Near infrared polymer light-emitting diodes

High efficiency of near infrared polymer light-emitting diodes with bilayer structure was obtained. The diode structure is ITO/PEDOT/LI/L2/Ba/Al, where L1 is phenyl-substituted poly [p-phenylphenylene vinylene] derivative (P-PPV), L2 is 9,9-dioctylfluorene (DOF) and 4,7-bis(3-hexylthiophen)-2-yl-2,1,3-naphthothiadiazole (HDNT) copolymer (PFHDNTI0). The electroluminescence (EL) spectrum of diodes from PFHDNTI0 is at 750 nm located inthe range of near infrared. The maximum external quantum efficiency is up to 2.1% at the current density of 35 mA/m^2. The improvement of the diode's performances was considered to be the irradiative excitons confined in the interface between L1 and L2 layers.