Efficient Solution-Processable Non-Doped Emissive Materials Based on Oligocarbazole End-Capped Molecules for Simple Structured Red, Green, Blue, and White Electroluminescent Devices

Three primary color-emissive oligocarbazole end-capped molecules (namely, CSBF, CPhC, and CNTD) were designed and synthesized by end-capping different aromatic fluorophores of naphtho­[2,3-c]­[1,2,5]­thiadiazole, phenanthrocarbazole (PhC), and spiro­[benzo­[c]­fluorene-7,9′-fluorene] with a structurally hindered electron-donating oligocarbazole unit. CSBF, CPhC, and CNTD exhibited strong pure blue, green, and red fluorescence emission colors in solid films, respectively, with hole-transporting property, high thermal and electrochemical stability, and excellent film-forming property by a solution casting process. The ternary blend thin film of CSBF/CPhC/CNTD (97.3:1.7:1.0) showed a high-quality mixed and compatible thin film with a high photoluminescence quantum yield of 84%, pure white color emission, and a good hole mobility of 9.75 × 10–8 cm2 V–1 s–1. The solution-processed organic light-emitting diodes (OLEDs) using these materials as a non-doped emissive layer produced deep blue, green, saturated red, and white emission colors with CIE coordinates of (0.15, 0.09), (0.31, 0.58), (0.67, 0.33), and (0.33, 0.32), which are about the points for standard pure deep blue, green, red, and white colors. These OLEDs delivered low turn-on voltages (V on) of 3.0–4.6 V, high luminance efficiencies (LEs) of 1.25–6.67 cd A–1, and high maximum external quantum efficiencies (EQEs) of 1.74–4.10%. In particular, the white OLED showed a remarkable device performance with a V on of 3.0 V, an EQE of 4.02%, an LE of 6.67 cd A–1, and great white color purity and stability. Our results prove that the oligocarbazole unit is a multipurpose component for constructing solution-processable light-emitting molecules with different emission colors. It not only helps to maintain the high emissive property of the fluorophores but also enhances their hole-transporting property, allowing a simple device architecture to be fabricated with high electroluminescent efficiency.