High-efficiency blue-emission crystalline organic light-emitting diodes sensitized by “hot exciton” fluorescent nanoaggregates

Abstract

Sensitizing fluorescent materials is an effective way to maximally use excitons and obtain high-efficiency blue organic light-emitting diodes (OLEDs). However, it is a persistent challenge for present amorphous thin-film OLEDs to improve photon emission under low driving voltage, severely impeding the development of OLED technology. Here, we propose a novel OLED architecture consisting of a crystalline host matrix (CHM) and embedded “hot exciton” nanoaggregates (HENAs), which effectively sensitize blue dopant (D) emission. Owing to the advantages of the crystalline thin-film route, the device exhibits largely enhanced blue photon output [Commission International de L’Eclairage coordinates of (0.15, 0.17)], with a low turn-on/operation voltage of 2.5 V (at 1 cd/m 2 )/3.3 V (at 1000 cd/m 2 ), an extremely low Joule heat loss ratio (7.8% at 1000 cd/m 2 ), and a maximum external quantum efficiency (EQE) up to 9.14%. These areal photon output features have outperformed the present amorphous thin-film blue OLEDs with high EQE, demonstrating that the CHM-HENA-D OLED is promising for future OLEDs.

High‐Efficiency Blue‐Emission Crystalline Organic Light‐Emitting Diodes by Engineering Thermally Activated Delayed Fluorescence Nanoaggregates

“…Additionally, although a typical material system of MADN: DSA‐Ph (3 wt%) was used to fabricate a long‐lifetime blue OLED (T 1/2 = 46 000 h), [ 50 ] it shows evident molecular aggregates and “pinholes” within 20 h at Condition 1 and 20 min at Condition 2. [ 27 ] These results demonstrated superior stability of the CHM‐TADFNA thin film and their potential in realizing OLED with high operational stability.…”

“…However, the four devices exhibit comparable current densities, although the device with an NDT of 3.0 nm exhibits a relatively low current density. Based on our previous study, [ 27 ] it was demonstrated that the CHM is the pathway for hole transportation. On the other hand, electrons are directly injected from the cathode due to the deep LUMO of DMAC‐DPS nanoaggregates.…”

“…The top parts of nanoaggregates exposed out of the film surface can facilitate the direct injection of electrons from the electron transport layer into nanoaggregates. [ 27 ] At the same time, the hole carriers injected from the anode pass through the high mobility BP1T/2FPPICz crystalline layers and then encounter the electrons at DMAC‐DPS nanoaggregates. It should be noted that the CHM‐TADFNA structure system can be expanded to include TADF materials, further enhancing the utilization of excitons.…”

“…[22,23] A crystalline host matrix (CHM) with embedded nanoaggregates (NA) is a strategy that combines fixed crystallized host material and various highexciton-utilization-efficiency guests. [27] Guest material nanoaggregates can grow on surface of ordered crystalline thin film, thereby leaving relatively flat areas where further growth of crystalline thin films can occur. Therefore, CHM-NA structure can offer both the advantages of crystallized and high-efficiency materials, i.e., CHM can provide a channel of high carrier mobility while amorphous nanoaggregates emitters can achieve efficient luminescence.…”

Modeling the impacts of energetic disorder and charge transport on the exciton formation zone in organic light-emitting diodes

“…Organic light-emitting diodes (OLEDs) have received tremendous attention since the first demonstration of double-layer structure [1][2][3][4][5][6][7][8][9][10][11][12][13], due to their attractive properties such as light weight, self-emission with highquality color, and availability for fabricating high-resolution display panel. The current level of OLEDs stability at the luminance of ∼2000 cd m −2 enables the successful applications of OLEDs in the important intermissive display fields, e.g., smart phones and watches.…”