width at half‐maximum (FWHM), easy solution‐processed fabrication procedures, and good compatibility with flexible electronics . In the past few years, some efforts have been made to develop CQW‐LEDs .…”

“…Most importantly, the CQWs should have an excellent photoluminescence quantum yield (PLQY), which is essential to warrant the high efficiency . However, the PLQY of CQWs used in LEDs is not sufficiently high . In the case of core CQWs, the surface nonradiative recombination sites will easily deteriorate the efficiency, leading to the inefficient core‐only‐based CQW‐LEDs .…”

“…However, the PLQY of CQWs used in LEDs is not sufficiently high . In the case of core CQWs, the surface nonradiative recombination sites will easily deteriorate the efficiency, leading to the inefficient core‐only‐based CQW‐LEDs . To reduce surface traps, the growth of a semiconductor layer around the core CQWs is useful, which can increase the PLQY and decrease emission blinking at a single particle level .…”

“…In addition, the effect of the physical shape of CQWs on the device performance remains unknown, which might affect the film morphology of spin‐coated CQWs in LEDs. Furthermore, the surface of previously reported CQW films is not smooth enough, which may lead to detrimental current leakage and other losses . Moreover, the employment of hybrid organic‐inorganic device architectures is considered to be the most effective scheme to ensure high‐efficiency CQD‐LEDs .…”

“…Consequently, CQW‐LEDs using CdSe/Cd 0.25 Zn 0.75 S core/c‐ALD shell show poor performance. However, it is deserved to note that no CQW film used in LEDs has been previously demonstrated to exhibit an RMS roughness of ≤3 nm, indicating that the HIS technique (e.g., an RMS roughness of 2.23 nm) provides a new pathway to effectively smoothen the film surface.…”