Induction of Wurtzite to Zinc-Blende Phase Transformation in ZnSe Nanorods during Cu(I) Cation Exchange

We report the phase transfer in heavy-metal-free ZnSe nanorods (NRs) from hexagonal wurtzite (WZ) to cubic zinc-blende (ZB) phases. This phase transformation is mediated by Cu(I) ions under thermal heating, which reduce the energy barrier between the WZ and ZB phases of ZnSe. Cu(I) ions from CuI or CuCl precursors gradually enter the lattice of WZ ZnSe NRs and partially exchange Zn(II) ions to form nonstoichiometric alloyed CuZnSe NRs with a cubic ZB phase. A large excess amount of Cu(I) ions induces the fragmentation of the ZnSe NRs, resulting in the formation of short Cu-rich CuZnSe NRs with a peanut-like morphology after the ripening process. The alloyed CuZnSe NRs generate a localized plasmon surface resonance peak, which extends their light absorption to over 2200 nm, enabling the full-spectrum (UV-vis-NIR) absorption. The Cu(I)-induced phase transformation strategy demonstrated here provides a facile approach to synthesize ZB alloyed CuZnSe NRs and allows for the efficient full-spectrum solar energy harvesting by these nanostructures.