Correlation between Morphological, Optical and Electrical Properties of ZnO:Al/ZnO Double Layers and the Cu(In,Ga)Se2 Solar Cell Efficiencies

Abstract

The morphological, optical and electrical properties of magnetron sputtered ZnO:Al/ZnO double layers are reported and their correlations with their respective Cu(In,Ga)Se₂ (CIGS) solar cell efficiencies are presented. The ZnO:Al/ZnO double layers were produced by using the established baseline RF process and plasma emission monitoring (PEM) DC reactive sputtering. The scanning electron microscope (SEM) and atomic force microscope (AFM) were employed for the surface morphological measurements. The charge carrier concentrations, mobilities and AC resistivities were deduced from Drude’s model. The DC resistivities were determined from the four-point probe measurements. Transmittance and reflectance measurements were done by using the UV-VIS-NIR Lambda 900 double beam spectrophotometer. The I-V characteristic technique was employed for the solar cell performances. The lowest AC and DC resistivities obtained were 3.69 and 10.37ohm.cm respectively. Transmittances approaching 90% have been recorded by the ZnO:Al/ZnO double layers. Lower CIGS solar cell efficiencies were those fabricated from ZnO:Al/ZnO double layers with non-uniform AFM surfaces.

Keywords: ZnO:Al/ZnO, Cu(In,Ga)Se₂, sputtering, efficiency, Drude model.