Synthesis, photoconductivity and self-assembly of wurtzite phase Cu2CdxZn1−xSnS4 nanorods

Abstract

Cu₂Cd_xZn_1−xSnS₄ is a likely interfacial layer in Cu₂ZnSnS₄/CdS based thin film solar cells. It is thus important to investigate and understand the photoresponse behaviour of Cu₂Cd_xZn_1−xSnS₄ in order to further improve the cell efficiency and to develop alternative buffer layer materials containing no heavy metals. We have synthesized monodispersed wurtzite phase Cu₂Cd_xZn_1−xSnS₄ nanorods over the entire composition range by a facile solution based method and observed a systematic increase of the nanorod aspect ratio with increasing cadmium concentration. On the other hand, the optical band gap of Cu₂Cd_xZn_1−xSnS₄ nanorods decreases linearly from 1.56 eV (x = 0) to 1.39 eV (x = 1). Smooth, uniform and dense nanorod thin films have been coated on Mo-coated glass substrates using nanorod dispersions as nano-inks by a spray deposition method. Current (I)–Voltage (V) measurements of the annealed films show the highest photoresponse for Cu₂Cd_0.75Zn_0.25SnS₄ composition. We further demonstrate that the dipole–dipole interaction between the solvent and the nanorods can be manipulated for long-range vertical self-assembly of the nanorods for the different compositions. This simple method is promising for large area coating of the absorber layer in thin film solar cells and can be extended for use with other technologically important materials.