In Situ Assembly of Cu_<i>x</i>S Quantum-Dots into Thin Film: A Highly Conductive P-Type Transparent Film

Abstract

Copper sulfide (CuxS) nanocrystals ranging from ∼2 to 4 nm in diameter were in situ assembled on surface-functionalized substrates at room-temperature to realize novel transparent p-type conducting film that combines good optical transparency and high electrical conductivity. The CuxS film exhibited superior homogeneity, highly compact microstructure and good adhesion to quartz-glass and polyethylene substrates. Results of X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and electron diffraction revealed that the film consisted of uniform fine Cu7S4 nanocrystals with copper vacancies. Good optical transparency and large bandgap blue-shift were observed in the CuxS film attributed to the dominant quantum effect. The CuxS QD film turned out to be a p-type semiconducting film with a large conductivity up to 105 S·m−1 at room temperature, which originated from the numerous defects stabilized by grain boundaries. A mechanism of the CuxS QD film formation has been proposed based on the surface-induced nucleation and the in situ assembly of the CuxS QDs.