Color-variable electroluminescence from poly(p-phenylene vinylene) derivatives

Photoluminescent and electroluminescent properties of poly(2-methoxy-5-nonyloxy-p-phenylene vinylene) (MN-PPV), one of the soluble poly(p-phenylene vinylene) (PPV) derivatives is synthesized through a dehydrochlorination reaction. The EL peak at 576 nm with a low threshold voltage in the monolayer structure is independent of the bias. When the Alq₃ layer is very thin (≤10 nm) in the bilayer structure of ITO/MN-PPV/Alq₃/Al, the intrinsic emission only from MN-PPV is obtained. When the Alq₃ layer gets thicker (approximately 30 nm), the intrinsic emission from Alq₃ at 520 nm will increase gradually with the bias, while emission from MN-PPV decreases. Based on the energy levels and field-assisted tunneling at the surface, we consider that this color-variable EL is ascribed to the redistribution of the electric field on the devices and field-assisted charge crossing through the triangular energy barrier at high biases.