Synthesis and characterization of greenish-blue light emitting lithium-boron complex for organic light emitting diode applications

Abstract

A lithium-boron complex, lithium tetra (2-methyl 8-hydroxy quinolinato) boron (LiBqm₄), which emits greenish-blue light has been synthesized by the reaction of LiBH₄ with 2-methyl 8-hydroxyquinoline in a molecular weight ratio of 1:4, and used for organic light emitting diodes (OLEDs) fabrication. The complex has been characterized by optical absorption, Fourier Transform Infrared (FTIR), photoluminescence (PL) and electroluminescence (EL) spectroscopic methods. The thermo-gravimetric analysis (TGA) suggests that the material is quite thermally stable up to 380^oC. An optical band gap of 3.15 eV using the well-known Tauc relation and an exciton binding energy of 0.69 eV has been evaluated. OLEDs have been fabricated in ITO/<i style="">N</i>,<i style="">N</i>′-di-(3-methyl-phenyl)-<i style="">N</i>,<i style="">N′</i>diphenyl-4,4′diaminobiphenyl(TPD)/LiBqm₄/Al configuration. PL and EL peaks exist at 503 nm. <i style="">I</i>-<i style="">V</i> characteristic of device reveals that at higher voltages the current follows <i style="">I </i>⍺ <i style="">V</i>^m law, where <i style="">m</i> > 1.