Reasearch On Blue Crystalline Organic Light-emitting Diodes Based On Phenanthroimadazole

Traditional amorphous organic light-emitting diode(A-OLED)has the advantages of self-luminescence,wide viewing angle,fast response,flexible and bendable,high efficiency,energy saving,etc.It is a new generation of full-color display and solid-state lighting technology,which has been successfully applied to smart phones,large-size TVs and other display fields.OLED full-color display and white light illumination require the three primary colors of red,green,and blue.At present,compared with the efficient and stable red and green OLEDs,the efficiency and stability of blue OLEDs have always been the shortcomings in OLED display and lighting.It is the "culprit" that caused the "burn-in" of OLED TVs.Therefore,high-efficiency,high-stability blue OLED is the research focus of the majority of scientific researchers.Compared with traditional organic amorphous materials,organic crystalline materials have regular molecular arrangement,low impurity content,good thermal stability and high carrier mobility,so crystalline organic light-emitting diode(C-OLED)based on organic crystalline materials has potential application value in improving the efficiency and stability of devices.In this paper,we take phenanthrimidazole blue organic materials as the research object to prepare epitaxial crystalline films by weak epitaxial growth technology and study the properties of the crystalline films.Then we fabricate C-OLED based on the crystalline films.The specific work content is as follows:1.Taking the blue light compounds 2FPPICz and 2FPPIPCz,which are synthetised by Professor Wang Yue of Jilin University,as the research object,the thermal properties,electrochemical properties,photophysical properties,carrier transport properties and electroluminescence properties of the two compounds are systematically studied.The study found that the two compounds have good thermal stability and similar energy level structures.The results of the single-carrier devices show that although both compounds can effectively transport holes and electrons,they are more inclined to transport holes.At the same time,under the same driving voltage,2FPPIPCz has a larger current density than 2FPPICz.Non-doped devices based on the two compounds as the light emitting layer both exhibit deep-blue light emission.Among them,the non-doped device based on 2FPPIPCz has a maximum external quantum efficiency of 5.6%,a maximum luminance of 24150 cd m-2,and a CIE color coordinate of(0.150,0.075).In addition,the device also exhibites extremely low efficiency roll-off.2.Taking the blue light compound 2FPPICz as the research object and using the banana-shaped small molecule BP IT as the inducing layer,a large area continuous,high-quality epitaxial crystalline film based on 2FPPICz is prepared by weak epitaxial growth technology.At the same time,the 2FPPICz epitaxial crystalline film exhibits deep-blue emission and its photoluminescence spectrum is similar to that of 2FPPICz in dilute toluene solution with obvious vibrational fine structures,indicating that the interaction between molecules becomes weaker in 2FPPICz epitaxial crystalline film,which is different from the strong intermolecular force under disordered accumulation of 2FPPICz amorphous film.More importantly,the hole and electron mobility of 2FPPICz epitaxial crystalline film are as high as 0.1 cm2 V-1 s-1 and 0.015 cm2 V-1 s-1,respectively,which are much higher than other traditional organic amorphous amorphous films(10-8?10-2 cm2 V-1 s-1).3.Taking the 2FPPICz epitaxial crystalline film as the research object,an undoped C-OLED based on the 2FPPICz epitaxial crystalline film is prepared.The non-doped C-OLED exhibits deep-blue emission with a maximum emission wavelength of 405 run and a CIE color coordinate of(0.162 0.029),and its turn-on voltage is only 3.0 V,and the maximum external quantum efficiency is 1.6%.In order to improve the luminous efficiency of C-OLED,a highly efficient doped C-OLED with a host-guest doping ratio of 7:1 is fabricated with the 2FPPICz epitaxial crystalline film as the host and 2FPPIPCz as the doped guest.The guest molecules of 2FPPIPCz are doped into the 2FPPICz host lattice by way of displacement(substitutional)doping.The turn-on voltage of doped C-OLED is 3.0 V,the maximum luminous brightness and maximum external quantum efficiency are 8007 cd m-2 and 2.7%,respectively,and its CIE color coordinates are(0.158,0.034).More importantly,due to the high carrier mobility of the 2FPPICz crystalline host and the high fluorescence quantum efficiency of the 2FPPIPCz guest,compared to other traditional A-OLEDs with high external quantum efficiency,the doped C-OLED has the lower driving voltage of 4.1 V with the the brightness of 1000 cd m-2.In addition,under the same driving voltage,the doped C-OLED also has the higher photon emission and the lower Joule heat loss ratio.