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

Abstract

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.