Abstract: The Photovoltaic device is fabricated by depositing the prepared polymer on the n-type silicon by spin coating method. The influence of thickness is noted in which the decrease in thickness led to an increase in efficiency of 30% cobalt’s chloride doped POT. The better efficiency of the prepared devices is increased by decreasing the thickness to be 3.224% at the thickness 39.75 nm for (Au/POT-30% cobalt’s chloride/n-type Si/Al ) with the open voltage circuit ( 0.48V ) , short circuit current ( 21.257mA/cm² ) and full factor ( 0.316 ) which are tested under illumination with intensity of 100mW/cm².