Highly Efficient White Organic Light-Emitting Diodes with Ultrathin Emissive Layers and a Spacer-Free Structure

Abstract

Ultrathin emissive layers (UEMLs) of phosphorescent materials with a layer thickness of less than 0.3 nm were introduced for high-efficiency organic light-emitting diodes (OLEDs). All the UEMLs for white OLEDs can be prepared without the use of interlayers or spacers. Compared with devices fabricated with interlayers inserted in-between the UEMLs, our spacer-free structure not only significantly improves device efficiency, but also simplifies the fabrication process, thus it has a great potential in lowering the cost of OLED panels. In addition, its spacer-free structure decreases the number of interfaces which often introduce unnecessary energy barriers in these devices. In the present work, UEMLs of red, green and blue-emitting phosphorescent materials and yellow and blue phosphorescent emitters are utilized for the demonstration of spacer-free white OLEDs. Upon optimization of the device structure, we demonstrated spacer-free and simple-structured white-emitting OLEDs with a good device performance. The current and power efficiencies of our white-emitting devices are as high as 56.0 cd/A and 55.5 lm/W, respectively. These efficiencies are the highest ever reported for OLEDs fabricated with the UEML approach.

Manipulation and exploitation of singlet and triplet excitons for hybrid white organic light-emitting diodes with superior efficiency/CRI/color stability

“…This is because a 0−3 nm-thick TCTA or TPBi layer should not form a complete film, 35,37 where many unoccupied sites exist in film. 38 Although the triplet energy levels of TCTA (2.80 eV) and TPBi (2.70 eV) are higher than that of Bepp 2 (2.60 eV), the triplet excitons generated in Bepp 2 EML should also penetrate a x(0-3) nm-thick TCTA and TPBi layers via unoccupied sites due to a long exciton diffusion distance (> 10 nm) 4,7, 29,39 and further transfer energy to Ir(ffpmq) 2 (acac) by Dexter energy transfer for yellow emission, inducing a high utilization rate of excitons. And combined with blue emission from Bepp 2 , it is expected that white emission can be obtained.…”

High-efficiency/CRI/color stability warm white organic light-emitting diodes by incorporating ultrathin phosphorescence layers in a blue fluorescence layer

“…These devices were named as device W1 for the incorporation with red/ yellow/green sequence, device W2 for the incorporation with green/yellow/red sequence, device W3 for the incorporation with green/red/yellow sequence, and device W4 for the incorporation with yellow/red/green sequence. The detailed device structures are listed below: Here, ultrathin sheets of phosphors with a thickness of <0.1 nm do not form a neat layer but partially penetrate into the adjacent Bepp 2 [33,34]; hence, they serve as dopants in adjacent Bepp 2 . In addition, in these white devices, different-color ultrathin phosphorescence layers are incorporated away from HTL/EML and EML/ETL interfaces for 3 nm, and they are also separated by a 2 nm-thick Bepp 2 layer.…”

High Efficiency Non‐Doped White Organic Light Emitting Diodes Based on a Bilayer Interface‐Exciplex Structure

“…Correspondingly, the EQE increases and the device W14 with 3‐nm‐thick PO‐T2T interlayer shows a maximum EQE of 20.0% and 17.6% at luminance of 1000 cd m −2 (Figure b). The EQE of white device is lower than that of blue device, which may be due to the higher luminous efficiency of blue emission than that of orange‐red . However, the WOLED with this structure shows poor color stability.…”