10 research outputs found
Physicochemical properties of hybrid graphene-lead sulfide quantum dots prepared by supercritical ethanol
Recently, hybrid graphene–quantum dot systems have attracted increasing attention for the next-generation optoelectronic devices such as ultrafast photo-detectors and solar energy harvesting. In this paper, a novel, one-step, reproducible, and solution-processed method is introduced to prepare hybrid graphene–PbS colloids by employing supercritical ethanol. In the hybrid nanocomposite, PbS quantum dots (~3 nm) are decorated on the reduced graphene oxide (rGO) nanosheets (~1 nm thickness and less than 1 micron lengths). By employing X-ray photoelectron and Raman and infrared spectroscopy techniques, it is shown that the rGO nanosheets are bonded to PbS nanocrystals through carboxylic bonds. Passivation of {111} planes of PbS quantum dots with rGO nanosheets is demonstrated by employing density function theory. Quenching of the photoluminescence emission of PbS nanocrystals through coupling with graphene sheets is also shown. In order to illustrate that the developed preparation method does not impair the quantum efficiency of the PbS nanocrystals, the photovoltaic efficiency of solar cell device is reported and compared with oleic acid-capped PbS colloidal quantum dot solar cells. By employing the “Hall effect” measurement, it is shown that the carrier mobility is significantly increased (by two orders of magnitudes) in the presence of graphene nanosheets
Quasi Core/Shell Lead Sulfide/Graphene Quantum Dots for Bulk Heterojunction Solar Cells
Hybrid
nanostructures combining semiconductor quantum dots and
graphene are attracting increasing attention because of their optoelectronic
properties promising for photovoltaic applications. We present a hot-injection
synthesis of a colloidal nanostructure which we define as quasi core/shell
PbS/graphene quantum dots due to the incomplete passivation of PbS
surfaces with an ultrathin layer of graphene. Simulation by density
functional theory of a prototypical model of a nonstoichiometric Pb-rich
core (400 atoms) coated by graphene (20 atoms for each graphene sheet)
indicates the possibility of surface passivation of (111) planes of
PbS with graphene resulting in a decrease in trap states and recombination
sites. The graphene coating of the PbS quantum dots decreases the
exciton lifetime up to 0.78 ÎĽs as compared to 1.2 ÎĽs for
the oleic acid passivated PbS quantum dots due to the fast extraction
of carriers. We have employed PbS/graphene as well as Cd-doped PbS/graphene
quantum dots as active layers of bulk heterojunction solar cells,
and we achieved solar power conversion efficiencies of 3.6 and 4.1%,
respectively