Bright and efficient inverted organic light-emitting diodes with improved solution-processed electron-transport interlayers

Highly efficient inverted organic light-emitting diodes (iOLEDs) are reported by including in the structure a surface modifier, polyethylenimine-ethoxylated (PEIE), to decrease the cathode work function and a hole blocking layer, 1,3,5-tris(N-phenylbenzimidazol-2-yl) benzene (TPBi) to increase the efficiency of the device. The two compounds have been processed in a single step, by using a mixture PEIE: TPBi spun from the same solution. It is demonstrated by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) that a bilayer is formed and same performances as the separately processed materials are obtained. This technic enables to reach high luminances (40 000 cd m(-2)) and high current efficiencies (13 cd/A) using the conjugated Super Yellow (SY) polymer as the emissive layer while reducing the number of processing steps. (C) 2017 Elsevier B.V. All rights reserved.