High-current injection and transport on order of kA/cm2 in organic light-emitting diodes having mixed organic/organic heterojunction interfaces

We manufactured multilayer organic light-emitting diodes (OLEDs) with mixed organic/organic heterojunction interfaces composed of alpha-sexithiophene and phenyldipyrenylphosphine oxide carrier-transporting layers. In the mixed-interface OLEDs, we achieved a low driving voltage of 3.6 V at a current flow of 100 mA/cm(2), which was caused by efficient carrier injection at the mixed interfaces. We investigated how much current can flow through these OLEDs with the aim of fabricating electrically pumped organic laser diodes. We found that an OLED of this type with a small active area of 625 mu m(2) on a high-thermal-conductivity sapphire substrate can sustain high current densities of 1.1 kA/cm(2) and emits bright electroluminescence of 7.9 Mcd/m(2) under direct current.