Solution‐Processed Extremely Efficient Multicolor Perovskite Light‐Emitting Diodes Utilizing Doped Electron Transport Layer

Abstract

A specially designed n‐type semiconductor consisting of Ca‐doped ZnO (CZO) nanoparticles is used as the electron transport layer (ETL) in high‐performance multicolor perovskite light‐emitting diodes (PeLEDs) fabricated using an all‐solution process. The band structure of the ZnO is tailored via Ca doping to create a cascade of conduction energy levels from the cathode to the perovskite. This energy band alignment significantly enhances conductivity and carrier mobility in the CZO ETL and enables controlled electron injection, giving rise to sub‐bandgap turn‐on voltages of 1.65 V for red emission, 1.8 V for yellow, and 2.2 V for green. The devices exhibit significantly improved luminance yields and external quantum efficiencies of, respectively, 19 cd A−1 and 5.8% for red emission, 16 cd A−1 and 4.2% for yellow, and 21 cd A−1 and 6.2% for green. The power efficiencies of these multicolor devices demonstrated in this study, 30 lm W−1 for green light‐emitting PeLED, 28 lm W−1 for yellow, and 36 lm W−1 for red are the highest to date reported. In addition, the perovskite layers are fabricated using a two‐step hot‐casting technique that affords highly continuous (>95% coverage) and pinhole‐free thin films. By virtue of the efficiency of the ETL and the uniformity of the perovskite film, high brightnesses of 10 100, 4200, and 16,060 cd m−2 are demonstrated for red, yellow, and green PeLEDs, respectively. The strategy of using a tunable ETL in combination with a solution process pushes perovskite‐based materials a step closer to practical application in multicolor light‐emitting devices.

Photo-Controlled Nano-Supramolecular Size and Reversible Luminescent Behaviors Based on Cucurbit[7]uril Cascaded Assembly

“…It was consistent with our assumption t h a t t h e fl u o r e s c e n c e l i f e t i m e o f O F -D A E -CO⊂CB [7] 2 &HACD at λ = 540 nm became shorter after exposure to 254 nm (1.27 ns) but longer after >600 nm illumination (1.58 ns) than the initial value (1.45 ns) (Figure 3c, Table S1). In addition, CF-DAE-CO⊂CB [7] 2 and CF-DAE-CO⊂CB [7] 2 &HACD exhibited an obvious Tyndall effect (Figure S6), indicating the formation of larger aggregates. Accordingly, the aforementioned phenomena altogether indicated that light could cause the aggregation of our assemblies.…”

“…The 2D ROESY spectrum also showed significant NOE cross-peaks between DAE-CO⊂CB [7] To our excitement, when OF-DAE-CO⊂CB [7] 2 and OF-DAE-CO⊂CB [7] 2 &HACD were irradiated with UV light of 254 nm, peaks at 331 and 380 nm decreased but that at 273 nm increased. Meanwhile, a new absorption at 680 nm emerged, accompanied by the appearance of two isosbestic points (317 and 427 nm) (Figure 4), indicating the production of supramolecular assemblies in the closed form (CF-DAE-CO⊂CB [7] 2 and CF-DAE-CO⊂CB [7] 2 &HACD). When the assemblies were subsequently irradiated with >600 nm light, the UV−vis absorption spectra of CF-DAE-CO⊂CB [7] 2 and CF-DAE-CO⊂CB [7] 2 &HACD could not recover to their original levels with the position of the absorption peaks unchanged but the absorption intensity decreased.…”

“…Therefore, by using a nonlinear leastsquares curve-fitting method, the association constant (K a ) was calculated to be 3.49 × 10 9 M −2 (Figure S12) by analyzing the sequential changes in the absorption intensity of DAE-CO at 383 nm in the presence of varying concentrations of CB [7], which was comparable to the reported K a value between CB [7] and coumarin salt. 51 Furthermore, in 1 H NMR spectra of DAE-CO with varying concentrations of CB [7] (Figure S13), peaks of free DAE-CO totally disappeared when 2.0 equiv of CB [7] was added, further implying an ideal host−guest binding ratio. As shown in Figure 2, the chemical shifts of protons (H1, H3, H4, and H5) residing on the coumarin groups, methylene (H6), and those (H7) on the pyridine groups presented upfield shifts (Δδ = 0.64, 1.02, 1.07, 0.76, 0.53, and 0.44 ppm for H1, H3, H4, H5, H6, and H7, respectively).…”

Improved Efficiency of Perovskite Light-Emitting Diodes Using a Three-Step Spin-Coated CH3NH3PbBr3 Emitter and a PEDOT:PSS/MoO3-Ammonia Composite Hole Transport Layer

“…The effect of the small MoO 3 -ammonia amount on the surface morphology of CH 3 NH 3 PbBr 3 film is not evident. As reported in the literature, multi-step spin coating is expected to improve the surface morphology of perovskite film [27,28]. As shown in Figure 2, uniform and compact perovskite films with enhanced crystallinity formed on increasing the coating times from one to three.…”

Ligand Engineering of Ultrasmall CsPbI 3 Quantum Dots via In Situ S N 2 Substitution Enables Bright Rec. 2020 Pure‐Red Perovskite LEDs with Exceptional Current Efficiency

“…More importantly, because of the saturated red emission and exceptional luminance of the devices, we achieved a record-breaking CE of 20.73 cd A -1 . The achievement outperforms state-of-the-art red-emissive PeLEDs utilizing poly-crystalline thin films and also colloidal QDs (Figure S17 and Tables S2 andS3) and is comparable with that of best-performing organic-based pure-red LEDs showing a CE of 20.2 cd A -1 with a peak EQE of over 30% [19,30,[44][45][46][47][48][49][50][51]. In addition, we found that pure-red PeLEDs fabricated from CsPbI 3 QDs synthesized with alkyl iodides with varied chain lengths (C4, C6, and C10) and diiodooctane all achieved simultaneously enhanced EQE, luminance, and CE, indicating the universal beneficial effects of our in situ ligand modification strategy based on the S N 2 reaction in improving the performance parameters of ensuing electroluminescent devices (Figures S18 andS19).…”