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 (100 MHz) 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/sub 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/sub c/, V/sub cc/ tends to decrease, while poly-Si with X/sub c/>50% with (220) preferential orientation is necessary for high J/sub sc/. From the opposite dependence of V/sub oc/ and J/sub 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/sub c/ of 50%. So far now, we have obtained the maximum conversion efficiency of 6.9% (J/sub sc/=21.4 mA/cm/sup 2/, V/sub oc/=0.485 V, F.F.=0.665) with a 3-/spl mu/m thick i-layer at deposition rate of 3.1 /spl Aring//s.