| In this dissertation,the long-range coupling mechanism of electron-hole pairs was investigated in an interfacial exciplex OLED device with a structure of ITO/MoO3(5 nm)/CBP(40 nm)/3DTAPBP(10 nm)/PO-T2T(50 nm)/LiF(0.6nm)/Al(130 nm).In order to explore the effects of spacer layers on electroluminescence(EL)properties of the devices,three types of spacer materials with different thicknesses were inserted at the interface between the exciplex donor 3DTAPBP and the acceptor PO-T2T:(1)DPEPO and TmPyPB;(2)26DCzPPy;(3)mCP and PYD-2Cz.For spacer materials DPEPO and TmPyPB,the maximum distances of the long-range coupling of electron-hole pairs were only 6 nm and 8 nm,respectively.Corresponding,the blue shift of spectra of 3DTAPBP/PO-T2T exciplex were only 18 nm and 19 nm.The suggestion is that they possess excessively deep HOMO levels,low hole/electron mobility and inability of forming exciplexes with donor 3DTAPBP or acceptor PO-T2T.For the spacer material 26DCzPPy,due to its good carrier mobility and the characteristic of forming exciplex not only with the donor 3DTAPBP,but also with the acceptor PO-T2T,the maximum distance of the long-range coupling of electron-hole pairs of this exciplex was extended to 18 nm,and the EL spectrum had a blue shift of 39 nm while basically maintaining the same shape.The addition of spacer layer also increased the maximum EQE of the device from 3.45%to 4.64%,which was improved by 34.5%.The spacer materials mCP and PYD-2Cz,which have similar molecular structures,are hole transport material and bipolar material,respectively.Both of them can only form exciplex with the acceptor PO-T2T.These characteristics further extended the maximum distance of the long-range coupling of electron-hole pairs of this exciplex to 30 nm and 50 nm,respectively,and the EL spectrum had a blue shift of 35 nm and 41 nm,respectively,while basically maintaining the same shape.The addition of spacer materials also increased the maximum EQE of the device from 2.73%and 3.38%to 4.91%and 6.64%,respectively,which were improved by 79.9%and 96.4%,respectively.In addition,we have prepared devices with a mCP-doped emissive layer(3DTAPBP:mCP:PO-T2T).Compared with the interfacial structure of 3DTAPBP/mCP/PO-T2T,the doped structure obtained higher EQE(6.57%)and lower efficiency roll-off.Due to the excellent characteristics of PYD-2Cz as a spacer material,the effect on the performance of the TAPC/PO-T2T exciplex was also studied,and the maximum distance of the long-range coupling of electron-hole pairs of 40 nm was obtained.The results showed that the addition of spacer materials can cause a blue shift in the EL spectra of exciplex devices.The spacer forming exciplex with donor or acceptor was favorable for extending long-range coupling of electron-hole pairs and achieving high efficiency.Spacer materials are critical to the distance of the long-range coupling of electronhole pairs and the efficiency of devices.This study provides a reference for the selection of spacer materials and a strategy of achieving blue or even deep-blue exciplex emission. |
