CHEMICAL-BATH ZNO BUFFER LAYER FOR CUINS2 THIN-FILM SOLAR-CELLS

ZnO buffer layers were grown by a chemical-bath deposition (CBD) in or d.er to improve the interface quality in p-CuInS2 based solar cells, t o improve the light transmission in the blue wavelength region, but al so as an alternative to eliminate the toxic cadmium. The process consi sts of immersion of different substrates (glass, CIS) in a dilute solu tion of tetraamminezinc II, [Zn(NH2)(4)](2+), complex at 60-95 degrees C. During the growth process, a homogeneous growth mechanism which pr oceeds by the sedimentation of a mixture of ZnO and Zn(OH), clusters f ormed in solution, competes with the heterogeneous growth mechanism. T he mechanism consists of specific adsorption of a complex Zn(II) follo wed by a chemical reaction. The last process of growth results in thin , hard, adherent and specularly reflecting films. The characterization of the deposited CBD-ZnO layers was performed by X-ray diffraction (X RD), optical transmittance, scanning electron microscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-deposited films on glass show hexagonal zincite structure with two preferred orientations (1 0 0) and (1 0 1). High optical transmit tance up to 80% in the near-infrared and part of the visible region wa s observed. The low growth rate of the films on CIS suggests an atomic layer-by-layer growth process.The device parameters and performance a re compared to heterojunction with a standard CdS buffer layer. (C) 19 98 Elsevier Science B.V. All rights reserved.