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., Al 2 O 3 –HfO 2 , HfO 2 –Y 2 O 3 , and Al 2 O 3 –Y 2 O 3 systems, by combinatorial pulsed laser deposition to evaluate and control the fixed charge, while interface states were kept constant with a SiO 2 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 Y 2 O 3 was positive while those in the HfO 2 and Al 2 O 3 were negative. In the Al 2 O 3 –Y 2 O 3 system, the fixed charge was significantly varied between -2.7 and 1.3×10 12 cm -2 with composition spread. The maximum negative charge was found in the Al 2 O 3 layer with a slight amount of Y 2 O 3 , while the maximum positive charge was realized with almost pure Y 2 O 3 . The fixed charge modifications were also found in the Al 2 O 3 –HfO 2 and HfO 2 –Y 2 O 3 systems. Additional oxidation after layer deposition also modified the fixed charge properties. The largest negative fixed charge of -3.1×10 12 cm -2 was found in approximately HfO 2 :Y 2 O 3 =1:1 after the annealing process, while the largest positive charge of 1.3×10 12 cm -2 was found for Y 2 O 3 with Al 2 O 3 incorporation. The passivation layers with controlled fixed charge can be promising materials for the high-quality passivation layer in crystalline silicon solar cells.