Xingwu Yan

Highly efficient red OLEDs using DCJTB as the dopant and delayed fluorescent exciplex as the host

In this manuscript, we demonstrated a highly efficient DCJTB emission with delayed fluorescent exciplex TCTA:3P-T2T as the host. For the 1.0% DCJTB doped concentration, a maximum luminance, current efficiency, power efficiency and EQE of 22,767 cd m−2, 22.7 cd A−1, 21.5 lm W−1 and 10.15% were achieved, respectively. The device performance is the best compared to either red OLEDs with traditional fluorescent emitter or traditional red phosphor of Ir(piq)3 doped into CBP host. The extraction of so high efficiency can be explained as the efficient triplet excitons up-conversion of TCTA:3P-T2T and the energy transfer from exciplex host singlet state to DCJTB singlet state.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Improvement of both efficiency and working lifetime in organic photovoltaic devices by using bathophenanthroline/tin(IV) phthalocyanine dichloride as bilayer exciton blocking layers

We demonstrate that the improvement of both efficiency and lifetime of organic photovoltaic (OPV) devices by employing thinner bathophenanthroline (Bphen) and thicker tin(IV) phthalocyanine dichloride (SnCl2Pc) as the bilayer exciton blocking layers (EBLs), where Bphen and SnCl2Pc acts as the photogenerated exciton blocking layer and optical spacer, respectively. The thicker SnCl2Pc layer can be adopted due to its high electron mobility and aligned lowest unoccupied molecular orbital with the acceptor. The OPV device with such a bilayer EBL leads to an increase by 27% in power conversion efficiency compared to the device with a traditional bathocuproine EBL. Moreover, the lifetime is also improved due to the superior oxygen and moisture diffusion blocking effect of the thick SnCl2Pc layer. The operation mechanism for the improvement in PCE and lifetime was also discussed.

Interface Engineering of Organic Schottky Barrier Solar Cells and Its Application in Enhancing Performances of Planar Heterojunction Solar Cells.

In this work, we describe the performance of organic Schottky barrier solar cells with the structure of ITO/molybdenum oxide (MoOx)/boron subphthalocyanine chloride (SubPc)/bathophenanthroline (BPhen)/Al. The SubPc-based Schottky barrier solar cells exhibited a short-circuit current density (Jsc) of 2.59 mA/cm2, an open-circuit voltage (Voc) of 1.06 V, and a power conversion efficiency (PCE) of 0.82% under simulated AM1.5 G solar illumination at 100 mW/cm2. Device performance was substantially enhanced by simply inserting thin organic hole transport material into the interface of MoOx and SubPc. The optimized devices realized a 180% increase in PCE of 2.30% and a peak Voc as high as 1.45 V was observed. We found that the improvement is due to the exciton and electron blocking effect of the interlayer and its thickness plays a vital role in balancing charge separation and suppressing quenching effect. Moreover, applying such interface engineering into MoOx/SubPc/C60 based planar heterojunction cells substantially enhanced the PCE of the device by 44%, from 3.48% to 5.03%. Finally, we also investigated the requirements of the interface material for Schottky barrier modification.

High efficient white organic light-emitting diodes based on triplet multiple quantum well structure

We demonstrate the high efficient triplet multiple quantum well (MQW) structure white organic light-emitting diodes (WOLEDs) (MQW-WOLEDs) by introducing phosphorescent Ir-complex material. In the triplet MQW-WOLEDs, 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene functions as the potential barrier layer; fluorescent dopant layer and Ir-complex phosphorescent dopant layer act as the blue-emitting and orange-emitting potential well layer, respectively. The maximum luminance, current efficiency, and power efficiency are 19 000 cd/m2, 14.5 cd/A, and 5.4 lm/W, respectively; and the efficiency roll-off is especially improved by ∼15% over reference device. The emission spectra almost do not change with the changing drive voltage; that is, Commission Internationale de I’Eclairage coordinates x and y vary only ±0.002 and ±0.008 from 8 to 14 V. The improvement of electroluminescence performances is attributed to the balanced electron-hole injection and transport, confinement of carriers and excitions within potential...