Ultrapure Green Light-Emitting Diodes Using Two-Dimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates

Abstract

Pure green light-emitting diodes (LEDs) are essential for realizing an ultrawide color gamut in next-generation displays, as is defined by the recommendation (Rec.) 2020 standard. However, because the human eye is more sensitive to the green spectral region, it is not yet possible to achieve an ultrapure green electroluminescence (EL) with a sufficiently narrow bandwidth that covers >95% of the Rec. 2020 standard in the CIE 1931 color space. Here, we demonstrate efficient, ultrapure green EL based on the colloidal two-dimensional (2D) formamidinium lead bromide (FAPbBr) hybrid perovskites. Through the dielectric quantum well (DQW) engineering, the quantum-confined 2D FAPbBr perovskites exhibit a high exciton binding energy of 162 meV, resulting in a high photoluminescence quantum yield (PLQY) of ∼92% in the spin-coated films. Our optimized LED devices show a maximum current efficiency (η) of 13.02 cd A and the CIE 1931 color coordinates of (0.168, 0.773). The color gamut covers 97% and 99% of the Rec. 2020 standard in the CIE 1931 and the CIE 1976 color space, respectively, representing the "greenest" LEDs ever reported. Moreover, the device shows only a ∼10% roll-off in η (11.3 cd A) at 1000 cd m. We further demonstrate large-area (3 cm) and ultraflexible (bending radius of 2 mm) LEDs based on 2D perovskites.

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

“…As a result, the color gamut covers 104% of the Rec. 2020 standard in the CIE 1931 color space, demonstrating the purest green emission ever reported . In terms of the National Television System Committee standard, the color gamut is as high as 123% in the CIE 1931 color space.…”

“…For instance, Kumar et al demonstrated a green LED with 2D formamidinium lead bromide hybrid perovskites, achieving a color gamut covering 96.8% of the Rec. 2020 standard in the CIE 1931 color space, which is the “greenest” LED reported thus far . Using supercrystal inorganic perovskites, Tong et al also reported an LED exhibiting a color close to the Rec.…”

Monochromatic LEDs based on perovskite quantum dots: Opportunities and challenges

“…The characteristics are slightly lower than the bulk perovskite LED devices in which the emission wavelength is difficult to fine tune. We report the operational life time (LT 50 ) at initial luminance of approximately 1000 nits (at 10 mA cm −2 ) to be around 3 hours . Clearly, more work needs to be done to enhance the operational lifetimes in the EL‐based perovskite devices.…”

“…However, OIHP semiconductor NCs can be easily integrated into optoelectronic devices, including the LEDs . In practice, an important motivation for the development of perovskite LEDs is the need of monochromatic light sources covering the entire visible range, in particular in the deep green spectral region, because the human eyes can distinguish more color tones in the green wavelength region . Assuming fixed blue and red primaries in the CIE color coordinates, Figure presents the calculated coverage of Rec.…”

Fast Postmoisture Treatment of Luminescent Perovskite Films for Efficient Light‐Emitting Diodes

“…A precursor solution of methylammonium bromine (MABr) and PbBr 2 with a molar ratio of 3:1 dissolved in dimethylformamide (DMF) was used to deposit luminescent MAPbBr 3 films on the indium tin oxide (ITO) glass substrates with precoated poly(3,4‐ethylenedioxythiophene):polystyre sulfonate (PEDOT:PSS) and poly(9‐vinycarbazole) (PVK) films (glass/ITO/PEDOT:PSS/PVK). A hole transport layer (HTL) such as PVK or poly( N , N ′‐bis(4‐butylphenyl)‐ N , N ′‐bis(phenyl)‐benzidine) (poly‐TPD) was often deposited on PEDOT:PSS for perovskite nanocrystal‐based LEDs to improve the hole injection into luminescent perovskite nanocrystals due to the decreased hole injection energy barrier from the highest occupied molecular orbital level of PEDOT:PSS to the valence band maximum of perovskite nanocrystals. The as‐prepared MAPbBr 3 films were then transferred into humid controllable chamber with a fast postmoisture exposure treatment after annealing in nitrogen glove box.…”