Single Room Vhf-pecvd Preparation Of Microcrystalline Silicon Thin Film Solar Cell Research

Single-chamber systems normally have a mechanical simplicity, which becomes a favorable factor for reducing the capital cost and the maintenance downtime of manufacturing lines. In this thesis, we studied the cross-contamination problems and the ways to reduce the boron and phosphorus contamination. Finally, high-quality microcrystalline silicon (μc-Si:H ) materials and relatively high efficiency solar cells using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) were prepared in a single chamber. In detail, following studies have been finished.1. Through optimizing deposition parameters, high-quality microcrystalline silicon materials with suitable photosensitivity, (220) preferable orientation and low defects were fabricated. In order to decrease the cross-contamination, high-quality p-layer and n-layer with reduced B₂H₆ and PH₃ usage have been developed, respectively.2. The influence of boron on the properties of intrinsic microcrystalline silicon thin films was studied. The results of electrical and structural properties showed that the dark conductivity decreased with the increase of boron contamination and the photosensitivity indicated the opposite change. Activation energy also changed due to different boron contamination in these thin films. The boron contamination decreases the crystalline volume fraction (Xc) and weakens the (220) preferable orientation intensity. However, contamination is less serious to the materials prepared at relatively high power and high hydrogen dilution, with higher crystalline volume fraction (Xc) and the (220) preferable orientation.3. The influence of phosphorus on the properties of p-layer and i-layer was also investigated. The results of electrical and structural properties showed that the dark conductivity of p-layer decreased and i-layer indicated the opposite change. However, phosphorus contamination is less serious to the materials for p-layer and i-layer prepared after better 'burial' procedure by the subsequent p-layer.4. Different methods for controlling the boron contamination at the p/i interface for the deposition ofμc-Si:H solar cells in a single chamber system were studied. These treatments consist of an a-Si:H covering layer, aμc-Si:H covering layer, and a hydrogen plasma treatment between the deposition of the p and i layers. Aμc-Si:H covering layer and a hydrogen plasma treatment significantly reduces the boron contamination at the p/i interface. However, the hydrogen plasma with high energy ion impinging the growing surface deteriorate the device performance. So, the treatment time should be less than 1min.5. Forμc-Si:H solar cells, the hydrogen plasma treatment improves the short-circuit current density (Jsc) and the conversion efficiency of solar cells. The influence of boron on the properties ofμc-Si:H thin films with different crystalline volume fraction (Xc) is various. From the experimental results, we suggest the introduced buffer layer with high crystalline volume fraction (Xc) between the p-layer and i-layer depositions to reduce the boron contamination. This method can restore the short wavelength response forμc-Si:H solar cells made in a single-chamber system. Theμc-Si:H covering layer or the plasma with high energy ion impinging in the empty chamber is superior for reducing boron contamination and improving the solar cells performance.6. Finally, single junctionμc-Si:H solar cells with 6.39% conversion efficiency and double junction a-Si:H/μc-Si:H solar cells with 10.56% at a rate of 3.5(?)/s have been fabricated by VHF-PECVD in the single chamber(only bottom solar cell in a single chamber), respectively.