EL mechanism of organic LED alternately deposited with diamine derivative and Alq3

The authors have prepared organic light-emitting diodes (OLEDs) alternately deposited with 5 nm-thick diamine derivative (TPD) and 5 nm-thick aluminum quinoline (Alq3), and studied their electroluminescence (EL) and photoluminescence (PL) properties using the dyedoping method. This method revealed the electron injection dependence on the emitting region, inefficient EL of guest dyes with high PL quantum efficiency and the contribution of the half-region on the anode side of a narrower Alq3 layer. Therefore, the carrier recombination in the TPD layer was concluded to occur in the alternately deposited specimen. As TPD cannot block electron transport perfectly, electron-hole recombinations can occur in the TPD layer and produce excitons of TPD. Their energies will be transferred to Alq3 or guest dye molecules. The authors suggest that the generation of the TPD exciton and the energy transfer from TPD to Alq3 play an important role in the EL mechanism in organic LEDs.