Thin-Film Solar Cell Absorber Cu2ZnSnS4 (CZTS) by Annealing of Monodisperse Kersterite Nanoparticle Precursors

Abstract

Indium in chalcopyrite-based solar cell absorbers can be substituted by zinc (Zn) and tin (Sn) forming a Cu2ZnSn(S,Se)4 (CZTS/CZTSe) absorber. Light to electricity conversion efficiencies of solar cells based on CZTSSe have recently reached over 9%, making this material competitive and more sustainable replacement for existing CdTe and Cu(In,Ga)Se2 (CIGS) thin-film technologies. The approach to grow CZTS using metal co-deposition of the Cu(II)– Zn(II)–Sn(IV) system followed by sulfurisation is very promising technique for large scale production. However the process suffers from the incomplete sulfurisation of the precursors, and requires the development of suitable rapid thermal processing technique for the formation of single CZTS phase similar to that of Cu-chalcopyrite solar absorber. In this work we report on the synthesis of uniform monodisperse CZTS nanoparticles at the temperature below 300 °C without the precipitation of secondary phases such as ZnS. The as-synthesized CZTS nanoparticles characterized by high resolution transmission electron microscopy (HR-TEM) exhibited highly crystalline structure with a size variation of 18.0±4.0 nm. The energy dispersive X-ray (EDX) analysis confirmed the presence of all elements with the atomic ratio of 43.3% S, 31.0% Cu, 14.9% Zn and 10.8% Sn. Thin films made from CZTS NPs are of kesterite structure and are greatly improved by annealing in Se/Ar atmosphere.