Interface and its engineering are critical to achieve efficient organic light-emitting diodes (OLEDs). In this presentation,
we would like to present a new type of electron transport layer (ETL) based on metal oxide between emissive layer and
metal electrode. The metal oxide synthesized by sol-gel process and can be solution processed on top of the emissive
layer. The efficiency of OLEDs based on green polyfluorene polymer has found increased significantly, from 15
lumen/watt to 19 lumen/watt compared with our previous cathode structure of Cs<sub>2</sub>CO<sub>3</sub>/Al. The electrochemical
properties and electronic structure of the ETL, and energy alignment at the interface are examined to understand the
function of this ETL and the contribution to the improvements for device performances. We will present the details of
the analysis and the composition of the materials in the presentation.