Cu2ZnSnS4 Films Grown on Flexible Substrates by Dip Coating Using a Methanol-Based Solution: Electronic Properties and Devices

Abstract

The deposition of device quality Cu2ZnSnS4 (CZTS) films on flexible substrates by simple and cost-effective techniques is of great interest for solar cell applications. In this work, CZTS films were deposited on lightweight flexible substrates by successive dip coating using a nontoxic, methanol-based precursor solution. The films were characterized by x-ray diffraction, energy dispersive x-ray analysis, scanning electron microscopy, atomic force microscopy, optical transmission spectroscopy, photocurrent spectroscopy and admittance spectroscopy. The films prepared by this technique have direct band gaps of 1.5–1.6 eV, a p-type resistivity of ~1 Ω cm, an acceptor concentration of ~1017 cm−3 and structural and morphological properties that are suitable for device applications. Four defect levels with activation energies of 5.4 meV, 18.8 meV, 70 meV, and 221 meV were detected in the films. All but the shallowest defect level were attributed to the native VCu, CuZn, and VSn acceptor-type defects. For further assessment of the films, Schottky barrier and heterojunction diodes were fabricated and characterized. The results signified that the device quality CZTS films can be synthesized by the dip-coating method used in this study.