In this work, planar heterojunction organic photovoltaic cells (PHJ-OPVs) based on alpha-sexithiophene (alpha-6T) and fullerene active materials were investigated. We have studied the effect of the hole transporting layer (HTL) on the performances of the PHJ-OPVs. The studied HTLs are molybdenum trioxide (MoO3), cuprous iodide CuI and MoO3 & nbsp;coupled with CuI (MoO3/CuI). The PHJ-OPVs were fabricated using the thermal evaporation/sublimation technique. The experimental study shows that double HTL MoO3/CuI, using 1.5 nm of CuI thickness, improves significantly the efficiency of the PHJ-OPVs compared with those with single HTLs. This enhancement is due to the fact that MoO3 & nbsp;contributes to the optimization of the holes collection and CuI causes significant influence on the nucleation and the growth of alpha-6T. CuI has led to spectacular modification of the structural properties of alpha-6T. When alpha-6T is deposited onto ITO/MoO3, the alpha-6T layers are amorphous, while they are crystallized into monoclinic crystalline structure with a laying down molecular orientation when they are deposited onto ITO/MoO3/CuI. The use of the double HTL and the optimization of the alpha-6T deposition parameters have led to an important improvement in the alpha-6T light absorption, roughness and the holes mobility. These findings participated in the significant enhancement of the PHJ-OPVs performances and their life time.