Structural, optical, electrical properties and energy band diagram of Cu2ZnSiS4 thin films

- A new absorber layer Cu2ZnSiS4 is synthesized at a lower sulphurization time.
- The energy band diagram of this new material Cu2ZnSiS4 has been proposed.
- The observed upward band bending at GB in Cu2ZnSiS4 is opposite to that of CZTS.

Cu2ZnSiS4 thin film has been synthesized using co-sputtering technique followed by sulphurization at 800 °C for 20 min. The relatively lower time of sulphurization employed are advantageous over earlier reported work in which the same material has been prepared in bulk form with a sulphurization time of ~ 24 h. The structural, optical and electrical properties of Cu2ZnSiS4 have been studied using macroscopic and nanoscopic characterization methods. Raman results confirm the formation of Cu2ZnSiS4 phase and X-ray diffraction spectra shows that its diffraction pattern is similar to Sn based (Cu2ZnSnS4) kesterite phase. The direct band gap of this new material is found to be ~ 2.71 eV. The conductivity-temperature analysis in the high temperature range (380 K-150 K) shows hopping conduction via defect states to be the conduction mechanism. The average work function of this material is 4.92 eV and Kelvin probe force microscopy results show an upward band bending at grain boundaries in comparison to intra-grain. X-ray photoelectron spectroscopy confirms the + 4 oxidation state of Si in the Cu2ZnSiS4 thin film sample. Further, results of Kelvin probe force microscopy, UV-visible and Ultra-voilet photoelectron spectroscopy measurements have been used to obtain energy band diagram of this new material which also reveal p-type semiconducting nature of the Cu2ZnSiS4 and indicate its usefulness as a photoelectrochemical material.