We investigated the effect of thermal annealing on the properties of a-SiCN:H films prepared by HWCVD using hexamethyldisilazane focusing on the change in the passivation quality. We found that annealing a-SiCN:H films at the temperature around 600 degrees C led to an effective hydrogen diffusion, resulting in the enhancement of the passivation effect. The performance of cast polycrystalline silicon solar cells using a-SiCN:H films showed a strong dependence on the contact firing temperature. The best efficiency of 13.75% was achieved at the firing temperature of 750 degrees C. (C) 2007 Elsevier B.V. All rights reserved.