Solution-processed PhOLEDs Based On Mixed Host System And Their Transient Electroluminescence

Organic electroluminescence technology has become a hot spot in the research field because OLED can replace LCD display as a new generation of mainstream display in the field of flat panel display.Solution-processed based inkjet printing technology is the basis for promoting OLED industrialization.In this paper,the phosphorescent organic electroluminescent device is prepared by solution method and optimized reasonably.Especially for the blue phosphorescent OLED which is urgently needed in the academic and industrial circles,the mixed-host system is introduced to prepare high-efficiency and high-quality PhOLED to improve the performance of the device.By comparing the experimental characterization and analysis of mechanism of the light emitting device,the theoretical support to give improved device performance..The main contents are as follows:(1)The blue PhOLED based on different concentrations of blue phosphorescent material FIrpic was prepared by solution processing.It is found that the luminescence of the host material decreases with the increase of doping concentration,that is to say,the energy transfer between the host and the object is complete,and the luminescence of the device is completely derived from the guest material.As the concentration increases,the current density and luminance of the device increase,and the current efficiency decreases when the doping concentration is increased to 15%.This proves that when the doping concentration in the phosphorescent host-guest structure is low,the energy transfer between the host and guest molecules is not complete,which leads to partial host luminescence.When the doping concentration is high,the phosphorescent molecules have triplet-triplet annihilation,which leads to the efficiency roll-off affecting the device.In the second section,we prepared a green PhOLED based on the traditional green phosphorescent material Ir(ppy)3 and the new green phosphorescent material G.The maximum brightness of the Ir(ppy)3 system 24900cd/m2 and the maximum current efficiency 24.4 cd/A was obtained by optimizing the thickness of the luminescent layer.The maximum brightness of the G system is 14600 cd/m2,and the maximum current efficiency is 38.6 cd/A.(2)Comparing the structure of the hole transport layer with the ordinary standard,and introducing the mixed-host structure system into the green phosphorescent OLED and blue phosphorescent OLED prepared by solution processing,and obtaining the PhOLED with improved performance.In the blue phosphorescent device that is currently in urgent need of development,the hybrid body is optimized to obtain PhOLED with a maximum brightness of 7410 cd/m2 and a maximum efficiency of 11.9 cd/A.This proves that the addition of the second material completes the structure of the device,provides an energy level gradient,reduces the energy level barrier,and adjusts the carrier injection to optimize the device efficiency.At the same time,the multi-layer organic layer spin coating similarly added to the hole transport layer in the solution preparation method causes the latter layer to dissolve the former layer to form a mutual solubility phenomenon,and the mixed-host structure not only improves the device but also avoids an additional miscible interface.(3)The mCBP:FIrpic structure PhOLED was prepared and optimized,and the blue phosphorescent organic electroluminescent device was prepared by mCBP and TCTA as the mixed host in solution processing.The study of single carriers found that the addition of TCTA optimizes carrier transport.The transient electroluminescence test shows that the mixed-host device with TCTA has a shorter time to achieve steady-state luminescence than the single-body device,that is,the HOMO level of TCTA provides an energy level gradient,the injection barriers between the HIL and the EML are pulled down.The hole injection is adjusted,and the device reaches steady state luminescence faster.Instantaneous overshoot occurs when the pulse voltage is removed.As the concentration of TCTA increases,the transient overshoot peak decreases first and then increases.Combined with the instantaneous overshoot peak with a slice spectrum of 472 nm characteristic luminescence peak,we can conclude the small spikes are mainly derived from holes(trap level)bound in the guest material and electrons accululated in the host material,which are combined to retreat to emit light after the pulse is turned off.In section 4.3,The maximum current efficiency of the device optimized is 14.49 cd/A at mCBP:TCTA 2:1,and the luminance is still 13.62 cd/A at 1000 cd/m2,which is significantly higher than the single-host PhOLED.The fourth chapter is deeply researched and analyzed by means of transient electroluminescence testing.Based on the microscopic aspects such as hole injection and trapping carriers,it gives an explanation for mixed-host optimization device,and provides theoretical support for the mixed-host system from a new perspective.