Effects of additives in polymer thick film-organic light emitting diodes (PTF-OLED)

Abstract

The optimum composition and film thickness determined for a single-layer organic light emitting diodes (120–150 cd/m 2 at 30 mA/cm 2) has been determined in one of our previous publication [Display 21 (2001) 199]. In this following study, a series of additives was included in the original composition for the purposes of color tuning, enhancement of the device efficiency as well as the stability of the polymer thick film-organic light emitting diodes (PTF-OLED). The additives attempted including three dyes (rubrene, perylene and DCM), three sensitizers (naphthalene, anthracene and p-terphenyl), several stabilizers (antioxidant and photo-stabilizer) and a number of organic soluble salts known as phase transfer catalyst. Rubrene was found being able to improve the OLED efficiency by 3-fold and its durability by at least 60 times at a concentration of 5–10 pph (in part per hundred of Alq 3 replaced). The color of the OLED can also be tuned according to the additional dye used. The sensitizer naphtahlene can also improved the efficiency of the OLED by 2-fold while the effect of the other additives was less significant. In addition, the lowering of the turn-on voltage and thus a higher current efficiency resulted by the addition of a charge injection layer (lithium fluoride or calcium fluoride) in between the cathode and the organic layer. The performance of the doped PTF-OLED is within an order of magnitude compared to a heterojunction small molecule-based OLED.