Red and near-infrared electroluminescence from organic light-emitting devices based on a soluble substituted metal-free phthalocyanine

Red and near-infrared (NIR) organic light-emitting devices (OLEDs) were fabricated based on Tetra (2-Isopropyl-5-methylphenoxyl) substituted metal-free phthalocyanine (Tetra-H2Pc). The devices were fabricated by vacuum deposition and spin coating methods. The electroluminescence (EL) intensity at about 910 nm in the devices based on Tetra-H2Pc was increased by about 14 times compared with the intensity at about 930 nm in the devices based on unsubstituted metal-free phthalocyanine (H2Pc) in the same device structures. The improvement in the EL intensity was attributed to the large steric hindrance of non-peripheral phenoxyl substituent of Tetra-H2Pc. It was found that the NIR EL spectra of the doped devices exhibited a strong dependence on the concentration of Tetra-H2Pc. The emission at 740 nm was from Tetra-H2Pc monomer, while the emissions around 910 nm and 870 nm were from excimer or higher aggregated species.