Perovskite Metasurfaces Research Articles

Realization of Polaritonic Topological Charge at Room Temperature Using Polariton Bound States in the Continuum from Perovskite Metasurface

AbstractExciton‐polaritons are mixed light–matter excitations resulting from the strong coupling regime between an active excitonic material and photonic resonances. Harnessing these hybrid excitations provides a rich playground to explore fascinating fundamental features, as out‐of‐equilibrium Bose–Einstein condensation and quantum fluids of light, plus novel mechanisms to be exploited in optoelectronic devices. The formation of exciton‐polaritons arising from the mixing between hybrid inorganic–organic perovskite excitons and an optical bound state in a continuum (BIC) of a subwavelength‐scale metasurface, are experimentally investigated at room temperature. These polaritonic eigenmodes, hereby called polariton BICs (pol‐BICs) are revealed in reflectivity, resonant scattering, and photoluminescence measurements. Although pol‐BICs only exhibit a finite quality factor bounded by the nonradiative losses of the excitonic component, they fully inherit BIC peculiar features: a full uncoupling from the radiative continuum in the vertical direction, which is associated to a locally vanishing farfield radiation in momentum space. Most importantly, the experimental results confirm that the topological nature of the photonic BIC is perfectly transferred to the pol‐BIC. This is evidenced by the observation of a polarization vortex in the farfield of polaritonic emission. The results pave the way to engineer BIC physics of interacting bosons and novel room temperature polaritonic devices.

Strong Coupling of Exciton and High‐Q Mode in All‐Perovskite Metasurfaces

AbstractRecently developed halide perovskite semiconductors are viewed as an excellent platform to realize exciton‐polariton at room temperature due to their large oscillation strength. Here, the optimized strong coupling between the exciton of perovskite and quasi‐bound state in the continuum (QBIC) with high‐quality factor (Q‐factor), supported by all‐perovskite metagrating, including magnetic dipole (MD)‐QBIC and toroidal dipole (TD)‐QBIC is demonstrated. By taking advantage of extreme electric field confinement enabled by a high‐Q mode, it is found that the maximum Rabi splitting can be enhanced up to a record high value of 400 meV, almost twice the Rabi splitting reported in the same perovskite‐based subwavelength metasurface. The simulation results reveal that both the Q‐factor of QBIC mode and the thickness of the perovskite metasurface play dominant roles in the enhanced strong coupling. It is also demonstrated that adding a protection layer of poly(methyl methacrylate) on the top of the perovskite metagrating has a negligible effect on the maximized Rabi‐splitting. These results suggest a new approach for studying exciton‐polaritons and may pave the way toward flexible, large‐scale, and low‐cost integrated polaritonic devices and the realization of polariton lasing at room temperature.

Enhanced Multiphoton Processes in Perovskite Metasurfaces.

Multiphoton absorption and luminescence are fundamentally important nonlinear processes for utilizing efficient light-matter interaction. Resonant enhancement of nonlinear processes has been demonstrated for many nanostructures; however, it is believed that all higher-order processes are always much weaker than their corresponding linear processes. Here, we study multiphoton luminescence from structured surfaces and, combining multiple advantages of perovskites with the concept of metasurfaces, we demonstrate that the efficiency of nonlinear multiphoton processes can become comparable to the efficiency of the linear process. We reveal that the perovskite metasurface can enhance substantially two-photon stimulated emission with the threshold being comparable with that of the one-photon process. Our modeling of free-carrier dynamics and exciton recombination upon nonlinear photoexcitation uncovers that this effect can be attributed to the local field enhancement in structured media, a substantial increase of the mode overlap, and the selection rules of two-photon absorption in perovskites.

Thermal Transport in Engineered Hybrid Organic–Inorganic Perovskite Metasurfaces

Halide perovskites have recently gained widespread attention for their exceptional optoelectronic properties which have been illuminated by extensive spectroscopic investigations. In this article, nanophotonic surface-engineering using soft-lithography has been used to reproduce nanostructures with enhanced functionalities. A non-invasive optical technique based on Raman and photolumines-cence (PL) spectroscopy is employed to investigate the interactive effect of the thermal and optical behaviour in surface-patterned hybrid organic-inorganic halide perovskite thin films. The thermophys-ical properties of the engineered perovskite films are extracted from the softening of the representa-tive peak positions in the Raman and PL spectra of the samples which act as temperature markers. The investigation suggests a comparatively higher rise in the local temperature for the patterned thin films resulting from their enhanced absorption. Therefore, a cross-talk between the opto-thermal transport phenomena in imprinted perovskite thin films pertaining to both enhancing device properties along with maintaining device stability is established.

Engineering a light–matter strong coupling regime in perovskite-based plasmonic metasurface: quasi-bound state in the continuum and exceptional points

We present theoretically the formation of exciton–photon polaritons and exciton-surface plasmon polaritons in a perovskite-based subwavelength lattice on the metallic plane. It is shown that the later polaritons will be achieved as the perovskite layer is ultra-thin ( < 50 nm ), while the co-existence of both polaritons will dominate, as the thickness of the perovskite metasurface approaches wavelength-scale. In the two cases, the lower polaritonic branches consist of dark and bright modes corresponding to infinite and finite radiative quality factors, respectively. Another salient property in this work is that it allows one to obtain exceptional points (EPs) in momentum space with a four-fold enhancement of local density of states through engineering the perovskite metasurface. Our findings show that the perovskite metasurface is an attractive and rich platform to make polaritonic devices, even with the presence of a lossy metallic layer.

Broadband Antireflection with Halide Perovskite Metasurfaces

AbstractMeta‐optics based on optically resonant dielectric nanostructures is a rapidly developing research field with many potential applications. Halide perovskite metasurfaces have emerged recently as a novel platform for meta‐optics, and they offer unique opportunities for control of light in optoelectronic devices. Here, the generalized Kerker conditions are employed to overlap electric and magnetic Mie resonances in each meta‐atom of MAPbBr3 perovskite metasurface, and broadband suppression of reflection down to 4% is demonstrated. Furthermore, it is revealed that metasurface nanostructuring is also beneficial for the enhancement of photoluminescence. These results may be useful for applications of nanostructured halide perovskites in photovoltaics and semi‐transparent multifunctional metadevices where reflection reduction is important for their high efficiency.

Soft Lithography for Manufacturing Scalable Perovskite Metasurfaces with Enhanced Emission and Absorption

AbstractOrganic–inorganic hybrid perovskites have emerged in recent years as a promising alternative to silicon solar cells and other optoelectronic devices, mostly due to their high photon yields, long carrier lifetime, adjustable bandgap, and other merits. While patterning photonic nanostructures onto their inorganic counterparts is well established to augment their capabilities, lack of compatibility with conventional lithography techniques hinders the implementation of those principles with perovskites. Hereby, the fabrication of MAPbI3 nanophotonic structures such as nanoscale metasurfaces is demonstrated via soft lithography, a method in which the patterning is done when the perovskite is not fully crystallized, allowing for crystallization within the mold with the end result of facile and unharmful imprinting of sub‐micron features onto perovskite thin films, over large areas and with the potential to scale up in a seamless way. By doing so, a substantial increase in light absorption as well as twofold photoluminescence enhancement from the perovskite thin film is shown. These results are supported by spectral and lifetime measurements. This method is pertinent to many device configurations and can assist in realizing the future of high‐efficiency perovskite‐based devices, including solar cells, LEDs, lasers, and more.

Plasmonic Metasensors Based on 2D Hybrid Atomically Thin Perovskite Nanomaterials.

In this work, we have designed highly sensitive plasmonic metasensors based on atomically thin perovskite nanomaterials with a detection limit up to 10−10 refractive index units (RIU) for the target sample solutions. More importantly, we have improved phase singularity detection with the Goos–Hänchen (GH) effect. The GH shift is known to be closely related to optical phase signal changes; it is much more sensitive and sharp than the phase signal in the plasmonic condition, while the experimental measurement setup is much more compact than that of the commonly used interferometer scheme to exact the phase signals. Here, we have demonstrated that plasmonic sensitivity can reach a record-high value of 1.2862 × 109 µm/RIU with the optimum configurations for the plasmonic metasensors. The phase singularity-induced GH shift is more than three orders of magnitude larger than those achievable in other metamaterial schemes, including Ag/TiO2 hyperbolic multilayer metamaterials (HMMs), metal–insulator–metal (MIM) multilayer waveguides with plasmon-induced transparency (PIT), and metasurface devices with a large phase gradient. GH sensitivity has been improved by more than 106 times with the atomically thin perovskite metasurfaces (1.2862 × 109 µm/RIU) than those without (918.9167 µm/RIU). The atomically thin perovskite nanomaterials with high absorption rates enable precise tuning of the depth of the plasmonic resonance dip. As such, one can optimize the structure to reach near zero-reflection at the resonance angle and the associated sharp phase singularity, which leads to a strongly enhanced GH lateral shift at the sensor interface. By integrating the 2D perovskite nanolayer into a metasurface structure, a strong localized electric field enhancement can be realized and GH sensitivity was further improved to 1.5458 × 109 µm/RIU. We believe that this enhanced electric field together with the significantly improved GH shift would enable single molecular or even submolecular detection for hard-to-identify chemical and biological markers, including single nucleotide mismatch in the DNA sequence, toxic heavy metal ions, and tumor necrosis factor-α (TNFα).

Lead Halide Perovskite‐Based Dynamic Metasurfaces

AbstractLead halide perovskites CH3NH3PbX3 (MAPbX3) are known to have high refractive index and controllable bandgap, making them attractive for all‐dielectric and tunable metasurfaces. Till now, perovskite metasurfaces have only been used in structural colors. More interesting meta‐devices with 2π phase control are still absent. Here, MAPbX3‐perovskite‐based metasurfaces are experimentally demonstrated with a complete control of phase shift in a reflection mode. By utilizing MAPbBr3 cut‐wires as meta‐atoms on a ground metal film, it is found that the MAPbBr3 perovskite metasurface can produce full phase control from 0 to 2π and high reflection efficiency simultaneously. Consequently, high‐efficiency polarization conversion, anomalous reflection, and meta‐holograms are successfully produced. Most interestingly, the bandgap of the MAPbX3 perovskite can be post‐synthetically and reversibly tuned via anion exchange, providing a new approach to dynamically control of the all‐dielectric meta‐devices with novel function such as anomalous reflection and hologram.

Resonance-enhanced three-photon luminesce via lead halide perovskite metasurfaces for optical encoding

Lead halide perovskites have emerged as promising materials for photovoltaic and optoelectronic devices. However, their exceptional nonlinear properties have not been fully exploited in nanophotonics yet. Herein we fabricate methyl ammonium lead tri-bromide perovskite metasurfaces and explore their internal nonlinear processes. While both of third-order harmonic generation and three-photon luminescence are generated, the latter one is less affected by the material loss and has been significantly enhanced by a factor of 60. The corresponding simulation reveals that the improvement is caused by the resonant enhancement of incident laser. Interestingly, such kind of resonance-enhanced three-photon luminescence holds true for metasurfaces with a small period number of 4, enabling promising applications of perovskite metasurface in high-resolution nonlinear color nanoprinting and optical encoding. The encoded information ‘NANO’ is visible only when the incident laser is on-resonance. The off-resonance pumping and the single-photon excitation just produce a uniform dark or photoluminescence background.

Nanoimprinted perovskite metasurface for enhanced photoluminescence.

Recently, solution-processed hybrid halide perovskite has emerged as promising materials for advanced optoelectronic devices such as photovoltaics, photodetectors, light emitting diodes and lasers. In the mean time, all-dielectric metasurfaces with high-index materials have attracted attention due to their low-loss and high-efficient optical resonances. Because of its tunable by composition band gap in the visible frequencies, organolead halide perovskite could serve as a powerful platform for realizing high-index, low-loss metasurfaces. However, direct patterning of perovskite by lithography-based technique is not feasible due to material instability under moisture. Here we report novel organolead halide perovskite metasurfaces created by the cost-effective thermal nanoimprint technology. The nanoimprinted perovskite metasurface showed improved surface morphology and enhanced optical absorption properties. Significantly enhanced optical emission with an eight-fold enhancement in photoluminescence (PL) intensity was observed under room temperature. Temperature-dependent PL of perovskite nanograting metasurface was also investigated. Based on our results, we believe that thermal nanoimprint is a simple and cost-effective technique to fabricate perovskite-based metasurfaces, which could have broad impact on optoelectronic and photonic applications.

Organometallic Perovskite Metasurfaces.

Organometallic perovskites, solution-processable materials with outstanding optoelectronic properties and high index of refraction, provide a platform for all-dielectric metamaterials operating at visible frequencies. Perovskite metasurfaces with structural coloring tunable across visible frequencies are realized through subwavelength structuring. Moreover, a threefold increase of the luminescence yield and comparable reduction of luminescence decay time are observed.