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INFLUENCE OF TRANSPARENT CONDUCTING OXIDE ON AMORPHOUS SILICON SOLAR CELL PERFORMANCE Chris Walker, Russell Hollingsworth, Joe del Cueto, Arun Madan. Glasstech Solar, Inc. (GSI), 12441 W. 49th Avenue, Wheatridge, CO 80033, U.S.A. INTRODUCTION The use of transparent conducting oxides (TCO) as electrical contacts in a-Si:H solar cells has stimulated interest in the multitude of effects that these layers have on a-Si:H solar cell performance. The study of a-Si:H p-i-n junctions using a TCO contact involves many factors such as, interdiffusion, transmission, reflection, and resistivity. In this paper, we attempt to distinguish between these factors through the role they play in determining the solar cell device performance. Devices were characterized via dark and illuminated current vs. voltage (I-V) measurements, and spectral response. It was found that the properties of the TCO have an important role in influencing FF and Jsc in the devices. EXPERIMENTAL For this study we have used a commercially available state-of-the art, multichamber ultra high vacuum system manufactured by GSI in which the effects of cross-contamination have been totally eliminated, since different amorphous semiconducting layers are deposited in different chambers. The system routinely produces high efficiency devices (approaching 11%) as evidenced by the data displayed in Table I. As the table shows, for intrinsic layer thicknesses of -8000A, the fill factors (FF) ars about .70 with short circuit density, Jsc around 17-18 mA/cm , indicating a long minority carrier diffusion length. Table I Voc (volts) 0.825 0.826 0.85 0.810 5.75

Jsc (mAcm 17.9 18.1 17.2 18.0 16.4

)

FF

No. of interconnected cells

0.717 0.668 0.69 0.63 0.62

1 1 1 1 7

Area (cm2

n(%)

0.08 0.08 1.48 5.80 40.6

10.6 10.0 10.1 9.2 8.3

We have investigated the performance of a-Si:H p-i-n solar cells on TCO provided by 8 different manufacturers, prepared using various deposition techniques with the requirements that Rsheet 15n/square f and the transmission (T) over the visible spectrum exceed 80%. The composition of the TCO was Sn0 2 :F in all instances except for the case of plasma enhanced reactively evaporated ITO material, which was deposited by evaporation of Indium-Tin alloy in an oxygen plasma onto a heated substrate.

Mat. Res. Soc. Symp. Proc. Vol. 70.

1986 Materials Research Society

564

Each of the samples was verified as satisfying the sheet resistance and transmission requirements. The transmission vs. wavelength response for the Sn0 2 :F samples was divided into a total transmission component using an integrating sphere attachment, and a specular transmission component. The surface topography of the TCO was examined by the use of an SEM. Several sets of a-Si:H p-i-n solar cells were deposited under various conditions, with groups of four to nine different TCO coated substrates undergoing co-deposition during each set. The a-Si:H p-i-n layer depositions were performed in a GSI glow discharge system using either a single chamber or a multichamber approach. Unles