Ultrathin Emissive Layer Research Articles

Highly Simplified Tandem Organic Light-Emitting Devices Incorporating a Green Phosphorescence Ultrathin Emitter within a Novel Interface Exciplex for High Efficiency.

Herein we report a novel design philosophy of tandem OLEDs incorporating a doping-free green phosphorescent bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) (Ir(ppy)2(acac)) as an ultrathin emissive layer (UEML) into a novel interface-exciplex-forming structure of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 1,3,5-tri(p-pyrid-3-yl-phenyl)benzene (TmPyPB). Particularly, relatively low working voltage and remarkable efficiency are achieved and the designed tandem OLEDs exhibit a peak current efficiency of 135.74 cd/A (EQE = 36.85%) which is two times higher than 66.2 cd/A (EQE = 17.97%) of the device with a single emitter unit. This might be one of the highest efficiencies of OLEDs applying ultrathin emitters without light extraction. Moreover, with the proposed structure, the color gamut of the displays can be effectively increased from 76% to 82% NTSC if the same red and blue emissions as those in the NTSC are applied. A novel form of harmonious fusion among interface exciplex, UEML, and tandem structure is successfully realized, which sheds light on further development of ideal OLED structure with high efficiency, simplified fabrication, low power consumption, low cost, and improved color gamut, simultaneously.

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

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.

Efficient non-doped monochrome and white phosphorescent organic light-emitting diodes based on ultrathin emissive layers

Efficient red, orange, green and blue monochrome phosphorescent organic light-emitting diodes (OLEDs) with simplified structure were fabricated based on ultrathin emissive layers. The maximum efficiencies of red, orange, green and blue OLEDs are 19.3cd/A (17.3lm/W), 45.7cd/A (43.2lm/W), 46.3cd/A (41.6lm/W) and 11.9cd/A (9.2lm/W). Moreover, efficient and color stable white OLEDs based on two complementary colors of orange/blue, three colors of red/orange/blue, and four colors of red/orange/green/blue were demonstrated. The two colors, three colors and four colors white OLEDs have maximum efficiencies of 30.9cd/A (27.7lm/W), 30.3cd/A (27.2lm/W) and 28.9cd/A (26.0lm/W), respectively. And we also discussed the emission mechanism of the designed monochrome and white devices.

Balanced white organic light-emitting diode with non-doped ultra-thin emissive layers based on exciton management

The non-doped ultra-thin emissive layer (EML) is a promising novel structure for fabricating organic light-emitting diodes (OLEDs). We attempt to perform exciton management in order to obtain a highly efficient and balanced light-emitting phosphorescent red–green–blue (RGB) white OLED (WOLED). These studies include optimization of the locations of the three RGB EMLs based on investigations concerning the spatial distribution of excitons, along with the energy transfer mechanisms between different materials. More importantly, by introducing a 1,1-bis((di-4-tolylamino)phenyl) cyclohexane (TAPC) interlayer, which acts as a hole-trapping layer, a redistribution of excitons is realized, giving rise to a more balanced white light emission. This simple method is an efficient way to adjust the exciton distribution, and could therefore be used in future OLED devices.

52.3: Exciton Management in Non‐doped Ultra‐thin Emissive Layers Based Organic Light‐Emitting Diodes

Non‐doped ultrathin emissive layer based OLED is demonstrated to be a promising novel structure to stimulate two‐color dual emission through exciton management. By using a ultra‐thin TAPC interlayer as a hole‐trapping layer, exciton redistribution is realized and dual emission are observed without using any doped layers. The mechanism of this trapping interlayer is further discussed.

Doping-free orange and white phosphorescent organic light-emitting diodes with ultra-simply structure and excellent color stability

We demonstrate simplified doping-free orange phosphorescent organic light-emitting diodes (OLEDs) based on ultrathin emission layer. The optimized orange device has the maximum current efficiency of 52.1cd/A and power efficiency of 36.3lm/W, respectively. Efficient simplified doping-free white OLEDs employing blue and orange ultrathin emission layers have excellent color stability, which is attributed to the avoidance of the movement of charges recombination zone and no differential color aging. One white device exhibits high efficiency of 33.6cd/A (30.1lm/W). Moreover, the emission mechanism of doping-free orange and white OLEDs is also discussed.

Improved performance for white phosphorescent organic light-emitting diodes utilizing an orange ultrathin non-doped emission layer

The chemical structures of materials, the device structures (a) and the detailed energy level diagram of the materials (b).

Ultrathin emissive layers

Ultrathin emissive layers

Efficient light emitting devices based on phosphorescent partially doped emissive layers

We report efficient organic light emitting devices employing an ultrathin phosphor emissive layer. The electroluminescent spectra of these devices can be tuned by introducing a low-energy emitting phosphor layer into the emission zone. Devices with the emissive layer consisting of multiple platinum-complex/spacer layer cells show a peak external quantum efficiency of 18.1%, which is among the best EQE values for platinum-complex based light emitting devices. Devices with an ultrathin phosphor emissive layer show stronger luminance decay with the operating time compared to the counterpart devices having a host–guest emissive layer.

Doubling Coupling-Out Efficiency in Organic Light-Emitting Devices Using a Thin Silica Aerogel Layer

An innovative way of enhancing the coupling-out efficiency in light-emitting diodes (LEDs) is revealed. A very low-refractive-index silica aerogel is placed between the substrate and the emissive layer to obtain a perfect decoupling of the propagation modes within the emissive layer from the glass substrate. The Figure shows an ultrathin emissive layer on a glass substrate with (left) and without (right) an aerogel spacer layer under UV irradiation (see also cover).