Polymer—Metal Interfaces and the P-I-N Structure of the Polymer Light-Emitting Diode

Abstract

Conjugated polymers are often treated as semiconductors with low doping concentrations. The nature of the metal/polymer interface is quite sensitive to the work function of the contact metal. In this manuscript, we present evidence to show that the pinning of the surface Fermi level effect commonly observed at the silicon/metal interface can also be observed at the metal/polymer interface. It is achieved by controlling the doping level at the metal/polymer interface. For the cathode side, the heavily n-doped region pins the surface energy level, hence the polymer interface at the cathode side is no longer sensitive to the work function of the overcoated metal. On the other hand, a p-doped region at the anode side pins the surface energy level and makes the contact insensitive to the work function of the anode. Therefore, an efficient polymer LED with the p-i-n structure has been demonstrated without the matching of the work function of the metal electrodes.