PbS QDs and rGO-decorated PbS QDs induced optical properties variations on P3HT:PC₆₁BM composite thin films

PbS QDs and PbS QDs decorated with reduced graphene (rGO) are prepared by hot-injection method using PbO and hexamethyldisilathiane (HMDS) as Pb and S sources, respectively. PbS QDs and PbS QDs:rGO are used as an addition to poly(3-hexylthiophene-2,5-diyl):phenyl-C₆₁-butyric acid methyl ester (P3HT:PC₆₁BM) composite. The effect of their addition on the morphological, topographical and optical properties of spin-coated P3HT:PC₆₁BM thin films are investigated. These additions tune the films to be more homogenous and more flatness as investigated in terms of field scanning electron microscope. The topographical properties of the films are explored by atomic force microscope. The results show decreasing in the grain size and the surface roughness in P3HT:PbSQDs:PC₆₁BM film compared to other composites films. The optical properties of the films are studied over the spectral range 200–2500 nm. On one hand, the absorption coefficient of different films is computed and the optical band gap of the films is found to decrease after addition of PbS QDs and PbS QDs:rGO. On the other hand, the refractive index of the films is explained according to the single-oscillator model to get the dispersion parameters. In addition, the lattice dielectric constant and the ratio of the free-carriers concertation to their effective mass are evaluated.