Growth of Cu2ZnSnS4 thin films by hybrid chemical approach

Abstract

Thin films of Cu2ZnSnS4 (CZTS), an emerging solar cell absorber layer, were prepared by a hybrid chemical process followed by annealing. In this process, two binary layers, SnS and ZnS were grown sequentially using chemical bath deposition method (CBD) onto soda-lime glass substrates. Subsequently the ZnS layer was partly converted into CuxS layer through an ion-exchange process by immersing the stack glass/SnS/ZnS in CuCl2 solution. The resulting stack, namely glass/SnS/ZnS/CuS, was annealed in sulphur atmosphere at 450 °C for an hour to promote inter-diffusion of the layers leading to the formation of CZTS film through the solid-state reaction path. The stack with a ZnS layer of 470 nm thick and 270 nm thick SnS led finally to the desired CZTS phase formation. XRD analysis of these films showed CZTS peaks which are close to the Cu2SnS3 (CTS) phase. Raman spectra recorded to distinguish CTS and CZTS phases showed modes at 291, 338 cm−1 corresponding to CZTS phase confirming its formation. The band gap of CZTS films is found to be 1.42 eV. The films were found to be p-type in nature. An attempt is made to fabricate heterojunction solar cell.