Dependance on Metal Electrode of Poly(3-hexylthiophene) EL Device

Poly(3-hexylthiophene) 발광소자의 금속전극 의존성

To investigate the effect of metal electrode in electroluminescent[EL] devices, we fabricated EL devices of ITO/P3HT/Al, ITO/P3HT/LiF/Al and ITO/P3HT/Mg:In structure. In current-voltage-light power characteristics, turn-on voltage of EL devices using LiF insulating layer and Mg:In(2.8V) metal electrode is lower than EL device using Al(4.2V). Besides the external quantum efficiency is improved also. The reason is related to carrier mobility and carrier injection, which would affect the hole-electron balance. In the device with Al electrode, holes injected from indium-tin-oxide[ITO] to poly(3-hexylthiophene)[P3HT] might reach the Al electrode without interacting with injected electrons, because the electron injection efficiency was very low for this electrode. Besides oxidation of the Al electrode is likely due to holes reaching the cathode without meeting injected electrons. Another possible reason for the higher EL efficiency may be the insulating layer playing the role of a tunneling barrier for holes to the Al electrode. In all EL devices, the orange-red light was clearly visible in a dark room. Maximum peak wavelength of EL spectrum emitted at 640nm in accordance with photon energy 1.9eV