Color variable multilayer light emitting devices based on conjugated polymers and oligomers

We report the fabrication and study of color variable multilayer light emitting devices based on pyridine-containing conjugated polymers and para-sexiphenyl (6P) oligomer. Polarity controlled two color devices were fabricated by sandwiching the emitting layer in between emeraldine base and sulfonated forms of polyaniline (SPAN). The emitting layer typically is a blend of two polymers, one of which is a pyridine-based copolymer (PPyVPV). The devices can be operated under either polarity of driving voltage with different colors of light being emitted from different locations. Under forward bias, red light is generated from PPyVPV/SPAN interface. Under reverse bias, light is generated from the bulk of the emitting layer whose color is dependent on the materials used. Voltage controlled multicolor devices were fabricated by combining the pyridine-based polymers with the 6P oligomer. Voltage dependent multicolor emission was observed in both bilayer and trilayer devices. The emission colors of single devices cover a wide range of visible spectra whose CIE color coordinates vary from blue to white to green with increasing voltages.