Design And Synthesis Of Organic Photoelectronic Materials Based On Spirofluorenexanthene And Their Applications In OLEDs

Organic light-emitting diodes(OLEDs)have become a household name,more and more products based on OLED technology such as smart phones,large-screen TVs,and lighting have entered the homes of ordinary people.Nevertheless,it is still important to continuously improve the efficiency and lifetime of OLEDs.Hole transport materials(HTMs)play an important role in transporting holes to maintain the carrier balance of OLEDs.Developing novel HTMs with green synthetic routes,good thermal stability,suitable energy levels,and high hole mobility will help realize various high-performance and low-cost OLEDs.One of the serious problems in OLED technology is the low efficiency and lifespan of deep blue devices.It is urgent to develop emissive materials that can be used in deep blue OLEDs,but how to balance deep blue emission and high efficiency has always been big trouble for researchers.In this thesis,spirofluorenexanthene(SFX),a classic core for organic semiconductors,has been selected for developing new kinds of HTMs and deep blue emissive materials.Based on the SFX core,different substituent groups have been introduced to the molecules to achieve the corresponding requirements.The entire process from organic material synthesis,materials characterization to device fabrication and testing has been fully completed.The research works in detail are as follows:1.Two small-molecule HTMs DPNA-SFX and DOPNA-SFX based on SFX core and phenylnaphthylamine were designed and synthesized.Their thermal,photophysical,and electrochemical properties have been systematically analyzed.Both materials have excellent thermal stability due to the spiro ring structure.The hole mobility of DPNA-SFX and DOPNA-SFX was studied by fabricating single-carrier devices,both of which were greater than the commercial material NPB.Two HTMs have been successfully used in RGB phosphorescent OLED,and the performance of devices based on them is better than those based on NPB.Among them,the DPNA-SFX based green device has a maximum current efficiency(CE_max)of 89.8 cd A^-1,maximum power efficiency(PE_max)of 94.2 lm W^-1,and maximum external quantum efficiency(EQE_max)of 24.7%.The efficiency roll-off is only2.0%when the brightness is 1000 cd m^-2.The performance of the red device is even better with the CE_maxis 41.1 cd A^-1,the PE_maxis 46.4 lm W^-1,and the EQE_maxis 34.7%.The EQE can still be maintained at 33.3%when the brightness is 1000 cd m^-2with an efficiency roll-off of only 4.0%.Considering the position and purity of the emissive peak,this is the highest efficiency value for red phosphorescent devices using iridium complexes as luminescent materials to achieve pure red luminescence.2.Two small-molecule blue emissive materials SFX-DBF and SFX-DBT based on SFX core and dibenzofuran/dibenzothiophene were designed and synthesized.Similarly,their thermal,photophysical,and electrochemical properties were analyzed.Both materials have wide band gaps,high triplet energy levels,and deep blue emission properties and they have similar absorption and emission spectral curves.Non-doped,doped,and TADF-sensitized devices based on SFX-DBF,SFX-DBT,and commercial fluorescent materials have been prepared and their performance has been comprehensively studied.The results show that non-doped devices based on SFX-DBF and SFX-DBT can successfully achieve deep blue emission,with the CIE coordinates of(0.16,0.03)and(0.16,0.04),respectively.The doped device using DPEPO as the host can improve the efficiency while maintaining deep blue emission.The efficiency of the doped devices using LBH001 as the host can be also improved,but the corresponding emission peaks are red-shifted.After switching to DMAc-DPS as TADF host,the efficiency of devices based on SFX-DBF and SFX-DBT remains basically unchanged,but the emission peak is further red-shifted.In the TADF-sensitized devices with DPEPO as the host and DMAc-DPS as the sensitizer,the performance has been greatly improved.Among them,the CE_max,PE_max,and EQE_maxof the device based on LBD001 are 32.15 cd A^-1,33.67 lm W^-1,and 20.77%,respectively.which is close to the device performance of TADF doped device,but only realizes ordinary blue emission,corresponding to CIE coordinates(0.16,0.20).