Optimization of the back surface field (BSF) for crystalline silicon solar cells was carried out by Afors-Het simulation software. Thickness and doping concentration parameters were optimized and electrical parameters of solar cells both with BSF and non-BSF were analyzed. The optimum BSF thickness and doping concentration for the crystalline silicon solar cell were determined as 7 µm and 1x1019 cm-3, respectively. A special attention was given to the estimation of peak firing temperature considering the printing amount of aluminum paste in order to form an optimal BSF by the calculations using Al-Si binary phase diagram. It was concluded that the temperature of up to 950oC should be established if an amount of 3 mg/cm2 printed aluminum was used to achieve BSF thickness of 7 µm, where 775 oC would be enough when the amount of aluminum is 8 mg/cm2.