Solar Cells, 3 (1981) 341 - 353 341 GROWTH PATTERNS OF CHEMIPLATED Cu2_~S LAYERS IN CdS/Cu2S THIN FILM SOLAR CELLS SAJI SALKALACHEN, S. JATAR, A. C. RASTOGI and V. G. BHIDE National Physical Laboratory, Hillside Road, New Delhi - 110012 (India) (Received December 11, 1980; accepted December 16, 1980) Summary The kinetics of growth of chemiplated Cu2-xS films on thermally deposited and chemically etched CdS layers were investigated. Scanning electron microscopy examination of parent films revealed the usual columnar growth and pyramidal tops as in typical high efficiency cells, with an enhanced area factor of 2.5. During chemiplating, Cu2-xS growth occurs conformal to the grain surface but deep penetrations result along the grain edges. In the present studies, quantitative estimates of such growth behaviour are obtained by varying the ion exchange reaction parameters, particularly the dip period and the pH of the CuC1 bath. Results suggest that for a pH value of 4.6 the growth is parabolic in nature whereas in solutions of lower pH (about 3.4) a fast linear growth mechanism dominates. The textured morphology of the grain yields an expression for net Cu2_xS growth from which grain surface thickness and grain boundary penetration depths are evaluated. Resultant changes in junction area are shown to affect the normal- ized open-circuit voltage of the CdS-Cu2S junction. The spectral responses of encapsulated cells are given after growth patterns of the Cu2_~S layers. These studies reveal that the pH of the solution plays an active role in con- trolling the Cu2_xS growth processes and also in obtaining superior cell characteristics. 1. Introduction Efficient CdS/Cu2S thin film solar cells are generally prepared by chemically plating vacuum-deposited CdS layers in CuC1 solution at about 95 - 98 °C for a few seconds [1]. Before chemiplating, the CdS film surface is texturized to enhance its light absorption properties and to increase the active junction area [ 2]. The Cu2S film determines the CdS topostructure in the exchange reaction but its stoichiometry, thickness, homogeneity and, in turn, the junction photovoltaic properties are essentially determined by the 0379-6787/81/0000-0000/$02.50 © Elsevier Sequoia/Printed in The Netherlands