n-Type microcrystalline silicon oxide layer and its application to high-performance back reflectors in thin-film silicon solar cells

Abstract Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In this study, we developed n -type microcrystalline silicon oxide ( n -μc-SiO x ) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n -μc-SiO x films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n -μc-SiO x back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage ( V oc ) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n -μc-SiO x layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% ( V oc : 0.501 V, J sc : 27.4 mA/cm 2 , FF: 0.68) using the n -μc-SiO x back reflector.