Influence of blending and conductive layer on the photoluminescence intensity of PFO thin films implemented for polymer light-emitting applications

Poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), referred to as light-emitting polymer, was utilized in this study to synthesize thin films for polymer light-emitting applications (PLED). Three thin films named P1, P2 and P3 refer to three different ways of film fabrication. P1 consists of only PFO, P2 consists of brilliant blue FCF blend PFO, while P3 consists of PFO on polyaniline conductive layer; all these thin films were deposited onto ITO-coated glass substrates (20 Ω) using Doctor blade method. Toluene had been used as the solvent of PFO material. P1 exhibits the smoothest surface (6.43 nm), which is consistent with the FESEM result. The surface roughness increases dramatically in the case of P2 (63.00 nm) with the presence of valleys and high peak protuberance. The surface roughness continues to significantly increase (152.00 nm) with deeper valleys for P3. PL intensity of the thin films was found to be dependent on the structural properties, chemical composition and optical features of these films. Film absorption was shown to increase with surface roughness, resulting in increased PL intensity and replacement of chemical bonds. P3 exhibited the highest PL intensity at 439.7 nm, which is attributable to the relatively lower amount of oxygen in the film structure, increasing both surface roughness and absorption of the film, in addition to the substitution of chemical bonds. P2 displayed higher PL intensity than that of P1 as well. Thus, PFO blend and using a polyaniline conductive layer in the PFO film structure enhance the PL intensity, thereby improving the applicability of PFO films-based polymer light-emitting diodes (PLED).