Identification of Emissive Interface-Related Defects in Polyfluorene-Based Light Emitting Devices

We report on a distinct defect related emission band between 2.45 and 2.6 eV in blue light emitting polyfluorene type polymer light emitting devices. The origin of this novel feature at 2.45–2.6 eV which becomes apparent in addition to the well investigated emission band from bulk keto defects at 2.3 eV is spatially located close to the cathode of the device. It is identified as being related to chemical defects in the polymer, formed by a chemical reaction of the polymer in the presence of the deposited cathode metals Al or Ca.