The fill factor (FF) is a key parameter in the analysis of the efficiency of the photovoltaic devices. For an ideal device, the fill factor is a function only of the ratio light-generated current/reverse saturation current  formula  and is not a function of the ideality factor (A). FF is a parameter which, in conjunction with open circuit voltage (Voc) and current density (Jsc), determines the maximum power from a photovoltaic device. Current density losses are attributed to reflection, glass absoption, TCO absorption, CdS absorption, and deep-penetration losses. In general open circuit voltage is limited by the dominant current transport mechanisms. This paper will analyze the photovoltaic parameters of the CdS/CdTe photovoltaic devices prepared by close space sublimation (CSS) with different thickness of absorber. Thin film CdS/CdTe photovoltaic devices were fabricated on glass plates with an area of 2 x 2 cm2 covered with a SnO2 layer with a conductivity of ~ 102W-1cm-1. SnO2 served as the transparent front contact to CdS. Both CdS and CdTe layers were grown sequentially without intermediate processing. CdS was 0, 42 mm thick and had the resistivity 2-3 W×cm and transparency above 85%. After the CdTe layer was deposited, the structures were held in either CdCl2:H2O saturated solutions and then annealed in the air at 4000C ±50C for 30 min. All devices were completed with a Ni contact, which was deposited by the thermal evaporation process in vacuum. Different photovoltaic devices were fabricated with different thickness of CdTe at a fixed substrate and source temperatures of 350oC±50C and 540oC±50C, respectively. Photovoltaic solar energy conversion of CdS/CdTe devices is investigated using current-voltage (J-V) and capacitance-voltage (C-V) characteristics over a temperature range of 300-400 K. Current-voltage characteristics show that the FF of the prepared CdS/CdTe devices is low in general and depends on the thickness of the absorber. With the decreasing of the thickness of CdTe layer, the J-V curves are quite linear, at higher voltages and the reverse saturation current decreases. Recombination in the depletion region reduces the fill factor through the increase in A-factor and the decrease in open circuit voltage. Series resistance (Rs) and shunt resistance (Rsh) also reduce the FF.