Silicon was doped with Mg, Al, S,Cu, Zn and Cd. For Mg, Al,S and Zn with atomic numbers 12, 13, 16 and 30 the efficiency decreases to be 0.0960, 0.0650, 0.0560, and 0.0280. This decrease of efficiency due to atomic number increase may be attributed to the fact that increase of atomic number decreases atomic and free charge density which decreases current and decreases efficiency. For Cu and Cd the increase of atomic number from 29 to 48 decreases the energy gap from 5.184 to 5.107 which is related to the fact that increase of atomic number increases atomic radius which decreases the energy gap. The decrease of energy gap increases the efficiency to change from 0.0090 to 0.069.