Properties Of Hybrid Organic-inorganic Perovskites Research Articles

Tuning the Circular Dichroism and Circular Polarized Luminescence Intensities of Chiral 2D Hybrid Organic-Inorganic Perovskites through Halogenation of the Organic Ions.

Through the incorporation of various halogen-substituted chiral organic cations, the effects of chiral molecules on the chiroptical properties of hybrid organic-inorganic perovskites (HOIPs) are investigated. Among them, the HOIP having a Cl-substituted chiral cation exhibits the highest circular dichroism (CD) and circular polarized luminescence (CPL) intensities, indicating the existence of the largest rotatory strength, whereas the F-substituted HIOP shows the weakest intensities. The observed modulation can be correlated to the varied magnetic transition dipole of HOIPs, which is sensitive to the d-spacing between inorganic layers and the halogen-halogen interaction between organic cations and the inorganic sheets. These counteracting effects meet the optimal CD and CPL intensity with chlorine substitution, rendering the rotatory strength of HOIPs arranged in the order of (ClMBA)2 PbI4 >(BrMBA)2 PbI4 >(IMBA)2 PbI4 >(MBA)2 PbI4 >(FMBA)2 PbI4 .

Unraveling the Elastic Properties of (Quasi)Two-Dimensional Hybrid Perovskites: A Joint Experimental and Theoretical Study.

The unique properties of hybrid organic-inorganic perovskites (HOIPs) promise to open doors to next-generation flexible optoelectronic devices. Before such advances are realized, a fundamental understanding of the mechanical properties of HOIPs is required. Here, we combine ab initio density functional theory (DFT) modeling with a diverse set of experiments to study the elastic properties of (quasi)2D HOIPs. Specifically, we focus on (quasi)2D single crystals of phenethylammonium methylammonium lead iodide, (PEA)2PbI4(MAPbI3)n-1, and their 3D counterpart, MAPbI3. We used nanoindentation (both Hertzian and Oliver-Pharr analyses) in combination with elastic buckling instability experiments to establish the out-of-plane and in-plane elastic moduli. The effect of Van der Waals (vdW) forces, different interlayer interactions, and finite temperature are combined with DFT calculations to accurately model the system. Our results reveal a nonmonotonic dependence of both the in-plane and out-of plane elastic moduli on the number of inorganic layers (n) rationalized by first-principles calculations. We discuss how the presence of defects in as-grown crystals and macroscopic interlayer deformations affect the mechanical response of (quasi)2D HOIPs. Comparing the in- and out-of-plane experimental results with the theory reveals that perturbations to the covalent and ionic bonds (which hold a 2D layer together) is responsible for the relative out-of-plane stiffness of these materials. In contrast, we conjecture that the in-plane softness originates from macroscopic or mesoscopic motions between 2D layers during buckling experiments. Additionally, we learn how dispersion and π interactions in organic bilayers can have a determining role in the elastic response of the materials, especially in the out-of-plane direction. The understanding gained by comparing ab initio and experimental techniques paves the way for rational design of layered HOIPs with mechanical properties favorable for strain-intensive applications. Combined with filters for other favorable criteria, e.g., thermal or moisture stability, one can systematically screen viable (quasi)2D HOIPs for a variety of flexible optoelectronic applications.

Multi-Model Imaging of Local Chemistry and Ferroic Properties of Hybrid Organic-Inorganic Perovskites

Multi-Model Imaging of Local Chemistry and Ferroic Properties of Hybrid Organic-Inorganic Perovskites

Multiscale modeling of active layer of hybrid organic-inorganic solar cells for photovoltaic applications by means of density functional theory and integral equation theory of molecular liquids

Photovoltaic devices convert solar energy into electricity and are promising candidates to reduce carbon emission while providing an alternative way to meet increasing demand in energy consumption. In recent years, organic or hybrid organic-inorganic photovoltaic devices demonstrate steady increase in performance and stability and a promising tendency toward the low production cost. To make them attractive for commercial production, however, a deep understanding and ability to predict physical, chemical and electrochemical processes occurring in photovoltaic conversion layer is needed. Here, we present multiscale modeling of electronic and structural properties of hybrid organic-inorganic perovskites (OIP) of the type CH3NH3PbX3, X = Br, Cl, I, in contact with organic molecules of P3BT, P3HT, or SQ02, including adsorption on inorganic substrates of TiO2. Our methodology is based on Density Functional Theory (DFT) and integral equation theory of molecular liquids in the Reference Interaction Site Model (RISM). We apply it to study the photovoltaic thin film nanomorphology and determine the key factors affecting the performance of OIP-based bulk heterojunction solar cells through their influence on charge separation, charge transport and recombination losses in donor-acceptor blends. These factors include chemical composition of heterojunctions and mutual orientation of molecules on the border of the donor-acceptor or donor-acceptor-substrate systems. Since the formation of thin active layer of solar cells occurs in fluidic phase, we also provide a detailed microscopic insight into the organization of solvent molecules in the solvation shell structure and their contribution to the solvation thermodynamics. In total, these properties define charge transfer processes from donor to acceptor and are utilized in development of new generation organic and hybrid organic-inorganic solar cells. The calculated nanoscale morphologies serve as a guide in rational design of organic or hybrid photovoltaics.

Elastic Softness of Hybrid Lead Halide Perovskites.

Much recent attention has been devoted towards unraveling the microscopic optoelectronic properties of hybrid organic-inorganic perovskites. Here we investigate by coherent inelastic neutron scattering spectroscopy and Brillouin light scattering, low frequency acoustic phonons in four different hybrid perovskite single crystals: MAPbBr_{3}, FAPbBr_{3}, MAPbI_{3}, and α-FAPbI_{3} (MA: methylammonium, FA: formamidinium). We report a complete set of elastic constants characterized by a very soft shear modulus C_{44}. Further, a tendency towards an incipient ferroelastic transition is observed in FAPbBr_{3}. We observe a systematic lower sound group velocity in the technologically important iodide-based compounds compared to the bromide-based ones. The findings suggest that low thermal conductivity and hot phonon bottleneck phenomena are expected to be enhanced by low elastic stiffness, particularly in the case of the ultrasoft α-FAPbI_{3}.

Anomalous Growth and Coalescence Dynamics of Hybrid Perovskite Nanoparticles Observed by Liquid-Cell Transmission Electron Microscopy

We report on in situ observations of nucleation, growth, and aggregation of hybrid organic-inorganic perovskites by liquid-cell transmission electron microscopy. Direct crystallization of hybrid CH3NH3PbI3 nanoparticles is achieved through an electron beam-assisted solvent evaporation approach. Time-lapse liquid-cell TEM imaging of the nanoparticles reveals a growth trend which is not entirely consistent with the classical Lifshitz-Slyozov-Wagner growth model. Significantly complex dynamical behaviors are observed during the coalescence process of CH3NH3PbI3 nanoparticles. We propose that the chemical instability inherent in the hybrid perovskite iodides should be considered to understand this phenomenon in addition to the oriented attachment mechanism. This study provides a useful reference for understanding the intriguing chemical and physical properties of hybrid organic-inorganic perovskites.