Highly Efficient Perovskite Nanocrystal Light‐Emitting Diodes Enabled by a Universal Crosslinking Method

Abstract

presence of aliphatic ligands. [ 7 ] These perovskite nanocrystals are highly luminescent and emit over the full visible range, making them ideal candidates for luminescent display applications. [ 6 ] The synthetic steps are generally straightforward, and the easy control of halide content allows the perovskite bandgaps to be tailored, both by chemical compositions as well as by quantum size effects. So far, perovskite nanocrystals are shown to have color-pure emission, close to unity photoluminescence yield and low lasing thresholds. [ 8 ] These nanocrystals were also attempted in light-emitting devices, but effi ciencies remain modest at 0.12%. [ 9 ] Here, we show the preparation of highly effi cient perovskite light-emitting diodes (PeLED) using solution-processed nanocrystals. We apply a new trimethylaluminum (TMA) vapor-based crosslinking method to render the nanocrystal fi lms insoluble, thereby allowing the deposition of subsequent charge-injection layers without the need for orthogonal solvents. The resulting near-complete nanocrystal fi lm coverage, coupled with the natural confi nement of injected charges within the perovskite crystals, facilitate electron-hole capture and give rise to a remarkable electroluminescence yield of 5.7%. Here, our electron-injection layer comprises a fi lm of zinc oxide (ZnO) nanocrystals, directly deposited on an indium tin oxide (ITO)-coated glass substrate. [ 4 ] The cesium lead halide nanocrystals were solution-coated onto the ZnO fi lm as the emissive layer. Due to the presence of aliphatic ligands on the nanocrystals, the perovskite fi lm remains soluble to organic solvents, which limits the deposition of subsequent chargeinjection layers using solution methods. We employed a new TMA vapor-phase crosslinking technique to fi x the nanocrystal fi lm in place, thereby enabling us to solution-cast a layer of TFB polymer (poly[(9,9-dioctylfl uorenyl-2,7-diyl)-co -(4,4′-( N -(4-sec-butylphenyl)diphenylamine)]) above without washing the nanocrystals off. TFB serves primarily as a hole-injection and electron-blocking layer. A thin, high work-function molybdenum trioxide (MoO 3 ) interlayer and silver electrode were vacuum-thermal evaporated to complete the device.As shown in Figure 1 c,d, our perovskite nanocrystal devices show saturated and color-pure emission. We control the perovskite bandgap, primarily by tailoring the halide composition, and achieve electroluminescence across a wide range of the visi ble spectrum. Our red, orange, green, and blue devices emit at wavelengths of 698, 619, 523, and 480 nm, respectively.

Colloidal lead halide perovskite nanocrystals: synthesis, optical properties and applications

“…The additional perfluorinated ionomer layer both increased the hole injection efficiency of the device and suppressed the charging of the emissive layer, leading to a threefold increase in the peak brightness reaching 1377 cd m − 2 . Li et al 113 reported on LEDs comprising large (roughly 20 nm) square-shaped NCs with an electroluminescence QY of 5.7% using a device structure of glass/ITO/ZnO/CsPbX 3 QDs/ TFB polymer (poly[(9,9-dioctylfl uorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl) diphenylamine)])/MoO 3 (molybdenum trioxide)/Ag. Manna and colleagues 114 incorporated inorganic halide perovskite NCs of varying morphology (cubes and platelets) and halide composition (bromide and iodide) into white-light-emitting perovskite LEDs.…”

High Open‐Circuit Voltages in Tin‐Rich Low‐Bandgap Perovskite‐Based Planar Heterojunction Photovoltaics

“…[12][13][14][15][16][17] The vast majority of research conducted in this area has focused on "first generation" MAPbX 3 -based perovskites, [8,18] mainly due to the excellent tunability of their optoelectronic properties. [18,19] Characteristics such as high mobility, [20,21] high bimolecular recombination rate for charge carriers, [10] and low exciton binding energy [22][23][24] have resulted in the demonstration of high-performance films and devices for PV, LED, [9,12,[25][26][27] FET, [21] and lasing applications. [10,28] One potential drawback of the MAPbX 3 semiconductor family, however, is its relatively wide bandgap (3.2-1.6 eV), which dramatically limits its sensitivity in the near-IR (NIR) to mid-IR region of the solar spectrum.…”

Research Update: Challenges for high-efficiency hybrid lead-halide perovskite LEDs and the path towards electrically pumped lasing

“…With these crystals, full-colour PeLEDs can be fabricated, and their photograph and emission spectra are shown in Figure 3(c). 30,39,40 After the report of Protesescu et al, Zhang et al reported the synthesis of organic-inorganic hybrid perovskite quantum dots with PLQEs up to 70% and demonstrated the application of them as an alternative phosphor for white-light LEDs. 41 Afterwards various synthesis routes have been reported.…”