Material Research on High-Quality Passivation Layers with Controlled Fixed Charge for Crystalline Silicon Solar Cells

We evaluated the three types of composition spread passivation layer, i.e., Al₂O₃–HfO₂, HfO₂–Y₂O₃, and Al₂O₃–Y₂O₃ systems, by combinatorial pulsed laser deposition to evaluate and control the fixed charge, while interface states were kept constant with a SiO₂ interlayer. The flat-band voltage of the capacitance–voltage (C–V) curves was shifted widely from positive to negative by changing the composition. The calculated fixed charge in the Y₂O₃ was positive while those in the HfO₂ and Al₂O₃ were negative. In the Al₂O₃–Y₂O₃ system, the fixed charge was significantly varied between -2.7 and 1.3×10¹² cm^-2 with composition spread. The maximum negative charge was found in the Al₂O₃ layer with a slight amount of Y₂O₃, while the maximum positive charge was realized with almost pure Y₂O₃. The fixed charge modifications were also found in the Al₂O₃–HfO₂ and HfO₂–Y₂O₃ systems. Additional oxidation after layer deposition also modified the fixed charge properties. The largest negative fixed charge of -3.1×10¹² cm^-2 was found in approximately HfO₂:Y₂O₃=1:1 after the annealing process, while the largest positive charge of 1.3×10¹² cm^-2 was found for Y₂O₃ with Al₂O₃ incorporation. The passivation layers with controlled fixed charge can be promising materials for the high-quality passivation layer in crystalline silicon solar cells.