Heavy doping of S2 in Cu7.2S4 lattice into chemically homogeneous superlattice Cu7.2Sx nanowires: strong photoelectric response

Abstract

This is the first time a series of chemically homogeneous superlattice Cu_7.2S_x (x = 4.07, 4.52, 6.01, 6.20, 6.45) nanowires have been successfully synthesized by heavy doping of S₂ species in Cu_7.2S₄ lattice through a simple wet-chemical route. This superlattice structure is a polytypoid structure tuned by adjusting the atom ratio of S₂ to S in lattice configuration. The perfect superlattice Cu_7.2S_6.20 structure interestingly consists of two alternating lattice fringes corresponding to the atom layers of Cu–S and Cu–S₂ in an even spacing of 5.70 Å. The article describes the formation, morphology, composition and structure of the Cu_7.2S_x superlattice nanowires. Photoluminescence (PL) spectra and transient photovoltage (TPV) measurements reveal that the generation and separation efficiency of the photogenerated charges of Cu_7.2S_x nanowires could be greatly improved by adjusting the S₂/S ratio in the lattice configuration, and thus enhance the luminescence quantum efficiency. This study reveals that the S₂ species in Cu_7.2S_x nanowires play a very important role in determining the dynamic properties of photogenerated charge carriers.