Abstract
Colloidal semiconductor nanostructures have been widely investigated for several applications, which rely not only on their size but also on shape control. CuInS2 (often abbreviated as CIS) nanostructures have been considered as candidates for solar energy conversion. In this work, three-dimensional (3D) colloidal CIS nanoflowers and nanospheres and two-dimensional (2D) nanoplatelets were selectively synthesized by changing the amount of a sulfur precursor (tert-dodecanethiol) serving both as a sulfur source and as a co-ligand. Monodisperse CIS nanoflowers (~15 nm) were formed via the aggregation of smaller CIS nanoparticles when the amount of tert-dodecanethiol used in reaction was low enough, which changed towards the formation of larger (70 nm) CIS nanospheres when it significantly increased. Both of these structures crystallized in a chalcopyrite CIS phase. Using an intermediate amount of tert-dodecanethiol, 2D nanoplatelets were obtained, 90 nm in length, 25 nm in width and the thickness of a few nanometers along the a-axis of the wurtzite CIS phase. Based on a series of experiments which employed mixtures of tert-dodecanethiol and 1-dodecanethiol, a ligand-controlled mechanism is proposed to explain the manifold range of the resulting shapes and crystal phases of CIS nanostructures.
Highlights
Colloidal semiconductor nanostructures have been extensively investigated due to their size dependent electronic structure and their attractive optical properties [1,2]
The shape and size control has been enabled by the use of tert-dodecanethiol (t-DDT) which played a crucial role in the formation of CIS nanostructures reported here
CIS nanostructures with flower, platelet- and sphere-like shapes were synthesized via a colloidal method, by altering the injected amount of t-DDT reactant acting as both a sulfur precursor and a ligand
Summary
Colloidal semiconductor nanostructures have been extensively investigated due to their size dependent electronic structure and their attractive optical properties [1,2]. CuInS2 (often abbreviated as CIS) is a heavy metal-free and earth abundant ternary semiconductor, which has a direct band gap of ~1.5 eV and a Bohr exciton radius of ~4.1 nm [13]. It is a stable compound with a large extinction coefficient of ~105 cm−1 at 500 nm, [14] which makes it one of the best materials for solar energy conversion. We have developed a colloidal method to synthesize CIS nanostructures with different sizes, shapes and crystal phases, ranging from small nanoflowers and larger-sized nanospheres with chalcopyrite crystal structure, and NPLs in the wurtzite phase. The shape and size control has been enabled by the use of tert-dodecanethiol (t-DDT) which played a crucial role in the formation of CIS nanostructures reported here
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