Preparation Of Triarylamine-based Electron-blocking Materials And Their Device Performance

With the widespread use of OLED devices,people have increasingly high requirements for the efficiency and lifetime of OLED devices,but there has been no breakthrough in high-efficiency and long-life blue OLED devices,so it is more urgent to improve the efficiency and lifetime of blue OLED devices.For the currently used blue fluorescent OLED devices based on the trilinear state-trilinear state annihilation(TTA)mechanism,the electron blocking layer plays a role in enhancing the utilization of trilinear state excitons and blocking electron leakage,which can improve the efficiency and lifetime of the devices.Based on this,four triarylamine-based electron-blocking materials were designed and synthesized in this thesis to investigate the effects of different electron-blocking materials and different electron-blocking layer thicknesses on device efficiency and lifetime,with the main research content as follows:The four triarylamine-based electron-blocking materials EB1,EB2,EB3 and EB4 were designed using triarylamine as the backbone and N-phenylcarbazole,dibenzofuran and 2,3-benzocarbazole as the main modifying groups.The structures of the intermediates and the target compounds were characterised by NMR hydrogen spectroscopy,carbon spectroscopy and mass spectrometry,indicating the successful synthesis of the target compounds.Quantum chemical calculations show that EB1-EB4 have suitable highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)energy levels,matching the energy levels of the chosen hole transport and luminescent layer materials.The results of the differential scanning calorimetry and thermal weight loss tests show that EB1-EB4 have a glass transition temperature(T_g)greater than 120°C and a thermal decomposition temperature(T_d)around 500°C,both of which have high thermal stability.The results of photoluminescence spectroscopy show that EB1-EB4 have a maximum emission peak between407 nm and 435 nm,which is a blue-violet emission;the results of low temperature phosphorescence spectroscopy show that EB2 compounds have the highest trilinear energy level of 2.68 e V;the results of multi-turn cyclic voltammetry show that EB1-EB4 have good electrochemical stability.Twelve blue fluorescent OLED devices with electron-blocking layer thicknesses of 5 nm,10 nm and 20 nm were prepared using EB1-EB4 as electron-blocking layer materials to investigate the brightness-voltage performance,efficiency-current density performance and lifetime performance.The comparative analysis of the four EB2 materials with the same barrier thickness shows that the EB2-based devices have the best performance with a brightness start voltage of 2.62 V,maximum Index efficiency,power efficiency and external quantum efficiency of 248.53,11.43 lm/W and 23.61%respectively,and a maximum LT95 lifetime of42.30 h.The comparative analysis of the devices with different barrier thicknesses shows that the EB2-based devices have the best performance with a brightness start voltage of 2.62 V,maximum Index efficiency,power efficiency and external quantum efficiency of 248.53,11.43lm/W and 23.61%respectively.A comparative analysis of the devices with different barrier thicknesses shows that the EB2-based devices with a barrier thickness of 10 nm have the best overall performance compared to the 5 nm and 20 nm devices,with a 7.54%and 11.82%increase in lifetime and only a 2.68%and 1.76%decrease in efficiency,respectively.