Highly Efficient Quasi-2D Perovskite Light-Emitting Diodes Incorporating a TADF Dendrimer as an Exciton-Retrieving Additive

Abstract

Although small organics or polymer additives have been introduced to enhance film formation and radiative recombination of perovskite light-emitting diodes (PeLEDs), the exciton utilization and quantum efficiency need further optimization. Here, we introduce a thermal-activated delayed fluorescence (TADF) dendrimer as an additive to enhance the surface coverage and reduce the trap state of the grain boundary. More importantly, the TADF nature of such an additive can retrieve the exciton dissociated from perovskite or trapped by the grain boundary and then transfer the energy back to emissive perovskite through the Förster energy transfer process. Since the triplets can be reused by reverse intersystem crossing in such a TADF additive, the theoretical exciton utilization is 100%. As a result, the optimized PeLEDs cooperating with a TADF additive achieved a high current efficiency of 39.0 cd A–1 and an ultrabright luminescence of 18,000 cd m–2, which are almost 5 times higher than those of the control device without an additive. Moreover, the device stability monitored by half-lifetime at 1000 cd m–2 enhanced 2 times after introducing the TADF dendrimer as an additive. The parent dendrimer without a TADF feature was also synthesized as an additive to explore the mechanism action, which found that 54% enhancement of device efficiency can be attributed to defect passivating, while 46% was assigned to retrieved energy. This research first demonstrates that the TADF dendrimer is a promising exciton-retrieving additive for enhancing the performance of PeLEDs by passivating defect, filling up grain boundary, and retrieving leakage exciton.

Thermally Activated Delayed Fluorescence from Perovskite‐Derivative CsAgCl2 Nanocrystals for High‐Resolution X‐Ray Imaging

“…[14][15][16] Although this mechanism can be commonly observed in metal-organic complexes and organic molecules with metal-to-ligand charge transfer (MLCT) or intramolecular charge transfer, it is extremely rare in halide perovskites and their derivatives. [10,11,13,17,18] Most recently, vacancy-ordered zirconium-based double perovskites are observed to exhibit the strong TADF emission with a 70% PLQY and set off a new wave of research for TADF in perovskites. [16,[19][20][21][22] However, aside from this kind of materials, no other perovskite-type material with TADF emission has been reported by scholars and researchers up to now, which severely limits the understanding of the underlying origin of TADF emission and the relationship between crystal structure and luminescence mechanism in perovskites.…”

“…[ 14–16 ] Although this mechanism can be commonly observed in metal–organic complexes and organic molecules with metal‐to‐ligand charge transfer (MLCT) or intramolecular charge transfer, it is extremely rare in halide perovskites and their derivatives. [ 10,11,13,17,18 ]…”

Energy and Charge Dual Transfer Engineering for High‐Performance Green Perovskite Light‐Emitting Diodes

“…Therefore, to maximize device performance, it is essential to exploit FRET‐mediated exciton transfer, in addition to enhancing the direct recombination of perovskite EMLs. [ 18,19 ]…”

“…Therefore, to maximize device performance, it is essential to exploit FRET-mediated exciton transfer, in addition to enhancing the direct recombination of perovskite EMLs. [18,19] In this study, for the first time, a fluorescent and phosphorescent 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP)-based novel co-HTL was introduced into the device to harvest additional excitons produced via FRET to enhance the PeLED…”

Mixed-halide copper-based perovskite R2Cu(Cl/Br)4 with different organic cations for reversible thermochromism

“…Hybrid perovskites with two-dimensionality (2D) have made considerable advances as optoelectronic materials for photovoltaic, 1,2 X-ray detection, [3][4][5][6][7][8] light-emitting, [9][10][11][12][13][14][15] spintronic, 16,17 photodetection, [18][19][20][21][22][23] lasing, [24][25][26][27][28][29] and other applications. [30][31][32][33][34] Due to their high chemical stability and photostability and the facile diversity of their organic and inorganic cations, halide anions, and metal cations, 2D-perovskites have emerged as an ideal platform for novel functional semiconductors.…”