Application of n-type microcrystalline hydrogenated silicon oxide film to hetero-junction microcrystalline silicon solar cells

In this study, the effect of wide-gap n-type μc-Si_1-XO_X:H film on the performance of hetero-junction μc-Si:H solar cells has been investigated. We have developed n-μc-Si_1-XO_X:H films by RF-PECVD (13.56 MHz) using a gas mixture of silane (SiH₄), hydrogen (H₂), 1%-hydrogen-diluted phosphine (PH₃) and carbon dioxide (CO₂) at a low substrate temperature of about 200°C. It was found that optical band gap (E₀₄) of n-type μc-Si_1-XO_X:H films were increased to larger than 2.4eV with increasing CO₂/SiH₄ ratio and power density. Under the optimized condition, a film showed the E₀₄ of 2.38 eV, dark conductivity (σ_d) of 0.086 S/cm, activation energy of 0.076 eV and crystal volume fraction (X_C) of 37%. The effect of n-μc-Si_1-XO_X:H was confirmed by J-V characteristics and spectral response of the hetero-junction μc-Si:H solar cells. The short-circuit current (J_SC) was increased from 23.1 mA/cm² to 23.7 mA/cm² and the spectral response in the long wavelength region was increased. Even if this observation needs further confirmation, our study demonstrated that wide-gap n-type μc-Si_1-XO_X:H films is beneficial for improving the performance of hetero-junction μc-Si:H solar cells.