Characteristics of Si ribbons grown by the S-web technique

Abstract Thin silicon ribbons have been grown with high throughput by the S-Web technique. The ribbons were up to 12 cm wide and up to 40 m long. The maximum pulling speed was 2 m/min. The crystal morphology and microelectrical properties were investigated by SEM and electron-beam-induced current. A twin structure of low electrical activity was found to be the predominant defect. Electron channeling pattern analyses have shown that a preferred orientation of the grain structure does not exist. Impurity contents were studied by infrared spectroscopy, secondary ion mass spectrometry, deep level transient spectroscopy and neutron activation analysis. The observed V-shaped impurity distribution across the ribbon thickness was explained by segregation and melt film drag out effects. Test solar cells showed efficiencies up to η = 12.0% with a mean value of ḡh ≈ 10.5%. The interaction of line and point defects with carbon and oxygen is believed to be the main factor presently limiting the solar cell efficiency. A pilot pulling unit was recently installed being capable of producing Si ribbons up to a width of 30 cm and a speed of several m/min.