Hybrid perovskite thin films have demonstrated impressive performance for solar energy conversion and optoelectronic applications. However, further progress will benefit from a better knowledge of the intrinsic photophysics of materials. Here, the temperature-dependent emission properties of CHNHPbI single crystals are investigated and compared to those of thin polycrystalline films by means of steady-state and time-resolved photoluminescence spectroscopy. Single crystals photoluminescence present a sharp excitonic emission at high energy, with full width at half maximum of only 5 meV, assigned to free excitonic recombination. We highlight a strong thermal broadening of the free excitonic emission, due to exciton-LO-phonon coupling. The emission turned to be very short-lived with a subnanosecond dynamics, mainly induced by the fast trapping of the excitons. The free excitonic emission is completely absent of the thin film spectra, which are dominated by trap state bands.

Recently, Ruddlesden-Popper 2D perovskites (RPPs) solar cells and Light-Emitting Diodes (LED) have shown promising eciencies and improved stability in comparison to 3D halide perovskites. Here, the exciton recombination dynamics is investigated at room temperature in pure phase RPPs crystals (C 6 H 5 C 2 H 4 NH 3) 2 (CH 3 NH 3) n1 Pb n I 3n+1 (n=1, 2, 3 and 4) by time-resolved photoluminescence in a large range of power excitations. As the number of perovskite layers increases, we detect the presence of an increasing fraction of out-of-equilibrium free carriers just after photoexcitation, on a picosecond timescale, while the dynamics is characterized by the recombination of excitons with long lifetime spanning on several tens of nanoseconds. At low excitation power, the PL decays are non-exponential due to defect-assisted recombination. At high uence, defects are lled and many body interactions become important. Similarly to other 2D systems, Exciton-Exciton Annihilation (EEA) is then the dominant recombination path in a high density regime below the Mott transition.

Understanding the surface properties of organic-inorganic lead-based perovskites is of high importance to improve the device's performance. Here, we have investigated the differences between surface and bulk optical properties of CHNHPbBr single crystals. Depth-resolved cathodoluminescence was used to probe the near-surface region on a depth of a few microns. In addition, we have studied the transmitted luminescence through thicknesses between 50 and 600 μm. In both experiments, the expected spectral shift due to the reabsorption effect has been precisely calculated. We demonstrate that reabsorption explains the important variations reported for the emission energy of single crystals. Single crystals are partially transparent to their own luminescence, and radiative transport is the dominant mechanism for propagation of the excitation in thick crystals. The transmitted luminescence dynamics are characterized by a long rise time and a lengthening of their decay due to photon recycling and light trapping.

:During the past few years hybrid organic-inorganic perovskites (HOIPs) have attracted much interest as solution-processed semiconductors with high potentialities in optoelectronics and photovoltaics. On the one hand 3D HOIPs such as CH 3 NH 3 PbI 3 have shown their outstanding performances when incorporated in solar cells [1]. On the other hand their 2D layered counterparts such as (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 (PEPI) are promising materials for light emitting devices because of their strong emission at room temperature [2]. However, the optoelectronic properties of hybrid perovskite polycrystalline films suffer from a microscale grain structure. In order to take advantage of the great potential of these materials for both photovoltaïcs and emitting devices, the synthesis of large monocrystalline films is a key issue. Here we propose a fast crystallization method for the 2D layered hybrid perovskite PEPI. A vapor-assisted process coupled with a capping of the precursor solution allows to grow 2-dimensionnal thin films with millimetric monocrystalline grains, a high aspect ratio and a good surface quality (Fig.1). Moreover, this growth is several orders of magnitudes faster than the other reported techniques. In addition, we highlight the benefits of using γ-butyrolactone (GBL) for the growth of layered perovskites monocrystalline grains.

Due to their high potentiality for photovoltaic applications or coherent light sources, a renewed interest in hybrid organic perovskites has emerged for few years. When they are arranged in two dimensions, these materials can be considered as hybrid quantum wells. One consequence of the unique structure of 2D hybrid organic perovskites is a huge exciton binding energy that can be tailored through chemical engineering. We present experimental investigations of the exciton nonlinearities by means of femtosecond pump-probe spectroscopy. The exciton dynamics is fitted with a bi-exponential decay with a free exciton life-time of ∼100 ps. Moreover, an ultrafast intraband relaxation (< 150 fs) is also reported. Finally, the transient modification of the excitonic line is analyzed through the moment analysis and described in terms of reduction of the oscillator strength and linewidth broadening. We show that excitonic non-linearities in 2D hybrid organic perovskites share some behaviours of inorganic semiconductors despite their high exciton binding energy.

Exciton-polaritons, elementary excitations arising from the strong coupling regime between photons and excitons in insulators or semiconductors, represent a promising platform for studying quantum fluids of light and realizing prospective all-optical devices. Among different materials for room temperature polaritonic devices, twodimensional (2D) layered perovskites have recently emerged as one of the promising candidates thanks to their prominent excitonic features at room temperature. Here we report on the experimental demonstration of exciton-polaritons at room temperature in resonant metasurfaces made from a subwavelength 2D lattice of perovskite pillars. These metasurfaces are obtained via spincoating, followed by crystallization of the perovskite solution in a pre-patterned glass backbone. The strong coupling regime is revealed by both angular-resolved reflectivity and photoluminescence measurements, showing anticrossing between photonic modes and the exciton resonance with a Rabi splitting in the 200 meV range. Moreover, we show that the polaritonic dispersion can be engineered by tailoring the photonic Bloch mode to which perovskite excitons are coupled. Linear, parabolic, and multi-valley polaritonic dispersions are experimentally demonstrated. All of our results are perfectly reproduced by both numerical simulations based on a rigorous coupled wave analysis and an elementary model based on a quantum theory of radiation-matter interaction. Our results suggest a new approach to study exciton-polaritons and pave the way towards large-scale and low-cost integrated polaritonic devices operating at room temperature.

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Hybrid halide perovskites are now considered as key materials for contemporary research in photovoltaics and nanophotonics. In particular, because these materials can be solution processed, they represent a great hope for obtaining low cost devices. While the potential of 2D layered hybrid perovskites for polaritonic devices operating at room temperature has been demonstrated in the past, the potential of the 3D perovskites has been much less explored for this particular application. Here, we report the strong exciton-photon coupling with 3D bromide hybrid perovskite. Cavity polaritons are experimentallly demonstrated from both reflectivity and photoluminescence experiments, at room temperature, in a 3λ/2 planar microcavity containing a large surface spin-coated CH 3 NH 3 PbBr 3 thin film. A microcavity quality factor of 92 was found and a large Rabi splitting of 70 meV was measured. This result paves the way to low-cost polaritonic devices operating at room temperature, potentially electrically injectable as 3D hybrid perovskites present good transport properties.Cavity polaritons are half-light half-matter quasiparticles arising from the strong coupling regime between excitonic and photonic modes [1]. Such regime is achieved when the coupling strength, related to the oscillator strength quantifying the light-matter interaction in a material, is larger than the dissipation rates of uncoupled excitons and cavity photons. Thanks to its hybrid nature, cavity polaritons inherit the best features of both the excitonic and photonic component: strongly nonlinear bosonic particles which can propagate balistically over macroscopic distance, and can be injected/probed via optical means. These fascinating properties suggest not only a playground for studying physics of out of equilibrium Bose Einstein condensation, but also a potential platform for all-optical devices. In the later direction, many proof-of-concepts of polaritonic devices have been reported: polaritonic lasers [2], polariton transistors [3], resonant tunnelling diodes [4], interferometer [5], optical gates [3], and optical router [6]. Most of these demonstrations are in GaAs-based system the most accomplished technologies to engineer cavity polaritons. However, due to the small excitonic effects and oscillator strength in GaAs, their operating regime is limited to cryogenic temperature. For this reason, materials presenting strong excitonic effects at room temperature, such as the high band gap materials GaN [7,8] or ZnO [9, 10] are actively studied. However, the achievement of inorganic semiconductor engineered confined microstructures need sophisticated and high * emmanuelle.deleporte@ens-cachan.fr temperature epitaxial techniques. Looking for low-cost solutions, soft chemistry and low temperature processed materials presenting strong excitonic effects were also considered. The strong coupling regime at room temperature has been demonstrated in planar microcavities containing organic materials [11][12][13][14] or organic-inorganic halide perovskites such ...