Almost completely dedoped electrochemically deposited luminescent films exhibiting excellent LED performance

An improved method for electrochemical deposition (ED) of a novel precursor (peripheral carbazole substituted 9,9'-spirobifluorene (TCPC)) for fabricating highly efficient luminescent films and devices has been developed. Electrochemical deposition often leaves residual charged ion species within the film. These species can negatively impact the performance of these films in OLED applications. The amount of residual charged species in the films can be reduced by controlling the oxidation and reduction potentials, by using electrolytes with different counter anions, and by washing with solvents. An optimized ED process showed a significant decrease in the doping level; up to 0.07% in ED film. The films prepared under a scan potential range from 0.85 to -0.8 V, using TBAAsF(6) as the supporting electrolyte, and washed with solvent mixtures of acetonitrile and CH2Cl2 (V/V = 2/3) demonstrated excellent device performance. Light-emitting devices fabricated by electrochemical deposition achieved deep blue emission (x, y) = (0.16, 0.06) in CIE coordinates. High luminance efficiencies of 2.3 cdA(-1) were achieved for single-layer device; luminescence efficiencies of 4.4 cdA(-1) were achieved for a double-layer device. Finally, the problem that ED films usually exhibit low electroluminescent efficiency is solved. (C) 2009 Elsevier Ltd. All rights reserved.