Copper sulphide (CuS) nano-particles were employed in the hole transport layer (HTL) of thin film organic solar cells (TFOSC), to assist in the charge transport processes and improve the photons harvesting. Solar cells were fabricated in the standard bulk heterojunction device architecture using solar absorber composed of poly (3 hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend. The CuS nano-particles were dispersed in the aqueous solution of PEDOT:PSS, at concentrations varied from 0% to 0.15% by weight, to be able to determine the right doping level for the best solar cell performances. The particles exhibited surface plasmon resonance absorption and induced intense electric field that was beneficial to exciton dissociation. The highest power conversion efficiency found, in this investigation, was 4.51% at 0.10% CuS concentration in the HTL. This is an increase of 115% and 35% over the pristine PEDOT:PSS and CuS only HTLs used solar cells, respectively. Moreover, the solar cells fabricated with CuS doped PEDOT:PSS hole transport layers exhibited better environmental stability in ambient condition compared to those sole PEDOT:PSS or CuS HTLs. The newly fabricated devices were studied in terms of electrical and optical properties of the solar absorber layers.