Effect of Cd content and sulfurization on structures and properties of Cd doped Cu2SnS3 thin films

Abstract

In the present work, we fabricated solid solution of Cd in the Cu2SnS3 (CTS:Cd) and Cu2CdSnS4 (CCTS) thin film by Cd doping in the Cu2SnS3 (CTS) with a simple solution approach and sulfurization process, and investigated the effects of Cd content and sulfurization on crystalline structure and quality as well as bandgap (Eg). It was found that a face-centered cubic CTS (C-CTS) film with Eg of 0.82 eV can be prepared by the solution approach. The C-CTS transformed into CTS:Cd with tetragonal structures (T-CTS:Cd) when the Cd contents are in the range of 4.18–13.38 at%, and further transform into T-CTS:Cd and CdS as the Cd content is between 13.38 and 19.57 at%. The Eg can be tuned from 0.82 to 1.26 eV by changing the Cd doping content for the as-fabricated samples. The sulfurization process made the C-CTS dissolve into C-CTS and T-CTS, and the T-CTS:Cd transformed into the CCTS in the Cd content of 7.30–13.54 at%. A single phase of CCTS film with Eg of 1.37 eV was obtained in the content of 10.18–13.54 at%. The sulfurization process can change crystalline structure, improve crystalline quality and tune band gap of the CTS and CCTS films at the same Cd doping content compared with the as-prepared films. It is believed that the single phase of C-CTS, T-CTS:Cd and CCTS films will be promising absorber materials of solar cells.