Low voltage organic light-emitting devices with triphenylphosphine oxide layer

We have developed low voltage driving organic light-emitting devices using triphenylphosphine oxide $(Ph3PO)$ layers. The devices with a $Ph3PO$ layer show high current density at a low voltage. For example, the current density of $20mA∕cm2$ is achieved at a low voltage of $2.9V$ for the device consisted of $4,4′,4″$-tris[$N$-(2-naphthyl)-$N$-phenyl-amino]-triphenylamine (2-TNATA), $4,4′$-bis(2,$2′$-diphenylvinyl)-$1,1′$-biphenyl (DPVBi), and $Ph3PO$ layers. Due to the good electron conduction property of $Ph3PO$⁠, a luminance of $1017cd∕m2$ is achieved at a low voltage of $3.0V$ in a device with a structure of ITO/2-TNATA/DPVBi:rubrene $(1%,10nm)∕DPVBi$ $(30nm)∕Ph3PO$ $(60nm)∕LiF∕Al$⁠.