Effect of adjusting charge transport on optoelectronic performances of polymer light-emitting diodes based on SY-PPV

Unconjugated polymer poly(vinylcarbazole) (PVK) was incorporated into poly[{2,5-di(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene}-co-{3-(4′-(3″,7″-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene}-co-{3-(3′-(3′,7′-dimethyloctyloxy) phenyl)-1,4-phenylenevinylene}](SY-PPV) as the emissive layer of PLEDs. The unconjugated backbone of PVK effectively restrains the hole transport property of SY-PPV, which is advantaged to realize better charge-transport balance. Subsequently, the blue-lighting polymer poly[(9,9-dioctyl-2,7-fluorene)-co-(dibenzothiophene -S,S-dioxide)](SO10), which has a deep highest occupied molecular orbital, was employed as the hole-blocking layer to further balance the charge transportation of the emissive device. The SO10 can effectively restrict the hole carrier entering into cathode interface, which is instrumental in avoiding exction quenching on the cathode interface. Through optimizing device structure, a maximum luminous efficiency of 13.52 cd A⁻¹ was realized, which is achieved 120% improvement of that of the pristine SY-PPV as emissive layer. These results indicate that incorporating unconjugated polymer and hole-blocking layer is an efficient method to adjust charge-transport balance of hole-type emissive materials.