Dual electroluminescence of an amino substituted 1,3,5-triphenylbenzene

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Abstract
The electroluminescent properties of 5 ′ -[ 4-[bis(4-ethylphenyl)amino]phenyl ] -N,N,N ′ ,N ′ - tetrakis(4-ethylphenyl) -[1,1 ′ :3 ′ ,1 ″ -terphenyl]-4,4 ″ -diamine (pEFTP) were investigated in a vapor deposited layer and dispersed in a polymer matrix. Blue–violet electroluminescence was observed, after applying voltages beyond 12 V for the single layer devices and 22 V for the double layer devices. The electroluminescence(EL) spectrum shows two maxima, of which one corresponds to that of the photoluminescence spectrum. Either direct radiative recombination of the hole and the electron residing at two neighboring molecules or phosphorescence is causing this red shifted electroluminescence maximum. Transient electroluminescence measurements allow us to estimate the mobilities of the charge carriers in the different transport layers. The occurrence of an EL overshoot after switching off a voltage pulse, confirms the importance of detrapping and interfacial phenomena in the radiative recombination in pEFTP.