Double-Layer Structured WPLEDs Based on Three Primary RGB Luminescent Polymers: Toward High Luminous Efficiency, Color Purity, and Stability

Efficient white polymer light-emitting diodes (WPLEDs) were fabricated on the basis of three kinds of luminescent polymers:  poly{2-[3‘,5‘-bis(2‘ ‘-ethylhexyloxy)benzyloxy]-1,4 phenylenevinylene}-co-poly(2-methoxy-5-(2‘-ethyl-hexy loxy)-1,4-phenylene vinylene) (BE-co-MEH-PPV), red; poly(6,6‘-bi-(9,9‘-dihexylfluorene)-co-(9,9‘-dihexylfluorene-3-thiophene-5‘-yl)) (PFT), green; and poly(9,9-dioctylfluorene-2,7-diyl) (PFO), blue. In order to overcome the complicated cascade energy transfer and deep trapping process, the two narrow band gap red and green light-emitting polymers are separated into two layers. In the bottom emission layer, hole-transporting material poly(N,N‘-bis(4-butylphenyl)-N,N‘-bis(phenyl)benzidine (poly-TPD) and electron-blocking material poly(N-vinylcarbazole) (PVK) were chosen to work together as binary-host; concomitantly, the novel red light-emitting polymer BE-co-MEH-PPV was employed as guest. In addition, in order to avoid phase separation in the top emission layer, two fluorene-deri...