Two dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current generation of electron or/and photon based systems. The ultrashort diffusion length of exciton arising from ultrafast relaxation and low carrier mobility greatly discounts the performance of excitonic devices. Phonon scattering and exciton localization are crucial to understand the modulation of exciton flux in two dimensional disorder energy landscape, which still remain elusive. Here, we report an optimized scheme for exciton diffusion and relaxation dominated by phonon scattering and disorder potentials in WSe2 monolayers. The effective diffusion coefficient is enhanced by > 200% at 280 K. The excitons tend to be localized by disorder potentials accompanied by the steadily weakening of phonon scattering when temperature drops to 260 K, and the onset of exciton localization brings forward as decreasing temperature. These findings identify that phonon scattering and disorder potentials are of great importance for long-range exciton diffusion and thermal management in exciton based systems, and lay a firm foundation for the development of functional excitonic devices.
Passivating
defects to suppress recombination is a valid tactic
to improve the performance of third-generation perovskite-based solar
cells. Pb0 is the primary defect in Pb-based perovskites.
Here, tris(pentafluorophenyl)borane is inserted between the perovskite
and spiro-OMeTAD layer in SnO2-based planar perovskite
solar cells. The incorporation of tris(pentafluorophenyl)borane can
effectively passivate Pb0 defects, decreasing recombination
at the surface of the perovskite film. Additionally, the modification
with tris(pentafluorophenyl)borane decreases the grain boundaries
quantity in the perovskite film, enhancing the transportation capability
of carriers. The resulting perovskite solar cell gets a high efficiency
of 21.42%. While the reference device without tris(pentafluorophenyl)borane
treatment acquires an efficiency of 19.07%. More importantly, the
stability tests manifest that incorporating tris(pentafluorophenyl)borane
in perovskite solar cells is conducive to the stability of the device.
Improvements in the light-harvesting capacity and the carrier extraction
are both significant to improve the photovoltaic performance of perovskite
solar cells (PSCs). It has been proved that local surface plasmon
resonance (LSPR) based on metallic nanostructures is practical for
capturing light to enhance light harvesting. Motivated by this, a
special shaped Au nanoparticle, e.g., nanooctahedrons (Au NOs), with
a broadband LSPR peak and a suitable size is controlled synthesized
and applied in a PSCs device. The power conversion efficiency of PSCs
is increased from 16.95 to 19.05% with a short-circuit current density
(J
sc) as high as 23.63 mA/cm2. Besides the enhanced light-trapping effect of Au NOs LSPR proved
by optical spectroscopy analysis, the Kelvin probe force microscopy
results show that Au NOs can also effectively reduce the surface potential
of the electron transport layer, which promotes effective photocarrier
extraction at the interfaces. This paper sheds light on the question
of how plasmon excitation and light localization might be used advantageously
in high-efficiency photovoltaics.
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