ELECTRICAL PROPERTIES OF Au/POLYMER INTERFACES

摘要

A trap-free Molecularly Doped hole-transport Polymer (MDP) provides a model system for the study of metal/polymer interfaces by enabling the use of a recently developed technique that supplies a quantitative measure of contact injection efficiency. The technique combines field-dependent injection current measurements from a contact under test with time-of-flighl (TOF) mobility measurements on the same sample. In the present case, MDP films were prepared with two top vapor-deposited contacts, one of Au (test contact) and one of Al (for TOF), and a bottom carbon-loaded polyimidc electrode. An unusual phenomenon is investigated whereby injection from Au is initially blocking, evolving to ohmic over time. This contrasts with the behavior expected according to the relative workfunctions of Au and of the polymer whereby Au should inject holes efficiently. The samples were aged al various temperatures below the glass transition of the polymer (85℃) and the evolution of current-field measurements and of capacitance is followed in detail over time and analyzed. All Au contacts eventually achieved ohmic injection. Rapid sequence data acquisition enabled the separation of two main processes in the injection evolution. Control measurements ensure that the evolution of the electrical properties is due to the Au/polymer interface behavior and not the bulk. The behavior of Au contacts evaporated under various deposition conditions was compared. Transmission electron microscopy results at the Au/MDP interface were obtained as both a function of time and of deposition conditions. Mechanisms operating at the interface of the evaporated Au films on the polymer are discussed.