Growth kinetics and mechanisms of multinary copper-based metal sulfide nanocrystals

Multinary copper-based metal sulfide (Cu-M-S) nanocrystals (NCs) usually have high absorption coefficients and near-optimum direct band gaps, which have been considered as novel photo-absorption materials for quantum dot-sensitized solar cells (QDSCs) and hole-transport materials for perovskite solar cells (PSCs). However, the formation and phase transformation mechanisms of Cu-M-S NCs during the solution-based preparing approaches are complicated. Herein, Cu-M-S NCs, including Cu₂ZnSnS₄ (CZTS), Cu₂SnS₃ (CTS), CuInS₂ (CIS), and CuSbS₂ (CAS), have been synthesized through solution-based hot-injection methods. Their formation and phase transformation mechanisms have been studied in terms of the growth kinetics. An effective method has been proposed to investigate the formation mechanisms of Cu-M-S NCs. The results suggest that CZTS, CTS, and CIS NCs are formed through an inter-reaction between metal sulfides rather than the classical cation exchange reactions, and CAS NCs are formed based on the Cu_xS structure; these findings provide new insights into the formation of Cu-M-S NCs. In addition, the anisotropic or isotropic growth processes during the growth stage have been found to be the key issues in the formation of a zinc blende or wurtzite structure NCs, respectively, which can be controlled by tuning the relative reactivity of metal precursors.