Analysis on bowing and formation of Al doped P⁺ layer by changes of thickness of N-type wafer and amount of Al paste

In this study, in order to improve the efficiency of n-type monocrystalline solar cells with an Alu-cell structure, we investigate the effect of the amount of Al paste in thin n-type monocrystalline wafers with thicknesses of 120 μm, 130 μm, 140 μm. Formation of the Al doped p⁺ layer and wafer bowing occurred from the formation process of the Al back electrode was analyzed. Changing the amount of Al paste increased the thickness of the Al doped p⁺ layer, and sheet resistivity decreased; however, wafer bowing increased due to the thermal expansion coefficient between the Al paste and the c-Si wafer. With the application of 5.34 mg/cm² of Al paste, wafer bowing in a thickness of 140 μm reached a maximum of 2.9 mm and wafer bowing in a thickness of 120 μm reached a maximum of 4 mm. The study's results suggest that when considering uniformity and thickness of an Al doped p⁺ layer, sheet resistivity, and wafer bowing, the appropriate amount of Al paste for formation of the Al back electrode is 4.72 mg/cm² in a wafer with a thickness of 120 μm.