Pyrene-functionalized carbazole derivatives as non-doped blue emitters for highly efficient blue organic light-emitting diodes

Abstract

A series of pyrene-functionalized carbazole derivatives, namely N-dodecyl-3,6-di(pyren-1-yl)carbazole (CP2), N-dodecyl-1,3,6-tri(pyren-1-yl)carbazole (CP3) and N-dodecyl-1,3,6,8-tetra(pyren-1-yl)carbazole (CP4), are synthesized and characterized as simple non-doped solution processed blue emitters for OLEDs. By multiple substitution of pyrene on the carbazole ring, we are able to retain the high blue emissive ability of pyrene in the solid as well as improve the amorphous stability and solubility of the material. These materials show high solution fluorescence quantum efficiencies (up to 94%) and can form morphologically stable amorphous thin films with Tg as high as 170 °C. Solution processed double-layer OLEDs using these materials as non-doped blue emitters exhibit good device performance with luminance efficiencies up to 2.53 cd A−1. Their multi-layer devices exhibit outstanding performances. The CP2-based device shows a low turn-on voltage (down to 2.6 V) with an excellent blue emission color (λem = 436 nm) and CIE coordinates of (0.16, 0.14), while the CP3 and CP4-based blue devices also display low turn-on voltages (down to 2.7 V) with high luminance (up to 24479 cd m−2) and luminance efficiencies (up to 6.92 cd A−1).