We report on the optimization of organic light emitting diode (OLED) devices using 1,8-di-(4-trifluromethylphenyl)-anthracene (CF3-DPA) as the active emissive layer. CF3-DPA emits in the deep blue region with an emission peak at 432 nm in solution which showed a slight red shift in thin films. CF3-DPA hashigh reported fluorescence quantum efficiency,~67%, as compared to 9,10-diphenyl anthracene (9,10-DPA).We optimized the OLED devices with different hole transporting layers (HTLs). Bilayer devices formed with N,N' -di(1-naphthyl)-N,N' -diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD) as the HTL gave a reasonable light output. We observed that trilayer or multilayer devices with the inclusion of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and/or copper phthalocyanine as an additional HTL reduced the turn on voltage by ~5 to 9 V, though the brightness of the light emission also decreased. Including suitable carrier (electron or hole) transporting layers like 2, 2' ,2''' -(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)and 4,4' -Bis(N-carbazolyl)-1,1' -biphenyl (CBP) increases the efficiency of the devices. From our studies, we conclude that though NPD/CF3-DPA interface is crucial for light emission, the performance of the devices is limited by the mismatch of the hole and electron mobilities and the low internal quantum efficiency of CF3-DPA in the solid state. Devices having ITO/NPD/CF3-DPA/TPBi/LiF-Al geometry were observed to be the most efficient.
Volume 134, 2022
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