Improvement of the electrical characteristics of polymer electroluminescent structures by using spray-coating technology

In this article, polyphenylenevinylene derivative (poly(9,9-dihexyl-9H-fluorene-2,7-diyl-vinylene)) (PPV-D) thin films were deposited by spray deposition and spin-coating. Film morphology was investigated by scanning electron microscopy images and surface profile diagrams. The traps concentration depending on the deposition method was evaluated based on current-voltage characteristics of ITO/PPV-D/Al structures measured at different temperatures. Brightness-voltage characteristics of the structures containing spray deposited and spin-coated PPV-D films with the same thickness were measured. The film surface at spray deposition tends to be uniform and smoother than the spin-coated one. The structure with sprayed polymer layer showed higher maximal trap factor (0.94 x 10(-3) vs 0.83 x 10(-3) for spin-coating), which is evidence for less defects in the bulk and presence of more free carriers, contributing to the conduction and the radiative recombination. Twice-higher luminance and 1.4 V lower turn-on voltage were achieved, using spray deposition in comparison with the spin-coating technique. The spray technique for polymer deposition is a very powerful tool for the preparation of cost effective organic-based devices with improved electrical characteristics and efficiency.