Ultrahigh efficiency green polymer light-emitting diodes by nanoscale interface modification

Qianfei Xu, A.; Jianyong Ouyang, A.; Yang Yang; Ito, Takayuki; Kido, Junji
December 2003
Applied Physics Letters;12/8/2003, Vol. 83 Issue 23, p4695
Academic Journal
We report highly efficient green polymer light-emitting diodes (PLEDs) achieved by introducing a nanoscale interfacial layer, made of calcium (2) acetylacetonate [Ca(acac)[sub 2]], between the aluminum cathode and the green polyfluorene polymer. Ca(acac)[sub 2] is solution processible, therefore it is ideal for the fabrication of PLEDs. It is believed that the Ca(acac)[sub 2] layer plays multiple roles in enhancing the device performance. Firstly, it enhances the injection of electrons, which are the minority carriers in our green polyfluorene PLEDs. Secondly, it provides a buffer layer, preventing the quenching of luminescence from the aluminum electrode. Thirdly, it behaves as a hole-blocking layer, and subsequently enhances exciton formation. Based on Ca(acac)[sub 2]/aluminum cathode, we obtained device efficiency as high as 28 cd/A at 2650 cd/m2 brightness, which is an improvement by a more than a factor of 3 over devices using calcium/aluminum as the cathode. © 2003 American Institute of Physics.


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