High brightness phosphorescent organic light emitting diodes on transparent and flexible cellulose films

Organic light-emitting diodes (OLED) were fabricated on flexible and transparent reconstituted cellulose obtained from wood pulp. Cellulose is naturally available, abundant, and biodegradable and offers a unique substrate alternative for the fabrication of flexible OLEDs. Transparent cellulose material was formed by dissolution of cellulose in an organic solvent (dimethyl acetamide) at elevated temperature (165 degrees C) in the presence of a salt (LiCl). The optical transmission of 40-mu m thick transparent cellulose sheet averaged 85% over the visible spectrum. High brightness and high efficiency thin film OLEDs were fabricated on transparent cellulose films using phosphorescent Ir(ppy)(3) as the emitter material. The OLEDs achieved current and luminous emission efficiencies as high as 47 cd A(-1) and 20 lm W-1, respectively, and a maximum brightness of 10 000 cd m(-2).