Copper hexadecafluorophthalocyanine and copper phthalocyanine as a pure organic connecting unit in blue tandem organic light-emitting devices

Abstract

A nondoped organic system of copper hexadecafluorophthalocyanine $\left({\mathrm{F}}_{16}\mathrm{Cu}\mathrm{Pc}\right)∕\text{copper}$ phthalocyanine (CuPc) has been investigated as a connecting unit for deep-blue electrofluorescent tandem organic light-emitting devices (OLEDs) based on 2-methyl-9,10-di(2-naphthyl) anthracene emission. Such devices exhibited a doubling in current efficiency from $0.63\text{to}1.47\mathrm{cd}∕\mathrm{A}$ at $J=100\mathrm{mA}∕{\mathrm{cm}}^2$ as compared to the single-unit device. The pure organic connecting unit showed superior optical transparency $(\sim 100\%)$ , resulting in minimal microcavity effect in the devices. Interface dipole and band bending on both sides of the ${\mathrm{F}}_{16}\mathrm{Cu}\mathrm{Pc}∕\mathrm{Cu}\mathrm{Pc}$ interface suggested the formation of an intrinsic $p\text{-}n$ junction, which is a prerequisite of an effective connecting unit leading to a dramatic performance improvement in the tandem OLEDs.