A molecularly doping method for polymer devices: maskless dye diffusion technique

The molecularly doping is known as an efficient way to improve various properties of polymers. For example, the conversion performance of polymer photocells can be drastically enhanced by incorporation of appropriate molecules. In polymer light-emitting device, the emission color is tunable by doping appropriate dyes into emission layer. However, the molecularly doping by conventional method based on mixing the solutions of polymer and dopant should not be compatible to the patterning of the emission color, which is requisite for full-color display. Here, we show a novel molecularly doping method for polymer devices, the maskless dye diffusion technique. In this method, the highly doped and non-doped polymer films are brought into contact, and the electrode beneath the non-doped polymer film is heated by means of Joule heating. Then, the thermally activated dopant molecules diffuse into the non-doped polymer films. The most important feature of the present method is that the doping region can be limited near the electrode. That is, the doped region directly reflects the shape of electrode. With this technique, three-color (RGB) polymer light-emitting devices have been successfully integrated on a glass substrate. The application of this technique to a color-sensing device is also proposed.