Correlation between Performances of the a-Si Solar Cells and Properties of the i-Layers Deposited at Extremely High Rates by Atmospheric Pressure Plasma CVD

Abstract

The atmospheric pressure plasma CVD (AP-PCVD) process was applied to the fabrication of intrinsic layer (i-layer) of single-junction amorphous silicon (a-Si) solar cells. The i-layers were prepared with extremely high deposition rates in atmospheric pressure VHF (very high frequency) plasma of gas mixtures containing He, H2 and SiH4. The other layers were deposited by the conventional low-pressure techniques. The I-V characteristics and the spectral sensitivity under AM-1.5, 100mW/cm2 illumination, and the I-V characteristics in the dark state of the solar cells were investigated as functions of the deposition parameters of the i-layers such as input power, hydrogen concentration (H2/SiH4) and Substrate temperature. The energy conversion efficiency (η) of the solar cell was strongly affected by the optical absorption characteristic of the i-layer. η of 6.6% was achieved when the deposition rate of i-layer was 168nm/s. At this deposition rate, it might be possible by scanning substrate to form i-layer of the thickness of 0.3μm on the substrate of 1m×1m area in 350 seconds, which was nearly 10 times faster than that by the conventional low-pressure plasma CVD technique.