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 _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_cc 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_oc 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/cm², V _oc=0.485 V, F.F.=0.665) with a 3-μm thick i-layer at deposition rate of 3.1 Å/s