Boron doped amorphous carbon (a-C:B) film for heterojunction carbonbased photovoltaic solar cells were successfully fabricated on n-type silicon using palm oil precursor by the influenced of low positive bias voltage in the range of 0-50 V. The rectifying curve were found for all samples under dark measurement revealed that those samples were p-type semiconductor. The +30 V was found the optimized of the electronic properties with the open circuit voltage, current density, fill factor and efficiency were approximately 0.259034 V, 1.299456 mA/cm 2 , 0.240011 and 0.080788 %, respectively. The conversion efficiency of a-C:B has been improved under the influenced of low positive bias.