| Organic semiconductor lasing diodes(OSLs)have the potential applications on the integrated optics and information technology because of flexibility,low-cost,solution processing,et al.It has become the next challenge in the organic optoelectronic fields after the big success of Organic light-emitting diodes(OLEDs).However,the high lasing threshold and low carrier mobility of organic lasing dyes hinder the realization of OSLs.In this paper,a kind of thermal activated delayed fluorescence material(TADF)was used to reduce the threshold of amplified spontaneous emission of BUBD-1,which is a sky blue organic lasing dye,and enhance the external quantum efficiency of BUBD-1 based OLED.The main contents of this paper are as follows:1.The optically pumped amplified spontaneous emission(ASE)characteristics of a sky-blue fluorescent material(BUBD-1)blending with the thermally activated delayed fluorescence molecule DMAC-DPS and the commonly used host molecule CBP was demonstrated in this paper.The photoluminescence quantum efficiency(PLQE)is found to be more than 80%in both of blend films with an optimal concentration.The blending films exhibit the lowest ASE threshold of 1.51?J/pulse(CBP:2wt%BUBD-1)and 1.19?J/pulse(DMAC-DPS:2wt%BUBD-1),which are reduced by 84.7%and 87.1%,respectively,compared with that of BUBD-1 neat film.The transient photoluminescence decay curves with varying temperature indicate that the up-conversion through reverse intersystem crossing(RISC)happens in the DMAC-DPS:2 wt%BUBD-1 blend films.The reduction of ASE threshold in the DMAC-DPS doped blend films may be ascribed to a higher energy transfer efficiency caused by both prompt and delayed F?rster energy transfer.This study shows that TADF materials have great potential in reducing the ASE threshold of organic laser materials.2.The OLEDs were fabricated with a hybrid film as the light emitting layer,which includes the TADF host matrix and the sky-blue fluorescent material guest.The optoelectronic properties of OLEDs were enhanced by adjusting the device structures properly.The basic structure is ITO/NPB(40 nm)/DMAC-DPS:x%BUBD-1(40nm)/Bphen(30 nm)/Li F(0.5 nm)/Al.The external quantum efficiency(EQE)of 4.92%was acquired at the optimal doping ratio(2%),which approaches the theoretical EQE limit of the fluorescent OLEDs.We evaporated DMAC-DPS(10nm)between the hole transport layer and the mixed emission layer to improve the utilization rate of the host material,lead to a higher EQE of 5.37%,which breaks the limit of 5%of the EQE of traditional fluorescent OLEDs.Moreover,we evaporated an organic material HAT-CN as the hole injection layer between the anode and the hole transport layer.The formed HAT-CN/NPB heterojunction units effectively reduced the driving voltage of OLEDs.The maximum EQE increased to 5.76%at the same time.In addition,the hole only devices with or without HAT-CN were fabricated.From the Log J-Log V curves and the impedance spectrum analysis,the hole-only devices with HAT-CN improved the hole mobility and reduced the impedance of the devices.This study shows that TADF materials have great potential in enhancing the optoelectronic performance of OLEDs.3.Due to the adopting host-guest system,the lasing properties of BUBD-1 film and the external quantum efficiency of BUBD-1 based OLED were improved.A series of photophysical analysis were done and the results showed that the concerntration quenching was greatly suppressed by the host-guest system,which is the most important issue for improving the properties of BUBD-1 film.At the same time,the enlarged Stokes shift and the radiation decay rate(k_r)are benefit for the population inversion as well as the realization of the amplified spontaneous emission.According to the dipole approximation of electromagnetic radiation,the variation of dipole orientation in pure and composite films,which is measured through the second harmonic generation technique,are in consistent with the the variation of ASE threshold and the EQE of OLEDs. |
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