Thin film poly-Si solar cells prepared by PECVD using very high excitation frequency

Thin film n-i-p solar cells with poly-Si i-layer grown by VHF-PECVD (100MHz) have been investigated. Change in deposition rate is explained in terms of the results of the plasma diagnostics. At low deposition rate regime, poly-Si with high crystalline volume fraction, X-c, is obtained. It is found that the crystalline volume fraction plays a predominant role in determination of photovoltaic performances. With an increase in X-c, V-proportional to tends to decrease, while poly-Si with X-c > 50% with (220) preferential orientation is necessary for high J(sc). From the opposite dependence of V-proportional to and J(sc) on the crystalline volume fraction, we found the most suitable deposition conditions in this series, and the obtained PV layer possesses relative low X-c of 50%. So far now, we have obtained the maximum conversion efficiency of 6.9% (J(sc) = 21.4 mA/cm(2), V-proportional to = 0.485 V, F.F. = 0.665) with a 3-mum thick i-layer at deposition rate of 3.1 A/s.