Investigation of Cu2ZnSnS4 thin film by scanning Kelvin force microscopy

Abstract

CZTS thin film has been grown on Mo-coated soda lime glass by co-sputtering the metal targets and post sulfurization in H₂S ambient. The structural, microstructural, compositional and optical properties have been studied using glancing incidence XRD, Raman spectroscopy, SEM, EDS, XRF and UV-Vis spectrophotometry. Local electrical transport measurements using conducting AFM show that for small bias voltage (-0.5 V), the dark negative currents flow mainly through grain boundaries (GBs) rather than grain interior. Kelvin probe force microscopic measurements (local surface potential) indicated positive surface potential in the vicinity of GBs in a Cu-deficient CZTS thin film. All measurements indicated that grain interior to GBs have a smaller effective band gap than the bulk, due to the composition change (Cu-vacancies or Cu_Zn anti site defects) at GBs. Electrical measurement revealed the presence of defects in the CZTS thin film.