posted on 2021-06-10, 16:36authored byChenghui Xia, Christina H. M. van Oversteeg, Veerle C. L. Bogaards, Tim H. M. Spanjersberg, Nienke L. Visser, Anne C. Berends, Johannes D. Meeldijk, Petra E. de Jongh, Celso de Mello Donega
Colloidal heteronanocrystals
allow for the synergistic combination
of properties of different materials. For example, spatial separation
of the photogenerated electron and hole can be achieved by coupling
different semiconductors with suitable band offsets in one single
nanocrystal, which is beneficial for improving the efficiency of photocatalysts
and photovoltaic devices. From this perspective, axially segmented
semiconductor heteronanorods with a type-II band alignment are particularly
attractive since they ensure the accessibility of both photogenerated
charge carriers. Here, a two-step synthesis route to Cu2–xS/CuInS2 Janus-type heteronanorods
is presented. The heteronanorods are formed by injection of a solution
of preformed Cu2–xS seed nanocrystals
in 1-dodecanethiol into a solution of indium oleate in oleic acid
at 240 °C. By varying the reaction time, Janus-type heteronanocrystals
with different sizes, shapes, and compositions are obtained. A mechanism
for the formation of the heteronanocrystals is proposed. The first
step of this mechanism consists of a thiolate-mediated topotactic,
partial Cu+ for In3+ cation exchange that converts
one of the facets of the seed nanocrystals into CuInS2.
This is followed by homoepitaxial anisotropic growth of wurtzite CuInS2. The Cu2–xS seed nanocrystals
also act as sacrificial Cu+ sources, and therefore, single
composition CuInS2 nanorods are eventually obtained if
the reaction is allowed to proceed to completion. The two-stage seeded
growth method developed in this work contributes to the rational synthesis
of Cu2–xS/CuInS2 heteronanocrystals
with targeted architectures by allowing one to exploit the size and
faceting of premade Cu2–xS seed
nanocrystals to direct the growth of the CuInS2 segment.