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.
Colloidal
perovskite nanocrystals are emerging as one of the most
promising candidates for next-generation monochromatic light sources
that require precise bandgap tunability. However, the current efficiency
(ηCE) and operational lifetime in their light-emitting
diodes (LEDs) remain low due to impeded carrier transport and exciton
quenching through the NC ligand layer. Here, we show that the fundamental
limitation can be overcome in the superstructures containing polydisperse
colloidal quantum wells of organic–inorganic hybrid perovskites.
The mixing entropy-induced layering polydispersity promotes the delayed
radiative energy transfer (DRET) that guides exciton transport with
negligible nonradiative losses, boosting the thin-film photoluminescence
quantum yield >96%. By using the superstructures in LEDs, we report
a ηCE of 30.4 cd A–1, with an operational
lifetime (LT50) of 184 min at a high constant driving current
of 10 mA cm–2. These are among the most high-performance
colloidal perovskite nanocrystals LEDs ever demonstrated.
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