Thin film polycrystalline silicon solar cells on mullite ceramics

In this work, we present the structural quality of polycrystalline silicon films formed by high-temperature chemical vapor deposition (CVD) on mullite ceramics coated with spin-on flowable oxides (FOx) serving as intermediate layers (ILs). The average grain size and the size distribution were investigated by optical microscopy. It is found that more than 65% of the surface of polysilicon films grown on boron-doped FOx is covered by large grains of 5–10μm. The intra-grain and inner-grain defects as well as the grain orientation were analyzed with the electron backscattering diffraction (EBSD) technique. Twin-type defects such as Σ3 and Σ9 are frequently present in these silicon layers, which are slightly (110) preferentially oriented. Finally, we present the photovoltaic data on test solar cells made on these CVD polysilicon films. An efficiency of about 3.3% is reported. The limiting factors, as well as possible improvements, are discussed.