Effect of intrinsic strain on the optical band gap of single phase nanostructured Cu2ZnSnS4

Effect of intrinsic strain on the optical band gap of single phase Cu2ZnSnS4 (CZTS) nanostructures have been studied which have been synthesized by three different methods: ultrasonic assisted vapour deposition (UACVD), microwave and solvothermal in a single step process. X-ray diffraction and Raman studies revealed the formation of single phase CZTS nanostructures. The nanostructured film deposited by UACVD exhibited crystallite size ~20 nm, optical band gap of 1.4 eV with intrinsic strain 5.2×10−4 whereas the nanostructures grown by solvothermal method have smaller crystal size (~7 nm) with higher intrinsic strain (~52.9×10−4). With increases in the crystallite size from 7 nm to 20 nm, the optical band gap of CZTS nanoparticles decreases from 1.72eV to 1.4 eV. The variation in the optical band gaps of the CZTS nanostructures cannot be fully accounted to the variation in the size of nanoparticles and it has been attributed to the intrinsic strain present in the CZTS nanostructures.