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13 September 2012 Inverted OLEDs for flexible displays
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We reported a couple of methods to improve electron injection from the ITO electrode, thereby to fabricate efficient inverted bottom emission organic light emitting diodes (IBOLEDs). The first method is to use an n-doped electron transporting layer (ETL) as the electron injection layer. Electron only device characteristics and UPS measurements confirmed that B3PYMPM homo-junction has the lowest injection barrier at the interface among three different ETLs, resulting in the highest maximum EQE of 19.8% at low voltage in IBOLEDs. The energy barrier between n-ETL and ETL is one of the most important factors for high performance inverted OLEDs. The second method is to use an organic p-n junction as an electron injection layer, where the p-n junction generated electrons and holes under reverse bias, which corresponds to the forward bias in the OLEDs. The organic p-n junction composed of a p-CuPc/n-Bphen layer shows almost the same electron injection characteristics for the cathodes with different work functions whereas the injection characteristics of the n-Bphen EIL significantly depend on the work function of the cathode. These facts indicate that the organic p-n junction can be efficiently applied as an electron injection layer for high performance flexible organic electronics, regardless of the electrodes.
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Jang-Joo Kim, Jeong-Hwan Lee, Ji Whan Kim, Sei-Yong Kim, Seung-Jun Yoo, Po-Sheng Wang, and Chih-I Wu "Inverted OLEDs for flexible displays", Proc. SPIE 8476, Organic Light Emitting Materials and Devices XVI, 84760G (13 September 2012);

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