Layered polymer light emitting diode prepared by Evaporative Spray Deposition from Ultradilute Solution (ESDUS) technique at various substrate temperature

The evaporative spray deposition from ultra-dilute solution (ESDUS) technique enables preparing a polymer layered structure. The bi-layer structure consisted of two π-conjugated polymers, where the top layer was deposited from tetrahydrofuran (THF) solution with the ESDUS technique onto the preceding bottom layer composed of the other THF-soluble polymer. It has been reported that the external quantum efficiency (EQE) of the polymer light emitting diode (PLED) having the bi-layer structure is significantly higher than a corresponding single-layer device. In the present study, the polymer bi-layer films are prepared at substrate temperatures of 65°C and 80°C. While the photoluminescence of the bi-layer film prepared at 80°C indicated the separation of the two components in the film, that of the film at 65°C suggested partially mixed structure. The PLED composed of the film at 80°C exhibited significantly better performance than that at 65°C and the PLED composed of the spin-coated mixed film. The mixture structure of the two component films can be controlled simply by the substrate temperature during ESDUS deposition.