P-I INTERFACE ENGINEERING AND I-LAYER CONTROL OF HOT-WIRE A-SI-H BASED P-I-N SOLAR-CELLS USING IN-SITU ELLIPSOMETRY

In this paper we report on the effect of monitoring the i-layer region near the p-i interface with the help of in-situ kinetic and spectrosc opic ellipsometry on the performance of hot-wire deposited hydrogenate d amorphous silicon p-i-n solar cells. It is very clearly observed tha t the microstructure at the p-i interface region in terms of the Si-Si bond packing density and surface roughness significantly affects the cell performance. The filament temperature, T-Fil, Was the main parame ter varied to control the above mentioned two properties near the p-i interface as well as in the bulk i-layer. In order to achieve signific ant enhancement in the cell performance we extended the idea of the '' soft start'', earlier employed for the glow discharge deposited solar cells, to the hot-wire deposited i-layer. We were able to control the i-layer properties at the p-i interface and in the bulk independently and correlate these to the cell performance. It is shown that a major increase in cell performance can be achieved by improving the microstr ucture of the growing film directly at the p-i interface. Most interes tingly, no significant deterioration in cell efficiency has been obser ved if only the p-i interface was properly controlled but the i-layer was of lower quality. These results are also shown to be consistent wi th model calculations of a numerical simulation. Our results therefore provide a clue to prepare hot-wire a-Si:H based solar cells with high efficiency and in the whole at high growth rates, which is needed for a more economic a-Si:H solar cell production.