Manipulation of Charge and Exciton Distribution Based on Blue Aggregation‐Induced Emission Fluorophors: A Novel Concept to Achieve High‐Performance Hybrid White Organic Light‐Emitting Diodes

Abstract

The aggregation-induced emission (AIE) phenomenon is important in organic light-emitting diodes (OLEDs), for it can potentially solve the aggregationcaused quenching problem. However, the performance of AIE fl uorophorbased OLEDs (AIE OLEDs) is unsatisfactory, particularly for deep-blue devices (CIEy < 0.15). Here, by enhancing the device engineering, a deep-blue AIE OLED exhibits low voltage (i.e., 2.75 V at 1 cd m −2 ), high luminance (17 721 cd m −2 ), high effi ciency (4.3 lm W −1 ), and low effi ciency roll-off (3.6 lm W −1 at 1000 cd m −2 ), which is the best deep-blue AIE OLED. Then, blue AIE fl uorophors, for the fi rst time, have been demonstrated to achieve high-performance hybrid white OLEDs (WOLEDs). The two-color WOLEDs exhibit i) stable colors and the highest effi ciency among pure-white hybrid WOLEDs (32.0 lm W −1 ); ii) stable colors, high effi ciency, and very low effi ciency roll-off; or iii) unprecedented effi ciencies at high luminances (i.e., 70.2 cd A −1 , 43.4 lm W −1 at 10 000 cd m −2 ). Moreover, a three-color WOLED exhibits wide correlated color temperatures (10 690-2328 K), which is the fi rst hybrid WOLED showing sunlight-style emission. These fi ndings will open a novel concept that blue AIE fl uorophors are promising candidates to develop high-performance hybrid WOLEDs, which have a bright prospect for the future displays and lightings.

Emergence of Nanoplatelet Light-Emitting Diodes

“…In LEDs, EQE, power efficiency (PE) and emission color can be used to analyze the performance. For EQE, it can be described below [70,71,72]:$\mathrm{EQE}={\eta }_{out}·r·q·\gamma$ in which η out represents an outcoupling factor, r represents a fraction of excitons that will radiatively decay potentially, q represents a PLQY of emitters, while γ represents a charge balance. According to the classical ray model, η out is only about 0.2.…”

“…The relation for PE and EQE is defined below, if we assumed an emission pattern is Lambertian type, [72]:$\mathrm{PE}\propto \frac{\mathrm{EQE}}{U}$ in which U represents voltages. Hence, low U while high EQE is conducive to achieve high PE.…”

Managing excitons for high performance hybrid white organic light-emitting diodes by using a simple planar heterojunction interlayer

“…[1][2][3][4][5][6][7][8][9][10] In a standard hybrid white organic light-emitting diode (WOLED), the singlet and triplet excitons can be used by fluorescent and phosphorescent materials, respectively, which can theoretically achieve 100% internal quantum efficiency (IQE). However, a blue fluorescent emitting layer (EML) needs to be close to the exciton recombination zone, because the diffusion length of singlet excitons is far below that of triplet excitons.…”

“…In order to alleviate this negative effect, a kind of functional layer called interlayer has been employed in conventional hybrid WOLEDs. 8,15,[18][19][20][21][22][23][24][25] A single hole or electron transport layer can work as a simplest interlayer, 8,[19][20][21][22] which is easy to fabricate but cannot simultaneously provide sufficient blue emission by separating the fluorescent EML from the exciton recombination zone. Quenching can also occur in the triplet transfer process from the exciton recombination zone to the fluorescent emitter with a lower lying non-radiative triplet level.…”

“…8,15,18,[23][24][25] The mixed interlayer can effectively prevent triplet quenching in a fluorescent emitter. Nevertheless, the proportions and the thicknesses of such a mixed interlayer have to be precisely controlled, which renders the device fabrication process both cumbersome and difficult to reproduce.…”