We deposited a-SiCN:H films by HWCVD using a gas mixture of hexamethyldisilazane, H2 and N2, and fabricated cast polycrystalline silicon solar cells with the a-SiCN:H passivation and anti-reflection layer. N2 addition led to the reduction of the refractive index of the a-SiCN:H films due to the increase in nitrogen concentration of the films. This improved performance of the antireflection layer. The advantage of adding N2 to the process was demonstrated by the improvement in short circuit current (JSC) and efficiency of cast polycrystalline silicon solar cells. At present, the efficiency of cast polycrystalline silicon solar cell using a-SiCN:H film as a passivation layer reached 14.2%.