Zhan Chen

Prediction and Design of Efficient Exciplex Emitters for High‐Efficiency, Thermally Activated Delayed‐Fluorescence Organic Light‐Emitting Diodes

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications.

Nearly 100% Triplet Harvesting in Conventional Fluorescent Dopant‐Based Organic Light‐Emitting Devices Through Energy Transfer from Exciplex

Nearly 100% triplet harvesting in conventional fluorophor-based organic light-emitting devices is realized through energy transfer from exciplex. The best C545T-doped device using the exciplex host exhibits a maximum current efficiency of 44.0 cd A(-1) , a maximum power efficiency of 46.1 lm W(-1) , and a maximum external quantum efficiency of 14.5%.

Remanagement of Singlet and Triplet Excitons in Single‐Emissive‐Layer Hybrid White Organic Light‐Emitting Devices Using Thermally Activated Delayed Fluorescent Blue Exciplex

A high-performance hybrid white organic light-emitting device (WOLED) is demonstrated based on an efficient novel thermally activated delayed fluorescence (TADF) blue exciplex system. This device shows a low turn-on voltage of 2.5 V and maximum forward-viewing external quantum efficiency of 25.5%, which opens a new avenue for achieving high-performance hybrid WOLEDs with simple structures.

Novel Carbazol-Pyridine-Carbonitrile Derivative as Excellent Blue Thermally Activated Delayed Fluorescence Emitter for Highly Efficient Organic Light-Emitting Devices

A novel blue thermally activated delayed fluorescence (TADF) emitter, CPC (2,6-di(9H-carbazol-9-yl)-4-phenylpyridine-3,5-dicarbonitrile), was designed and synthesized. By directly linking carbazole (to serve as electron-donor) and pyridine-3,5-dicarbonitrile (to serve as electron-acceptor), and distributing cyanogroups and carbazole groups at the para-position of pyridine core, CPC successfully achieves an extremely small singlet-triplet splitting and fairish photoluminescence quantum yield, thus can act as the highly efficient blue TADF emitter. The optimized organic light-emitting diode (OLED) based on 13 wt % CPC doped in mCP (1,3-bis(9H-carbazol-9-yl)benzene) host exhibits maximum current efficiency, power efficiency, and external quantum efficiency of 47.7 cd A(-1), 42.8 lm W(-1), and 21.2%, respectively, which are the best results in reported blue TADF-based devices up to date and even comparable with the best reported blue phosphorescent OLEDs.

Achieving Highly Efficient Simple-Emission Layer Fluorescence/Phosphorescence Hybrid White Organic Light-Emitting Devices via Effective Confinement of Triplets

Achieving high efficiencies in simple device configurations is a long-standing and meaningful target for organic light-emitting devices (OLEDs). Herein, by utilizing an efficient blue-violet fluorophor (CzS1) that has a high triplet energy of 2.62 eV, the significance of effective confinement of the green triplets in fluorescence/phosphorescence hybrid white devices (F/P-WOLEDs) that have highly simplified emission layers (EMLs) containing only RGB emitters was demonstrated. The non-p-i-n warm-white device exhibited excellent performance with a maximum forward power efficiency high up to 42.1 lm W(-1), and maintaining at 26.3 lm W(1-) at a practical luminance of 1000 cd m(-2).

Multifunctional terpyridine/diphenylamine derivatives as highly efficient blue fluorescent emitters and red phosphorescent hosts

Three terpyridine (TPY)/diphenylamine (DPA) derivatives, with DPA functioning as the electron donor and TPY as the electron acceptor, were designed and synthesized. By switching the position of the nitrogen atom in the substituted pyridine of TPY acceptors, we can adjust the electron-drawing strength of the TPY group, and hence, further modify the fluorescence, lowest unoccupied molecular orbital energy levels, carrier transporting properties of three compounds, but barely influence triplet energy levels. Three compounds satisfy the requirements of multifunctional blue fluorophores and are successfully used as highly efficient blue fluorescent emitters and red phosphorescent hosts in organic light-emitting devices (OLEDs). Non-doped blue fluorescent OLEDs that use TPY22DPA, TPY33DPA, and TPY44DPA as emitters exhibit maximum external quantum efficiencies (EQEs) of 4.9%, 3.8%, and 2.7%, respectively. Meanwhile, red phosphorescent OLEDs that use TPY22DPA, TPY33DPA, and TPY44DPA as host materials exhibit maximum EQEs of 19.1%, 20.9%, and 17.2%, respectively. These results are among the best reported multifunctional blue fluorophore efficiencies.

A high-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor

A new efficient blue fluorophor 4-(4-diphenylaminophenyl)diphenylsulfone (SOTPA), with high triplet energy and balanced charge-transporting properties, has been designed and synthesized, and showed impressive performance both as blue emitter and as a host for phosphors. A green phosphorescent device containing SOTPA as host showed a maximum external quantum efficiency (EQE) as high as 19.2%, suggesting almost complete triplet harvesting from the blue fluorophor by the green phosphor. Single-emitting layer (EML) F–P hybrid white organic light-emitting devices (WOLEDs) based on SOTPA also gave outstanding electroluminescence performance, with a low turn-on voltage of 2.7 V and maximum EQE and power efficiency (PE) of 15.4% and 40.2 lm W−1, respectively. Even at a practical brightness of 1000 cd m−2 the PE still remained as high as 24.1 lm W−1. This excellent performance represents the highest efficiency yet reported among single-EML F–P hybrid WOLEDs.

Self-Assembly of Electron Donor–Acceptor-Based Carbazole Derivatives: Novel Fluorescent Organic Nanoprobes for Both One- and Two-Photon Cellular Imaging

In this study, we report fluorescent organic nanoprobes with intense blue, green, and orange-red emissions prepared by self-assembling three carbazole derivatives into nanorods/nanoparticles. The three compounds consist of two or four electron-donating carbazole groups linked to a central dicyanobenzene electron acceptor. Steric hindrance from the carbazole groups leads to noncoplanar 3D molecular structures favorable to fluorescence in the solid state, while the donor-acceptor structures endow the molecules with good two-photon excited emission properties. The fluorescent organic nanoprobes exhibit good water dispersibility, low cytotoxicity, superior resistance against photodegradation and photobleaching. Both one- and two-photon fluorescent imaging were shown in the A549 cell line. Two-photon fluorescence imaging with the fluorescent probes was demonstrated to be more effective in visualizing and distinguishing cellular details compared to conventional one-photon fluorescence imaging.

A novel nicotinonitrile derivative as an excellent multifunctional blue fluorophore for highly efficient hybrid white organic light-emitting devices

A novel nicotinonitrile derivative CZN has been designed with the aim of developing excellent multifunctional blue fluorophores for hybrid white organic light-emitting devices (WOLEDs) by introducing the nicotinonitrile group as the electron acceptor. CZN shows highly efficient blue fluorescence and its non-doped blue OLED delivers an external quantum efficiency (EQE) as high as 4.6%. Meanwhile, CZN is a promising host for phosphorescent OLEDs, realizing high EQEs of 22.8%, 24.8% and 19.9% for yellow, orange and deep-red phosphorescence, respectively. By using CZN as the blue emitter and the host simultaneously, a hybrid white OLED has been achieved with a forward-viewing EQE of 17.2%. These results indicate that the nicotinonitrile unit is an excellent building block for developing new multifunctional compounds as both blue fluorescent emitters and phosphorescent hosts for efficient hybrid WOLEDs.

Organic Light-Emitting Devices: Remanagement of Singlet and Triplet Excitons in Single-Emissive-Layer Hybrid White Organic Light-Emitting Devices Using Thermally Activated Delayed Fluorescent Blue Exciplex (Adv. Mater. 44/2015)

On page 7079, X.-H. Zhang, C.-S. Lee, and co-workers discuss the drawbacks of single-emitting-layer hybrid white organic light-emitting devices (WOLEDs) based on conventional fluorescent hosts, and demonstrate an effective way to overcome these drawbacks by using the thermally activated delayed fluorescent blue exciplex. Based on this new concept, high-efficiency WOLEDs with a forward-viewing power efficiency of 48.7 lm W(-1) at 100 cd m(-2) are achieved.