Research On The Preparation And Properties Of Amorphous Silicon Carbide Films For Solar Cells

High efficiency and low cost crystalline silicon solar cells are very important for the large-scale application of solar energy. Preparation of the anti-reflection passivation film with excellent performance is one of the most important processes in the production of high-efficiency crystalline silicon solar cells. Besides the reduction of the sunlight reflection, the anti-reflection passivation films also play an important role in the surface passivation and effective improvement of the cell conversion efficiency.This work studies a new anti-reflection and passivation film-hydrogenated amorphous silicon carbide thin film. By using PECVD method and the precursors of silane and methane, hydrogenated amorphous silicon carbide thin film with excellent anti-reflective and passivation effects was prepared. First, the effects of deposition temperature, the flow ratio of silane to methane and the RF power on the surface morphology, chemical structure and optical properties of hydrogenated amorphous silicon carbide thin films were systematically studied. Then, the film formation mechanism and models were discussed. Secondly, the anti-reflection effects of hydrogenated amorphous silicon carbide thin films used in solar cells were studied. Finally, we studied the passivation of hydrogenated amorphous silicon carbide thin films prepared on different substrates. According to our studies, the main results are as follows:1. Morphology, chemical structure and optical properties are greatly affected by substrate temperature, the flow ratio of SiH4/CH4 and RF power of PECVD. It was found that, the density of as-deposited films increased, content of Si-C bond increased, the deposition rate decreased, the refractive index increased and the optical band gap decreased with the increase of substrate temperature. As the flow ratio of SiH4/CH4 increased, the deposition rate decreased, the optical band gap was wider, and the roughness first decreased and then increased. When flow ratio of SiH4/CH4 was 1:2, the densest film was obtained. With the increase of RF power, the density of as-deposited films increased, content of Si-C bond increased, the refractive index increased, the optical band gap was wider, and the deposition rate first increased and then stabilized.2. The anti-reflective properties of hydrogenated amorphous silicon carbide thin films were studied and discussed. Orthogonal experimental results show that the optimal experimental conditions of prepared optimization anti-reflective thin films were:substrate temperature is 250℃, flow rate ratio is 1:3, and RF power is 35 W. Under the guidance of orthogonal experimental results, we studied the anti-reflective properties of the thin films prepared under optimal conditions. We found that hydrogenated amorphous silicon carbide thin film has very low reflectivity and good transmission. In comparison of the SiN and SiC thin films, we found that SiC thin films have the same anti-reflective nature as SiN thin films.3. Hydrogenated amorphous silicon carbide thin film can enhance the minority carrier lifetime as well as the dual role of surface passivation and bulk passivation. As the substrate temperature increased, the minority carrier lifetime of substrate increased significantly and the passivation effect of thin film was strengthened. When the substrate temperate was 300℃, the best passivation effect was obtained, and then decreased. The passivation effect increased with the increase of the flow ratio of SiH4/CH4. With the increase of RF power, the passivation effect didn't change regularly. Minority carrier lifetime of both monocrystalline silicon and polycrystalline silicon samples increased a little.