Identification of device degradation positions in multi-layered phosphorescent organic light emitting devices using water probes

We exposed regions of green phosphorescent organic light emitting devices (PHOLED ^TMs) consisting of a fac-tris(2-phenylpyridine)iridium (Ir(ppy) ₃) as the phosphorescent emitter to a partial pressure of water of 3 × 10 ^-4 Pa during device fabrication to induce degradation in a specific region of the multi-layered devices. We identified the interface between the hole transport layer and the emissive layer as the most susceptive region to degradation. We discuss the luminance loss mechanism and estimate an operational lifetime of 10 000 h, after 20 loss of the initial luminance from 1000 cd/m ², is attainable from an Ir(ppy) ₃ PHOLED fabricated under ultra-high vacuum conditions.