2 research outputs found
Observation of Enhanced Hole Extraction in Br Concentration Gradient Perovskite Materials
Enhancing hole extraction inside
the perovskite layer is the key factor for boosting photovoltaic performance.
Realization of halide concentration gradient perovskite materials
has been expected to exhibit rapid hole extraction due to the precise
bandgap tuning. Moreover, a formation of Br-rich region on the tri-iodide
perovskite layer is expected to enhance moisture stability without
a loss of current density. However, conventional synthetic techniques
of perovskite materials such as the solution process have not achieved
the realization of halide concentration gradient perovskite materials.
In this report, we demonstrate the fabrication of Br concentration
gradient mixed halide perovskite materials using a novel and facile
halide conversion method based on vaporized hydrobromic acid. Accelerated
hole extraction and enhanced lifetime due to Br gradient was verified
by observing photoluminescence properties. Through the combination
of secondary ion mass spectroscopy and transmission electron microscopy
with energy-dispersive X-ray spectroscopy analysis, the diffusion
behavior of Br ions in perovskite materials was investigated. The
Br-gradient was found to be eventually converted into a homogeneous
mixed halide layer after undergoing an intermixing process. Br-substituted
perovskite solar cells exhibited a power conversion efficiency of
18.94% due to an increase in open circuit voltage from 1.08 to 1.11
V and an advance in fill-factor from 0.71 to 0.74. Long-term stability
was also dramatically enhanced after the conversion process, i.e.,
the power conversion efficiency of the post-treated device has remained
over 97% of the initial value under high humid conditions (40–90%)
without any encapsulation for 4 weeks
Si/Ti<sub>2</sub>O<sub>3</sub>/Reduced Graphene Oxide Nanocomposite Anodes for Lithium-Ion Batteries with Highly Enhanced Cyclic Stability
Silicon
(Si) has attracted tremendous attention as a high-capacity anode material
for next generation Li-ion batteries (LIBs); unfortunately, it suffers
from poor cyclic stability due to excessive volume expansion and reduced
electrical conductivity after repeated cycles. To circumvent these
issues, we propose that Si can be complexed with electrically conductive
Ti<sub>2</sub>O<sub>3</sub> to significantly enhance the reversible
capacity and cyclic stability of Si-based anodes. We prepared a ternary
nanocomposite of Si/Ti<sub>2</sub>O<sub>3</sub>/reduced graphene oxide
(rGO) using mechanical blending and subsequent thermal reduction of
the Si, TiO<sub>2</sub> nanoparticles, and rGO nanosheets. As a result,
the obtained ternary nanocomposite exhibited a specific capacity of
985 mAh/g and a Coulombic efficiency of 98.4% after 100 cycles at
a current density of 100 mA/g. Furthermore, these ternary nanocomposite
anodes exhibited outstanding rate capability characteristics, even
with an increased current density of 10 A/g. This excellent electrochemical
performance can be ascribed to the improved electron and ion transport
provided by the Ti<sub>2</sub>O<sub>3</sub> phase within the Si domains
and the structurally reinforced conductive framework comprised of
the rGO nanosheets. Therefore, it is expected that our approach can
also be applied to other anode materials to enable large reversible
capacity, excellent cyclic stability, and good rate capability for
high-performance LIBs