Can an organic phosphorescent dye act as a charge transporter?

The hole transport property of a widely used phosphorescent dye, tris(2-phenylpyridine) iridium or Ir(ppy)3 was investigated by thin film transistor (TFT) technique. The field effect (FE) mobility of Ir(ppy)3 was found to be 1.7 × 10−5 cm2 V−1s−1. This value is actually comparable to NPB and CBP, two popular hole transporting materials for fluorescent and phosphorescent organic light-emitting diodes (FOLED and POLED), respectively. In addition, temperature dependent measurements were carried out to study the energetic disorder (σ) of Ir(ppy)3. The extracted σ ∼ 88 meV is comparable to those of other common amorphous organic hole transporters, which are in the range of 80–90 meV. Our findings indicate that the dye can directly act as a hole transporting component in POLEDs.