Efficiency improvements in solution-based CuInS 2 solar cells incorporating a Cl-doped ZnO nanopillars array

Abstract

Solar cells are prepared combining ZnO as n-type window In2S3 as buffer layer and CuInS2 as p-type absorbing layer. Superstrate configuration is chosen so that all the materials could be prepared using inexpensive and eco-friendly techniques, based on solution processed deposition methods and non-toxic materials, avoiding vacuum high temperature Cd-containing layers and KCN purification stages. Also, no further sulfurization treatment is involved in the preparation. To improve the collection efficiency, the cells are built using two different ZnO nanostructures (with and without Cl-doping) and compared to the response of a cell prepared with just one dense ZnO layer. The photoresponse of the three different solar cells is analysed by J–V curves under illumination and intensity-modulated photovoltage/photocurrent spectroscopy. A systematic characterization of the morphology and composition is carried out using X-ray diffraction Raman confocal and electronic microscopy. The introduction of a nanostructured layer is not enough to produce a marked improvement in any of the electrical parameters. Instead, the presence of Cl-doped nanopillars is shown to increase the efficiency of the solar cells up to a maximum value of 2.8%. A better series resistance together with a higher value for the charge collection efficiency contributes to explain the corresponding improvement in cell efficiency.