Synthesis Of Benzimidazole Derivatives Electron Transport Materials And Application In OLEDs

In this work,we designed and synthesized two alcohol-soluble electron transport materials（ETMs）with high electron transport mobility,pPBIPO and mBPBIPO,which were characterized by NMR spectra and HRMS technology.Properties of the two ETMs were investigated.Phorophysical and electronchemical properties were investigated by UV-vis spectra,PL spectra,CV curves and phosphorescence spectra,by which we estimated their energy gaps of 3.54 eV and 3.59 eV,LUMO levels of-2.87 eV and-2.82 eV,HOMO levels of-6.41 eV,triplet energy levels of 2.63 eV and2.67 eV,respectively.Electron transport properties were investigated by SCLC method,and electron mobility of pPBIPO and mBPBIPO were estimated as 1.67×10^-4（88）²·(1^-1·^-1 and 2.15×10^-4（88）²·(1^-1·^-1,respectively.DSC curves were measured and the glass transition temperature was estimated as 81°C and 110°C,respectively.Surface properties of spin-coating films were investigated by XRD spectra and AFM images.The RMF values were 2.229 nm and 2.399 nm,respectively.In this work,pPBIPO and mBPBIPO were utilized as electron transport materials in fully solution-processed OLEDs,and green as well as blue PhOLEDs were fabricated by orthogonal solvents process.Green PhOLEDs using PEDOT:PSS as hole injecting materials and PBIPO as electron transport materials were fabricated,which exhibited current efficiency of 25 cd·A^-1 and turn-on voltage of 4.0 V.Using PVK as hole transport materials and PBIPO as electron transport materials,green PhOLEDs with better performance were fabricated.For the device with mBPBIPO as electron transport material,current efficiency of 38.43 cd·A^-1 and turn-on voltage of 2.9 V were obtained.Similar with the green devices research process,a serious of blue devices were fabricated.By device architecture optimization,current efficiency of 4.57 cd·A^-11 was finally obtained for blue PhOLEDs.On the other hand,planar P-N heterojunction deep-blue OLEDs were fabricated using PBIPO as N-type layer and NPB as P-type layer.Turn-on voltages of 2.8 V as well as 3.1 V and current efficiency of 2.32 cd·A^-1 as well as 1.99 cd·A^-11 were achieved,respectively.Comparing with the common exciplex-type device with a binary-mixed film as an emitting layer,the planar p-n heterojunction device exhibited much lower V_onn and much higher device efficiency,providing a new strategy for the development of deep-blue light OLEDs.