Highly efficient all solution-processed non-doped deep-blue electroluminescent devices from oligocarbazole-end-capped spirobifluorenes

Abstract

A series of non-doped solution-processed deep-blue emitters namely, 2,7-CSBF, 5,9-CSBF, 2,7-CSF, 2,7-CSFX and 3,6-CSFX, were designed and synthesized by attaching the structurally hindered electron-donating oligocarbazole unit to various deep-blue fluorescent spirobifluorenes. 2,7-CSBF, 5,9-CSBF, 2,7-CSF and 2,7-CSFX having the oligocarbazole unit electronically conjugated link with their backbones showed strong deep-blue emission in the film state with good hole-transporting ability, high quality amorphous film forming capability via spin-coating process and thermal and electrochemical stable assets. As non-doped emissive layers, their double-layer all solution-processed OLEDs emitted a deep-blue color. The devices yielded excellent electroluminescence (EL) performance with low turn-on voltages (V_on) and high maximum external quantum efficiencies (EQE) in the range of 2.8–3.4 V and 1.71–4.10%, respectively. Notably, 5,9-CSBF, owing solid-state fluorescence quantum yield as high as 85% and hole mobility of 1.30 × 10⁻⁷ cm² V⁻¹ s⁻¹, delivered a brilliant EL performance of all solution-processed non-doped deep-blue OLED with CIE coordinates of (0.150, 0.091), V_on of 3.4 V, EQE of 4.10% and luminance efficiency of 4.42 cd A⁻¹, which is one of the best among all-solution-processed deep-blue OLEDs reported to date.