Thin film poly-Si formation for solar cells by Flux method and Cat-CVD method

Two methods were examined for the formation of poly-Si films. One is flux m ethod and the other is Cat-CVD method. Flux method was used for forming pol y-Si seed films on glass substrates covered with rear electrode. Poly-Si fi lms of a few mum grain size and of mainly (111) crystalline orientation wer e obtained at less than 600 degreesC. To make the seed films function as BS F layer for solar cell, boron doping was applied and carrier concentration of 2 x 10(19)/cm(3) was obtained which is suitable for highly efficient sol ar cells. Cat (catalytic)-CVD method was examined for forming poly-Si photo -active layers on the seed films. The films showed deposition gas pressure- dependent crystalline orientations and there was no amorphous incubation la yer in (111) oriented films by Cat-CVD method when deposited on(111) orient ed seed films prepared by Flux method. The electrical properties of the fil m are insufficient at present, may be due to high defect density and the fi lm structure which allows impurity contaminations of oxygen and carbon afte r film deposition. Although the film quality needs to be improved, poly-Si films whose crystal fraction is more than 85% were obtained at deposition r ate of up to around 40 Angstrom /s. This result indicates high potential of Cat-CVD method for high throughput photo-active formation process necessar y for low production cost thin him silicon solar cells. (C) 2001 Elsevier S cience B.V. All rights reserved.