Electrical and optical properties of an alcohol soluble aminoalkyl-substituted cationic conjugated polymer

The optical and electrical properties of a novel alcohol soluble aminoalkyl-substituted cationic conjugated polymer, poly[9,90-bis(600-(N,N,N-trimethylammonium)-hexyl) fluorene-co-alt-2,5-dimethoxy-1,4-phenylene dibromide] (PFPB), has been studied using absorption, photoluminescence, current–voltage–luminescence (J–V–L), and noise characterization techniques. The absorption and photoluminescence studies show that PFPB is blue-emitting, and its long alkyl side chains and two methoxy side chains introduce steric hindrance in the structure, which can minimize interchain interactions. The photoluminescence quantum efficiency of PFPB in methanol was found to be 69.6%. Polymer light emitting diodes (PLEDs) were fabricated using PFPB as an electron injection layer and device physics has been studied. The obtained device results indicate that PFPB can be used as an electron transport layer (ETL) to improve the PLED performance. The noise characteristics on the PLED devices show that the interface between the cathode and the emissive layer is improved through the introduction of a PFPB layer. Results in this report indicate that the poly(fluorene-co-phenylene)- based water/alcohol soluble cationic conjugated polymer avoids the intermixing between the electroluminance layer and adjacent ETL layer which is a common and serious problem in multilayer PLED fabrication by solution casting methods. This makes water solubility materials attractive for applications in PLEDs and other organic devices.