Taming Friedrich-Wintgen interference in resonant metasurface: vortex laser emitting at on-demand tilted-angle

Friedrich-Wintgen (FW) interference is an atypical coupling mechanism that grants loss exchange between leaky resonances in non-Hermitian classical and quantum systems. Intriguingly, such an mechanism makes it possible for destructive interference scenario in which a radiating wave becomes a bound state in the continuum (BIC) by giving away all of its losses. Here we propose and demonstrate experimentally an original concept to tailor FW-BICs as polarization singularity at on-demand wavevectors in optical metasurface. As a proof-of-concept, using hybrid organic-inorganic halide perovskite as active material, we empower this novel polarization singularity to obtain lasing emission exhibiting both highly directional emission at oblique angles and polarization vortex in momentum space. Our results pave the way to steerable coherent emission with tailored polarization pattern for applications in optical communication/manipulation in free-space, high-resolution imaging /focusing and data storage

Photoluminescence Tuning Through Irradiation Defects in CH3_3NH3_3PbI3_3 Perovskites

International audienceDefect engineering is applied to hybrid (CH3NH3)PbI3 organic–inorganic perovskites. These materials have become one of the most promising low‐cost alternatives to traditional semiconductors in the field of photovoltaics and light emitting devices. Here Helium ion irradiation at low energy has been used as a tool for the controlled introduction of point defects in both single crystals and polycrystalline thin films. The irradiation defects modify the opto‐electronic properties as probed using photoluminescence (PL) spectroscopy from 10 K to room‐temperature. Contrary to usual semiconductors, a very good resilience of the PL properties with irradiation is observed, even associated to an enhancement of the optical emission at low temperature. These results are discussed in relation with the tetragonal to orthorhombic low‐temperature phase transition below T = 160 K. A comparison between spectra from single crystals and polycrystalline films, both with and without irradiation defects, allows a better understanding of the light emission mechanisms in both kinds of samples. The authors thereby evidence radiation hardness of these materials and the specificity of defects and their impact on light emission properties

Using a confocal PL microscope to correlate the PL and structural properties of 2D-layered perovskites crystals and thin films

International audienceOver the past few years, hybrid organic perovskites (HOP) were found to be remarkable semiconductors with outstanding optoelectronics properties. These materials are very versatile, as their bandgap and the carrier confinement can be easily tuned chemically. Many studies have focused on 3D perovskites, that tend to be good absorbing materials for thin films photovoltaic devices. Alternatively, another class of perovskites, called 2D perovskites, is getting more attention. These 2D HOP have a natural quantum well structure and a high dielectric excitonic confinement. Nevertheless, many of the fundamental photophysics properties of these 2d HOP remain to be understood. In this presentation, we will study the photoluminescence properties of 2D perovskites based on phenylethylammonium (C6H5C2H4NH3)2PbI4 and their 2d/3d derivatives (including a proportion of methylammonium). A new method will be presented to grow large grains films as well as single crystals with large aspect ratios and low roughness [1]. These single crystals have a low proportion of defects and will be then used to unveil some of the intrinsic properties of these perovskites. In particular a cryogenic confocal study will be presented, to finely probe the optoelectronic properties (excitons/phonons, …) and the presence of defects in the produced samples

Exciton Cooling in 2D Perovskite Nanoplatelets: Rationalized Carrier-Induced Stark and Phonon Bottleneck Effects

International audienceUsing femtosecond transient absorption (fs-TA), we investigate the hot exciton relaxation dynamics in strongly confined lead iodide perovskite nanoplatelets (NPLs). The large quantum and dielectric confinement leads to discrete excitonic transitions and strong Stark features in the TA spectra. This prevents the use of conventional relaxation analysis methods extracting the carrier temperature or measuring the buildup of the band-edge bleaching. Instead, we show that the TA spectral line shape near the band-edge reflects the state of the system, which can be used to probe the exciton cooling dynamics. The ultrafast hot exciton relaxation in one- to three- monolayer-thick NPLs confirms the absence of intrinsic phonon bottleneck. However, excitation fluence-dependent measurements reveal a hot phonon bottleneck effect, which is found to be independent of the nature of the internal cations but strongly affected by the ligands and/or sample surface state. Together, these results suggest a role of the surface ligands in the cooling process

Exciton Cooling in 2D Perovskite Nanoplatelets: Rationalized exciton-induced Stark and Phonon Bottleneck Effects

International audienceHybrid halide perovskites have emerged as rising materials for solution-processed photovoltaics, photodetectors, and light-emitting devices. For these applications, a deep understanding of the relaxation mechanism within the photoactive material is crucial since the rate at which hot carriers relax to the band edge will directly impact the performance of the optoelectronic devices. Several groups have investigated the cooling process in hybrid perovskite bulk materials as thin films using pump-probe spectroscopy [1–3].More recently, the development of low dimensional perovskite structures has enabled the investigation of carrier cooling in confined materials. In these systems, slower cooling is expected even at low excitation density due to the larger energy level separation. An apparent intrinsic phonon bottleneck was observed in weakly confined nanocrystals (NCs) [4]. However, contradictory results were reported in strongly confined 2D perovskites: thin films and colloidal nanoplatelets (NPLs). [5,6] Thus, a clear understanding of the confinement effect in the ultrafast relaxation dynamics is lacking.Here, using fs transient absorption spectroscopy (TA), we investigate the cooling rate in lead iodide-based perovskite 2D nanostructures. For such strongly confined systems, we propose an alternative method to characterize the cooling process by analyzing the TA spectral lineshape evolution of the first excitonic transitions. Indeed, the strong Stark signals in the TA spectra and the discrete nature of the optical transitions prevent to use of the classical analysis model of relaxation by extracting the time-dependent carrier temperatures or measuring the build-up of the band state bleaching, as applied previously in bulk and bulk-like perovskites nanocrystals. Using global data analysis, we extracted the rates of carrier relaxation after pump excitation above the band edge, at low and high excitation density. The ultrafast hot exciton relaxation in one- and three-monolayer thick NPLs confirms the absence of intrinsic phonon bottleneck effect, which was found independent of the nature of the internals cations. Remarkably, we found an enhanced delayed cooling rate at higher carrier densities known as the hot phonon bottleneck effect, in the 2D layered perovskite thin films compared to colloidal n=1 NPLs. This fact suggested a role of the ligands y/o sample superficial state in the cooling process

Micro-photoluminescence study of halide perovskites monocrystalline films. Correlation between the structural and optoelectronics properties.

International audienceOver the past few years, organic inorganic halide perovskites were shown to present remarkable optoelectronic properties. A great attention has been paid to perovskites thin films, as an ideal building block for PV and LED devices. Despite many improvements, these thin films still possess a poly-crystalline structure, with micrometer grains and defects, that limit the efficiency of the devices.To avoid these structural issues, many efforts are dedicated to grow monocrystallines thin films. This poster will present an innovative growth technique that allows a simple and very fast growth of such perovskites films with good monocrystalline properties. This method is based on a “Anti solvent Vapor assisted Capping Crystallization” (AVCC). It has been easily adapted to various kind of perovskites: 2D (C6H5C2H4NH3)2PbI4, 3D (CH3NH3PbBr3), or 2D/3D mixes. In a second part of this poster, a cryogenic micro-photoluminescence study will be presented (with a sub micrometer precision). This technique allows to finely correlate the optoelectronic properties (excitons/phonons, …) of the produced films with their morphology. These properties are then compared to the one of spin coated polycrystalline perovskites films. This comparison is useful to extract the intrinsic properties of the perovskites crystals

2-dimensional hybrid perovskites activation with an organic luminophore for photovoltaic applications

International audienceThe excellent optical and electronic properties of hybrid organic-inorganic perovskites make them suitable active materials for optoelectronics devices. Here we focus the attention on the 2D lead halide hybrid perovskites having the general formula (RNH3)2PbX4. These self-assembled layered materials are particularly interesting for light emitting devices such as LEDs and Lasers. More recently, Smith et al have shown that 2D perovskites can be used as an active material in hybrid perovskite solar cells (PSCs) . Compared to 3D lead halide hybrid perovskites (RNH3)PbX3 these materials present a higher long-term stability, which is one of the main issue that hinders PSCs development in an industrial scale.A great advantage of 2D perovskites is their better chemical flexibility and tunability with respect to 3D perovskites. Here an adequately chosen luminophore has been introduced inside a lead bromide hybrid perovskite to improve light–harvesting and brilliance. The functionalized perovskite exhibits a much higher brilliance than the standard one, while respecting the 2D perovskite structure . The increase of the brilliance is due to an increase of the light-harvesting: the energy absorbed by the luminophore is transfered to the perovskite, and to a resonance effect between the Frenkel exciton of the luminophore and the Wannier exciton of the perovskite. Functionalizing the organic part of hybrid perovskites with adequate dyes in order to increase light harvesting can be a promising path to enhance PSCs performance

2-dimensional hybrid perovskites activation with an organic luminophore for photovoltaic applications

International audienceThe excellent optical and electronic properties of hybrid organic-inorganic perovskites make them suitable active materials for optoelectronics devices. Here we focus the attention on the 2D lead halide hybrid perovskites having the general formula (RNH3)2PbX4. These self-assembled layered materials are particularly interesting for light emitting devices such as LEDs and Lasers. More recently, Smith et al have shown that 2D perovskites can be used as an active material in hybrid perovskite solar cells (PSCs) . Compared to 3D lead halide hybrid perovskites (RNH3)PbX3 these materials present a higher long-term stability, which is one of the main issue that hinders PSCs development in an industrial scale.A great advantage of 2D perovskites is their better chemical flexibility and tunability with respect to 3D perovskites. Here an adequately chosen luminophore has been introduced inside a lead bromide hybrid perovskite to improve light–harvesting and brilliance. The functionalized perovskite exhibits a much higher brilliance than the standard one, while respecting the 2D perovskite structure . The increase of the brilliance is due to an increase of the light-harvesting: the energy absorbed by the luminophore is transfered to the perovskite, and to a resonance effect between the Frenkel exciton of the luminophore and the Wannier exciton of the perovskite. Functionalizing the organic part of hybrid perovskites with adequate dyes in order to increase light harvesting can be a promising path to enhance PSCs performance