Bandgap engineering of Cu2InxZn1−xSn(S,Se)4 alloy films for photovoltaic applications

Bandgap engineering of Cu2InxZn1−xSn(S,Se)4 alloy films for photovoltaic application has been investigated. Cu2InxZn1−xSn(S,Se)4 (0 ≤ x ≤ 0.6) alloy films with different In contents and a single kieserite phase were fabricated by using a simple low-cost sol-gel method. The influence of In content on the structure, morphology, and optical and electrical properties of Cu2InxZn1−xSn(S,Se)4 films was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), X-Ray photoelectron spectroscopy (XPS), optical absorbance, and room-temperature Hall measurements. The results of XRD, TEM, and XPS demonstrated the substitution of some Zn atoms by In in Cu2InxZn1−xSn(S,Se)4 films. The Hall measurements show that the carrier concentration of the Cu2InxZn1−xSn(S,Se)4 (0 ≤ x ≤ 0.6) decreases with increasing In content and that the p-type Cu2InxZn1−xSn(S,Se)4 films with preferable electrical properties can be obtained by adjusting the In content during film deposition. The optical measurements indicate that the bandgap of Cu2InxZn1−xSn(S,Se)4 films with kesterite structure can be continuously tuned in the range of 1.13-1.01 eV as x is increased from 0 to 0.6. Our results show that the Cu2InxZn1−xSn(S,Se)4 alloy is a potentially applicable material for bandgap grading absorption layers in high-power-conversion-efficiency solar cells.