The use of ionic salt dyes as amorphous, thermally stable emitting layers in organic light-emitting diodes

The conversion of two neutral dye molecules (D) to ionic salts (H2N-D-NH2. 2HX) and their utilization as emitting layers in organic light-emitting dio des (OLEDs) is described. The dye salts, AEQT . 2HCl and APT . 2HCl, can be deposited as amorphous films using conventional evaporation techniques. X- ray diffraction and scanning electron microscopy analysis, coupled with the rmal annealing studies, demonstrate the resistance of the films to crystall ization. This stability is attributed to strong ionic forces between the re latively rigid molecules. OLEDs incorporating such salts for emitting layer s exhibit better thermal stability compared with devices made from the corr esponding neutral dyes (H2N-D-NH2). These results suggest that ionic salts may more generally enable the formation of thermally stable, amorphous emit ting, and charge transporting layers. (C) 2000 American Institute of Physic s. [S0003-6951(00)01701-0].