Stud-Shaped Cu₂S Nanowire Arrays: In Situ One-Step Synthesis and Optical Properties

Stud-shaped Cu₂S nanowire arrays (arrays arranged with nanowires that exhibit a sudden reduction in diameter from their tops) were synthesized in situ on copper substrates deposited with a copper film through a simple one-step solid–gas reaction method. By controlling the gas ratio in the solid–gas reaction, Cu₂S nanowire arrays with different morphologies were obtained. It was found that with the increase of oxygen ratio in the mixed gas, the diameter of the nanowire’s top gradually decreases, and the composition of the top is mainly Cu₃₁S₁₆. This finding revealed the growth mechanism of the Cu₂S nanowire arrays in solid–gas reaction. The stud-shaped Cu₂S nanowire arrays exhibited excellent light absorption performance over a wide range of wavelength from 240 nm to 700 nm. When the gas ratio of H₂S to O₂ was 1:0.8, the average light absorption value reached to 90%. Even when the gas ratio was 1:0, the minimum average light absorption value still reached to 80%. The bandgap of the stud-shaped nanowire arrays synthesized at a H₂S to O₂ ratio of 1:0.8 was 1.40 eV, which was much higher than that of the corresponding bulk material (1.24 eV). Moreover, the bandgap of the stud-shaped Cu₂S nanowire arrays decreased with the increase in the nanowire diameter. The above results indicate that the bandgap and light absorption properties of the stud-shaped nanowire arrays can be tuned by controlling the ratio of the two gases in the mixed gas, which is beneficial for their photovoltaic applications. Meanwhile, the analysis of the growth mechanism of the stud-shaped Cu₂S nanowire arrays has laid the foundation for the effective synthesis of other types of nanowire arrays.