In this study, we
present the preparation of graphene quantum dots
(GQDs) and graphene oxide quantum dots (GOQDs). GQDs/GOQDs are prepared
by an easy electrochemical exfoliation method, in which two graphite
rods are used as electrodes. The electrolyte used is a combination
of citric acid and alkali hydroxide in water. Four types of quantum
dots, GQD1–GQD4, are prepared by varying alkali hydroxide concentration
in the electrolyte, while keeping the citric acid concentration fixed.
Variation of alkali hydroxide concentration in the electrolyte results
in the production of GOQDs. Balanced reaction of citric acid and alkali
hydroxide results in the production of GQDs (GQD3). However, three
variations in alkali hydroxide concentration result in GOQDs (GQD1,
GQD2, and GQD4). GOQDs show tunable oxygen functional groups, which
are confirmed by X-ray photoelectron spectroscopy. GQDs/GOQDs show
absorption in the UV region and show excitation-dependent photoluminescence
behavior. The obtained average size is 2–3 nm, as revealed
by transmission electron microscopy. X-ray diffraction peak at around
10° and broad D band peak at 1350 cm
–1
in Raman
spectra confirm the presence of oxygen-rich functional groups on the
surface of GOQDs. These GQDs and GOQDs show blue to green luminescence
under 365 nm UV irradiation.
The electronic structure of hybrid perovskite compositions of FA0.83 Cs0.17 PbI3−xBrx (x = 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5) is determined using ultraviolet photoelectron spectroscopy (UPS) and UV–Vis–NIR absorption spectroscopy. With the help of UPS, ionization potential and Fermi energy are determined, and using absorption measurements, bandgap values are obtained. It is observed that for FA0.83 Cs0.17 PbI3−xBrx, as the Br content increases, the bandgap increases. The UPS measurements confirm the n-type nature of all compositions. Additionally, the Hall measurements were carried out for the selected compositions and the n-type carrier concentrations were determined.
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