Change of the dominant luminescent mechanism with increasing current density in molecularly doped organic light-emitting devices |
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Authors: | Liang Zhou Qingguo Meng Fengyi Liu Jiangbo Yu Ruiping Deng Zeping Peng Zhefeng Li Zhiyong Guo |
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Institution: | Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, The Chinese Academy of Sciences, Changchun 130022, People's Republic of China |
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Abstract: | We have fabricated and measured a series of electroluminescent devices with the structure of ITO/TPD/Eu(TTA)3phen (x):CBP/BCP/ALQ/LiF/Al, where x is the weight percentage of Eu(TTA)3phen (from 0% to 6%). At very low current density, carrier trapping is the dominant luminescent mechanism and the 4% doped device shows the highest electroluminescence (EL) efficiency among all these devices. With increasing current density, Förster energy transfer participates in EL process. At the current density of 10.0 and 80.0 mA/cm2, 2% and 3% doped devices show the highest EL efficiency, respectively. From analysis of the EL spectra and the EL efficiency-current density characteristics, we found that the EL efficiency is manipulated by Förster energy transfer efficiency at high current density. So we suggest that the dominant luminescent mechanism changes gradually from carrier trapping to Förster energy transfer with increasing current density. Moreover, the conversion of dominant EL mechanism was suspected to be partly responsible for the EL efficiency roll-off because of the lower EL quantum efficiency of Förster energy transfer compared with carrier trapping. |
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Keywords: | Current density Doping concentration Carrier trapping Fö rster energy transfer Efficiency roll-off |
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