Indium effect on structural, optical and electrical properties of Cu2InxZn1-xSnS4 alloy thin films for solar cell

The Cu2InxZn1-xSnS4 (0 ≤ x ≤ 0.8) alloy thin films were synthesized on soda lime glass (SLG) substrate by a simple low-cost sol-gel method. The influence of In content on the structural, morphology, optical and electrical properties of Cu2InxZn1-xSnS4 thin films was investigated by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), the scanning electron microscopy (SEM), optical absorbance and room-temperature Hall measurements. The results indicated that the crystal structure changed from tetragonal to the mixture of tetragonal and cubic, as x varied from 0 to 0.8. The tetragonal type structure of Cu2InxZn1-xSnS4 could be stabilized at x = 0.5 without cubic CuInSnS4 phase separation. Morphological analysis showed the grain size and crystallinity have been enhanced as the x value increased from 0 to 0.4. The Cu2InxZn1-xSnS4 alloy thin film at x = 0.4 showed the best p-type conduction characteristics with a hole concentration of 1.06 × 1015 cm−3 and a hall mobility of 6.65 cm2 V−1s−1. As the x increased to 0.5, the conductivity of films changed dramatically from p-to n-type. In addition, the optical band gap of Cu2InxZn1-xSnS4 alloy thin films with tetragonal kesterite could be continuously changed in range of 1.45-1.29 eV as the x value varied from 0 to 0.5. The Cu2InxZn1-xSnS4 alloy thin films should be ideal light-absorber material for achieving higher efficiency kesterite solar cells.