(A) study on fabrication and performance improvement of amorphous silicon solar cells using photo-CVD method

Abstract

In this thesis, fabrication and performance improvement of p/i/n type a-Si: H based solar cells using photo-CVD method were investigated. Firstly, characteristics of amorphous and microcrystalline silicon based material such as intrinsic a-Si:H, boron-doped a-SiC:H, intrinsic and p-,n-doped mc-Si:H prepared by photo-CVD method were investigated. It was shown that the obtained films are high quality films to fabricate high performance a-Si:H based solar cells. Then, TCO/p/i/n/metal type a-Si:H solar cells were fabricated using those high quality films. Various new techniques such as post hydrogen treatment on boron doped a-SiC:H p-layer,TCO/p-a-SiC:H/p-μc-Si:H double p-layer configuration, and hydrogen content grading at p/i interface were proposed for the improvement of cell performance as follows. The post hydrogen treatment on boron-doped a-SiC:H film widely used as a p- layer of p/i/n type a-Si:H based solar cells were proposed to improve the film quality. By measuring the thickness, electrical, structural and optical properties of the films before and after hydrogen treatment, it was found that the boron-doped a-SiC:H film was simultaneously etched and passivated by the treatment. The performance of the cell with the hydrogen treated p-layer was improved by ~7% due to an increase in $V_oc$ and F.F. compared to that of the untreated cell, although the p-layer thickness was nearly identical in both cases. The increase in $V_oc$ and F.F. could be explained by an increase in the built-in potential due to a decrease in the film activation energy. This electrical property improvement was well explained by the passivation effect of a $SiH_oc$/SiH ratio decrease and a hydrogen content increase of the film calculated by FTIR spectra. These film changes by post hydrogen treatment were considered to occur in the bulk of the boron-doped a-SiC:H film. The TCO/p-a-SiC:H/p-μc-Si:H double p-layer configuration for a-Si:H based solar cells was proposed as a method to pre...