ABSTRACT. The performance of hybrid organic perovskite (HOP) for solar energy conversion is driving a renewed interest in their light emitting properties. The recent observation of broad visible emission in layered HOP highlights their potential as white light emitters. Improvement of the efficiency of the material requires a better understanding of its photophysical properties. We present in-depth experimental investigations of white light (WL) emission in thin films of the (C6H11NH3)PbBr4. The broadband, strongly Stokes shifted emission presents a maximum at 90K when excited at 3.815 eV, and below this temperature coexists with an excitonic edge emission.X-rays and calorimetry measurements excludes the existence of a phase transition as an origin of the thermal behavior of the WL luminescence. The free excitonic emission quenches at low temperature, despite a binding energy estimated to 280 meV. Time-Resolved Photoluminescence spectroscopy reveals the multicomponent nature of the broad emission. We analyzed the dependence of these components as function of temperature and excitation energy. The results are consistent with the existence of self-trapped states. The quenching of the free exciton and the thermal evolution of the WL luminescence decay time are explained by the existence of an energy barrier against self-trapping, estimated to ~10 meV.

We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on twodimensional self-organized layers of (C6H5C2H4 − N H3)2P bI4 perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model. PACS numbers: Valid PACS appear hereOptical properties of soft materials have attracted much attention for years thanks to their potential applications in optoelectronics devices. In particular, these last years, an increasing number of studies are dedicated on hybrid organic-inorganic materials[1], due to the possibility of combining the properties both of inorganic materials (high mobility, electrical pumping, band engineering) and of organic materials (low cost technology, high luminescence quantum yield at room temperature). In this context, organic-inorganic perovkites, having a chemical formula (R − NH3) 2 MX 4 where R is an organic chain, M is a metal and X a halogen, represent a natural hybrid system. Such perovskites present a great flexibility in their optical properties: the spectral position of the excitonic transitions can be tailored by substituting different halides X [2, 3], the photoluminescence efficiency can be tailored by changing the organic part R [4]. This kind of perovskites has been studied both in the framework of fundamental studies [2,3,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] and of applications in optoelectronic as the active material in a distributed feedback laser for example [25]. Recently the strong coupling regime between the perovskite exciton and the optical mode of a Pérot-Fabry microcavity has been demonstrated at room temperature in the UV range [5] and in the visible range [6,7]. The physical properties of these new polaritons have now to be investigated. In particular, the demonstration of polariton-polariton interactions which lead to polariton scattering would be a breakthrough for the physics of these new devices in the context of the low threshold polariton lasers [26,27,28]. To evaluate these possibilities, a good knowledge of the perovskite material electronic properties is needed. As an example, the energy of the phonons and the strength of the electron-phonon coupling will indicate whether an efficient relaxation of perovskite polaritons is conceivable. Additionally, the origin of the different perosvkite luminescence lines has to be clarified to improve the knowledge about the exciton which couples to the cavity mode. .In this paper, we report on the optical properties of a particular perovskite molecule, namely [bi-(phenethylammonium) tetraiodoplumbate]: (C 6 H 5 C 2 H 4 − N H 3 ) 2 − P bI 4 (named PEPI), absorbing and emitting in the green part of the visible range. Photoluminescence (PL) ...

International audienceIn this review we examine recent theoretical investigations on 2D and 3D hybrid perovskites (HOP) that combine classical solid-state physics concepts and density functional theory (DFT) simulations as a tool for studying their optoelectronic properties. Such an approach allows one to define a new class of semiconductors, where the pseudocubic high temperature perovskite structure plays a central role. Bloch states and k.p Hamiltonians yield new insight into the influence of lattice distortions, including loss of inversion symmetry, as well as spin-orbit coupling. Electronic band folding and degeneracy, effective masses and optical absorption are analyzed. Concepts of Bloch and envelope functions, as well as confinement potential are discussed in the context of layered HOP and 3D HOP heterostructures. Screening and dielectric confinements are important for room temperature optical properties of 3D and layered HOP, respectively. Non-radiative Auger effects are analyzed for the first time close to the electronic band gap of 3D hybrid perovskites

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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.

We report on Pb,Br, N,H, C andH NMR experiments for studying the local order and dynamics in hybrid perovskite lattices. Pb NMR experiments conducted at room temperature on a series of MAPbX compounds (MA = CHNH; X = Cl, Br and I) showed that the isotropic Pb NMR shift is strongly dependent on the nature of the halogen ions. ThereforePb NMR appears to be a very promising tool for the characterisation of local order in mixed halogen hybrid perovskites. Pb NMR on MAPbBrI served as a proof of concept. Proton, C andN NMR experiments confirmed the results previously reported in the literature. Low temperature deuterium NMR measurements, down to 25 K, were carried out to investigate the structural phase transitions of MAPbBr. Spectral lineshapes allow following the successive phase transitions of MAPbBr. Finally, quadrupolar NMR lineshapes recorded in the orthorhombic phase were compared with simulated spectra, using DFT calculated electric field gradients (EFG). Computed data do not take into account any temperature effect. Thus, the discrepancy between the calculated and experimental EFG evidences the fact that MA cations are still subject to significant dynamics, even at 25 K.

We focus here our attention on a particular family of 2D-layered and 3D hybrid perovskite molecular crystals, the mixed perovskites (C6H5-C2H4-NH3)2PbZ4(1-x)Y4x and (CH3-NH3)PbZ3(1-x)Y3x, where Z and Y are halogen ions such as I, Br, and Cl. Studying experimentally the disorder-induced effects on the optical properties of the 2D mixed layered materials, we demonstrate that they can be considered as pseudobinary alloys, exactly like Ga1-xAlxAs, Cd1-xHgxTe inorganic semiconductors, or previously reported 3D mixed hybrid perovskite compounds. 2D-layered and 3D hybrid perovskites afford similar continuous optical tunability at room temperature. Our theoretical analysis allows one to describe the influence of alloying on the excitonic properties of 2D-layered perovskite molecular crystals. This model is further refined by considering different Bohr radii for pure compounds. This study confirms that despite a large binding energy of several 100 meV, the 2D excitons present a Wannier character rather than a Frenkel character. The small inhomogeneous broadening previously reported in 3D hybrid compounds at low temperature is similarly consistent with the Wannier character of free excitons.