Cobalt selenide clusters with 2-bromo-5-diethylphosphinothiophene (1) and 2-bromo-5-diphenylphosphinothiophene (2) ligands are described. The phosphine ligands are obtained via lithium halogen exchange of 2,5-dibromothiophene followed by addition of chlorodiethylphosphine and chlorodiphenylphosphine, respectively. The prepared phosphine ligands are then sequentially reacted with elemental selenium followed by dicobalt octacarbonyl to yield Co₆Se₈(P(Et)₂(C₄H₂SBr))₆ (3) or Co₆Se₈(P(Ph)₂(C₄H₂SBr))₆ (4), respectively. The two new cobalt selenide clusters were characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, cyclic voltammetry, powder X-ray diffraction, and elemental analysis. Emission spectra were recorded for the addition of, Co₆Se₈(PEt₃)₆ (5), 3, and 4 to a 0.004 wt% solution of poly-3-hexyl thiophene (P3HT) in toluene to investigate the charge transport of the system. The quenching of the polymers’ emission follows first-order like decay for each cluster. Clusters 3 and 4 are approximately twice as efficient at quenching the emission than cluster 5 with 4 being slightly more efficient than 3. Simple mixtures of 3, 4 or 5 and P3HT were spun cast from toluene into thin films and atomic force microscopy displayed relatively uniform dispersion of 3 and network-like formation of 4 in contrast to the phase separation of 5 in the polymer films.