Abstract
Thin films of Cu2ZnSnS4 (CZTS) were synthesized via a low cost, wet chemical technique of chemical bath deposition (CBD). In the first part of this study, the chemical composition ratio S/(Cu+Zn+Sn) was varied keeping Cu/(Zn + Sn) and Zn/Sn ratios constant to study the effect of sulfur variation. Detailed electrical and optical characterization has been carried out using UV-visible spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy and Kelvin probe force microscopy (KPFM) techniques. The results of the present study confirm that near ideal stoichiometry could be achieved in CZTS by adding excess thiourea in a controlled manner which eliminated the need for an additional step of sulfurization. Using the stoichiometric sample as the basis, in the second part of the study Cu/(Zn+Sn) and Zn/Sn was varied and it was found that the electronic properties of CZTS in terms of band gap, work function and valence band edge position could be controlled by precursor variation. KPFM was used to qualitatively evaluate the photoresponse of the films and the Cu-poor, Zn-rich samples showed the best photoresponse out of all the samples which has been attributed to a decrease in the CuZn type defects. The study thus demonstrates a scalable and low-cost technique to grow CZTS absorber layers for solar cells with control over its electronic properties which is important for effective device operation.
•Stoichiometric CZTS films have been synthesized by a low cost, wet chemical method.•The films do not require post-synthesis high temperature sulfurization.•Band structure of the material has been controlled by precursor variation.•KPFM has been used to qualitatively evaluate photoresponse of films.•Improved photoresponse attributed to decrease in CuZn type antisite defects.