252 research outputs found
Feature issue introduction: halide perovskites for optoelectronics
This joint Optics Express and Optical Materials Express feature issue presents a collection of nine papers on the topic of halide perovskites for optoelectronics. Perovskite materials have attracted significant attention over the past four years, initially for their outstanding performance in thin film solar cells, but more recently for applications in light-emitting devices (LEDs and lasers), photodetectors and nonlinear optics. At the same time, there is still much more to learn about the fundamental properties of these materials, and how these depend on composition, processing, and exposure to the environment. This feature issue provides a snapshot of some of the latest research in this rapidly-evolving multidisciplinary field
First-principles study of the lattice dynamics of Sb2S3
We present a lattice dynamics study of orthorhombic antimony sulphide (Sb2S3)
obtained using density-functional calculations in conjunction with the
supercell force-constant method. The effect of Born effective charges is taken
into account using a mixed-space approach, resulting in the splitting of
longitudinal and transverse optical (LO-TO) phonon branches near the zone
center. Zone-center frequencies agree well with Raman scattering experiments.
Due to the slow decay of the interatomic force constants (IFC), a minimal 2x4x2
supercell (Pnma setting) with 320 atoms is crucial for an accurate
determination of the dispersion relations. Smaller supercells result in
artificial acoustic phonon softening and unphysical lifting of degeneracies
along high symmetry directions. We propose a scheme to investigate the
convergence of the IFC with respect to the supercell sizes. The phonon
softening can be attributed to the periodic images that affect the accuracy of
the force constants, and the truncation of long-ranged forces. The
commensuration of the q-vectors with the supercell size is crucial to preserve
degeneracies in Sb2S3 crystals.Comment: 7 pages 4 figures, 3 table
Feature issue introduction: halide perovskites for optoelectronics
This joint Optics Express and Optical Materials Express feature issue presents a collection of nine papers on the topic of halide perovskites for optoelectronics. Perovskite materials have attracted significant attention over the past four years, initially for their outstanding performance in thin film solar cells, but more recently for applications in lightemitting devices (LEDs and lasers), photodetectors and nonlinear optics. At the same time, there is still much more to learn about the fundamental properties of these materials, and how these depend on composition, processing, and exposure to the environment. This feature issue provides a snapshot of some of the latest research in this rapidly-evolving multidisciplinary field
Dicke superradiance requires interactions beyond nearest-neighbors
Photon-mediated interactions within an excited ensemble of emitters can
result in Dicke superradiance, where the emission rate is greatly enhanced,
manifesting as a high-intensity burst at short times. The superradiant burst is
most commonly observed in systems with long-range interactions between the
emitters, although the minimal interaction range remains unknown. Here, we
prove that for an arbitrary ordered array with only nearest-neighbor
interactions in all dimensions, the condition for a superradiant burst violates
the positivity of the density matrix and is thus not physically observable. We
show that Dicke superradiance requires minimally the inclusion of
next-nearest-neighbor interactions. For exponentially decaying interactions,
the critical coupling is found to be asymptotically independent of the number
of emitters in all dimensions, thereby defining the threshold interaction range
where the collective enhancement balances out the decoherence effects. Our
findings provide key physical insights to the understanding of collective decay
in many-body quantum systems, and the designing of superradiant emission in
physical systems for applications such as energy harvesting and quantum
sensing.Comment: 5 pages, 4 figure
Room Temperature Light-Mediated Long-Range Coupling of Excitons in Perovskites
Perovskites have been the focus of attention due to their multitude of
outstanding optoelectronic properties and structural versatility.
Two-dimensional halide perovskite such as (C_6H_5C_2H_4NH_3)_2PbI_4, or simply
PEPI, forms natural multiple quantum wells with enhanced light-matter
interactions, making them attractive systems for further investigation. This
work reports tunable splitting of exciton modes in PEPI resulting from strong
light-matter interactions, manifested as multiple dips (modes) in the
reflection spectra. While the origin of the redder mode is well understood,
that for the bluer dip at room temperature is still lacking. Here, it is
revealed that the presence of the multiple modes originates from an indirect
coupling between excitons in different quantum wells. The long-range
characteristic of the mediated coupling between excitons in distant quantum
wells is also demonstrated in a structure design along with its tunability.
Moreover, a device architecture involving an end silver layer enhances the two
excitonic modes and provides further tunability. Importantly, this work will
motivate the possibility of coupling of the excitonic modes with a confined
light mode in a microcavity to produce multiple exciton-polariton modes.Comment: 12 pages, 11 figure
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A room temperature low-threshold ultraviolet plasmonic nanolaser
Constrained by large ohmic and radiation losses, plasmonic nanolasers operated at visible regime are usually achieved either with a high threshold (102–104 MW cm−2) or at cryogenic temperatures (4–120 K). Particularly, the bending-back effect of surface plasmon (SP) dispersion at high energy makes the SP lasing below 450 nm more challenging. Here we demonstrate the first strong room temperature ultraviolet (~370 nm) SP polariton laser with an extremely low threshold (~3.5 MW cm−2). We find that a closed-contact planar semiconductor–insulator–metal interface greatly lessens the scattering loss, and more importantly, efficiently promotes the exciton–SP energy transfer thus furnishes adequate optical gain to compensate the loss. An excitation polarization-dependent lasing action is observed and interpreted with a microscopic energy-transfer process from excitons to SPs. Our work advances the fundamental understanding of hybrid plasmonic waveguide laser and provides a solution of realizing room temperature UV nanolasers for biological applications and information technologies.Chemistry and Chemical Biolog
Nonlinear optical response of Au nanorods for broadband pulse modulation in bulk visible lasers
Due to the lack of suitable optical modulators, directly generated Pr3+- and Dy3+-doped bulk visible lasers are limited in the continuous-wave operation; yet, pulsed visible lasers are only sparingly reported recently. It has been theoretically predicated that Au nanorods could modulate the visible light operation, based on the nonlinear optical response of surface plasmon resonance. Here, we demonstrate the saturable absorption properties of Au nanorods in the visible region and experimentally realized the pulsed visible lasers over the spectral range of orange (605nm), red (639nm), and deep red (721nm) with Au nanorods as the optical modulator. We show that Au nanorods have a broad nonlinear optical response and can serve as a type of broadband, low-cost, and eco-friendly candidate for optical switchers in the visible region. Our work also advocates the promise of plasmonic nanostructures for the development of pulsed lasers and other plasmonic devices
Hot carrier extraction in CH3NH3PbI3 unveiled by pump-push-probe spectroscopy
Halide perovskites are promising materials for development in hot carrier (HC) solar cells, where the excess energy of above-bandgap photons is harvested before being wasted as heat to enhance device efficiency. Presently, HC separation and transfer processes at higher-energy states remain poorly understood. Here, we investigate the excited state dynamics in CH3NH3PbI3 using pump-push-probe spectroscopy. It has its intrinsic advantages for studying these dynamics over conventional transient spectroscopy, albeit complementary to one another. By exploiting the broad excited-state absorption characteristics, our findings reveal the transfer of HCs from these higher-energy states into bathophenanthroline (bphen), an energy selective organic acceptor far above perovskite's band edges. Complete HC extraction is realized only after overcoming the interfacial barrier formed at the heterojunction, estimated to be between 1.01 and 1.08 eV above bphen's lowest unoccupied molecular orbital level. The insights gained here are essential for the development of a new class of optoelectronics
Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light-matter Interactions
Van der Waals (vdW) solids, as a new type of artificial materials that
consist of alternating layers bonded by weak interactions, have shed light on
fascinating optoelectronic device concepts. As a result, a large variety of vdW
devices have been engineered via layer-by-layer stacking of two-dimensional
materials, although shadowed by the difficulties of fabrication. Alternatively,
direct growth of vdW solids has proven as a scalable and swift way, highlighted
by the successful synthesis of graphene/h-BN and transition metal
dichalcogenides (TMDs) vertical heterostructures from controlled vapor
deposition. Here, we realize high-quality organic and inorganic vdW solids,
using methylammonium lead halide (CH3NH3PbI3) as the organic part (organic
perovskite) and 2D inorganic monolayers as counterparts. By stacking on various
2D monolayers, the vdW solids behave dramatically different in light emission.
Our studies demonstrate that h-BN monolayer is a great complement to organic
perovskite for preserving its original optical properties. As a result,
organic/h-BN vdW solid arrays are patterned for red light emitting. This work
paves the way for designing unprecedented vdW solids with great potential for a
wide spectrum of applications in optoelectronics
Highly Efficient Thermally Co-evaporated Perovskite Solar Cells and Mini-modules
The rapid improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has prompted interest in bringing the technology toward commercialization. Capitalizing on existing industrial processes facilitates the transition from laboratory to production lines. In this work, we prove the scalability of thermally co-evaporated MAPbI3 layers in PSCs and mini-modules. With a combined strategy of active layer engineering, interfacial optimization, surface treatments, and light management, we demonstrate PSCs (0.16 cm2 active area) and mini-modules (21 cm2 active area) achieving record PCEs of 20.28% and 18.13%, respectively. Un-encapsulated PSCs retained ∼90% of their initial PCE under continuous illumination at 1 sun, without sample cooling, for more than 100 h. Looking toward tandem and building integrated photovoltaic applications, we have demonstrated semi-transparent mini-modules and colored PSCs with consistent PCEs of ∼16% for a set of visible colors. Our work demonstrates the compatibility of perovskite technology with industrial processes and its potential for next-generation photovoltaics
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