Highly oriented crystalline thin film with high electroluminescence performance fabricated by weak epitaxy growth

Abstract

Efficient control on the growth of organic crystalline films is crucial for developing organic electroluminescent devices. Herein, a highly crystalline thin film of a blue-light-emitting material, 1,2-diphenyl-1H-phenanthro[9,10-d]imidazole (PPI) derivative, 1,4-bis(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)benzene (ρ-DPPI), has been achieved by the weak epitaxy growth (WEG) method. The ρ-DPPI molecules with an edge-on orientation grow epitaxially on the inducing layer, forming the continuous and uniform crystalline thin film. The photoluminescence (PL) spectrum of the ρ-DPPI thin film fabricated by weak epitaxy growth was blue-shifted relative to that of the amorphous ρ-DPPI thin film. Also, its PL quantum yield was measured and found to be 64.5%. The electroluminescence performance was evaluated and a fluorescent OLED that emits deep-blue light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.11) has been achieved. The device exhibits high performance with a maximum current efficiency, power efficiency and external quantum efficiency of 4.5 cd A−1, 4.1 lm W−1 and 4.1% at 200 cd m−2, which demonstrates its potential as a highly efficient emitter. The further adoption of the WEG method would advance the knowledge of the growth behavior of luminescent materials and provide desired properties for their electroluminescent applications.