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Mechanism of photoluminescence intermittency in organic-inorganic perovskite nanocrystals
摘要： Lead halide perovskite nanocrystals have demonstrated their potential as active materials for optoelectronic applications over the past few years. Nevertheless one issue which hampers their applicability has to do with the observation of photoluminescence intermittency, commonly referred to as blinking, as in their inorganic counterparts. Such behavior, reported for structures well above the quantum confinement regime, has been discussed to be strongly related with the presence of charge carrier traps. In this work we analyze the characteristics of this intermittency and explore the dependence with the surrounding atmosphere, showing evidence for the critical role played by the presence of oxygen. We discuss a possible mechanism in which a constant creation/annihilation of halide-related carrier traps takes place under light irradiation, the dominant rate being determined by the atmosphere.
关键词： photoluminescence,Hybrid organic inorganic perovskites,spectroscopy,nanocrystal,blinking
更新于2025-09-23 15:23:52
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Estimation of the Rashba Strength from Second Harmonic Generation in 2D and 3D Hybrid Organic-Inorganic Perovskites
摘要： The Rashba e?ect (RE), caused by concurrent spin-orbit coupling and structural inversion asymmetry (SIA), has been invoked to explain outstanding optoelectronic properties of hybrid organic inorganic perovskites (HOIPs). The SIA in HOIPs also manifests itself in second harmonic generation (SHG). Here we establish a quantitative relation between the RE strength and the low-frequency SHG value in 2D and 3D HOIPs using a newly developed e?ective-mass model. The calculated SHG, which exhibits one- and two-photon resonances between the valence and conduction bands, approaches a ?nite value at low frequencies. Using the measured SHG values in literature, the estimated RE strength is 10?3 eV?A for 3D CH3NH3PbI3 and 4 × 10?2 eV?A for 2D (C4H9NH3)2PbI4. Our results facilitate a simple and reliable determination of the RE strength of 2D and 3D HOIPs and help quantify the impact of RE on various properties in HOIPs.
关键词： second harmonic generation,Rashba effect,hybrid organic-inorganic perovskites,structural inversion asymmetry,spin-orbit coupling
更新于2025-09-23 15:21:01
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Kinetics of Ion-Exchange Reactions in Hybrid Organic-Inorganic Perovskite Thin Films Studied by In Situ Real-Time X-ray Scattering
摘要： The exchange of ions in hybrid organic-inorganic perovskites with the general formula APbX3 (A = MA, FA; X = I, Cl, Br) is studied in five different systems using in situ real-time grazing incident X-ray diffraction (GIXD). In systems where the organic cation is exchanged, we find a continuous shift of the lattice parameter. The relative shift compared to the pure materials is used to quantify the exchange. Whether or not a conversion is possible, as well as the amount of exchanged cations, depends on the halide used. In the case of the interconversion of MAPbI3 and MAPbCl3, we observe a decay of the diffraction peaks of the original perovskite and the emergence of new peaks corresponding to the structure with the alternative halide. Moreover, we determined the relevant time scales of the growth and decay of the perovskite structures.
关键词： ion-exchange reactions,kinetics,in situ real-time X-ray scattering,thin films,hybrid organic-inorganic perovskites
更新于2025-09-23 15:21:01
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Efficient and accurate calculation of band gaps of halide perovskites with the Tran-Blaha modified Becke-Johnson potential
摘要： We report on a reoptimization of the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential dedicated to the prediction of the band gaps of three-dimensional (3D) and layered hybrid organic-inorganic perovskites (HOPs) within pseudopotential-based density functional theory methods. These materials hold promise for future photovoltaic and optoelectronic applications. We begin by determining a set of parameters for 3D HOPs optimized over a large range of materials. Then we consider the case of layered HOPs. We design an empirical relationship that facilitates the prediction of band gaps of layered HOPs with arbitrary interlayer molecular spacers with a computational cost considerably lower than that of more advanced methods like hybrid functionals or GW. Our study also shows that substituting interlayer molecular chains of layered HOPs with Cs atoms is an appealing and cost-effective route to band gap calculations. Finally, we discuss the pitfalls and limitations of TB-mBJ for HOPs, notably its tendency to overestimate the effective masses due to the narrowing of the band dispersions. We expect our results to extend the use of TB-mBJ for other low-dimensional materials.
关键词： Tran-Blaha modified Becke-Johnson potential,halide perovskites,computational methods,band gaps,density functional theory,hybrid organic-inorganic perovskites,pseudopotential
更新于2025-09-19 17:15:36
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Magneto-electroluminescence response in 2D and 3D hybrid organica??inorganic perovskite light emitting diodes
摘要： We have studied the magneto-electroluminescence (MEL) response in light emitting diodes based on 2D-(PEA)2PbI4 and 3D-MAPbI3 hybrid organic–inorganic perovskites at cryogenic temperatures. We found that the MEL is negative, i.e., the EL decreases with the applied field strength, B. In addition, the MEL(B) response has a Lorentzian line shape whose width depends on the perovskite used. We interpret the MEL(B) response using the “Δg mechanism” in which the spin of the injected electron–hole (e–h) pairs oscillates between singlet and triplet configurations due to different precession frequencies of the electron and hole constituents that originate from the difference, Δg, in the electron and hole gyromagnetic constants, g. In this model, the MEL(B) linewidth is inversely proportional to the spin lifetime and Δg. The model used is validated by directly measuring the spin lifetime of photogenerated e–h pairs using the circularly polarized pump–probe transmission technique with 100 fs resolution.
关键词： hybrid organic–inorganic perovskites,spin lifetime,Δg mechanism,light emitting diodes,magneto-electroluminescence
更新于2025-09-19 17:13:59
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Heterogeneous Cationa??Lattice Interaction and Dynamics in Triple-Cation Perovskites Revealed by Infrared Vibrational Nanoscopy
摘要： Hybrid organic-inorganic perovskites exhibit extraordinary photovoltaic performance. This is believed to arise from almost liquid-like low-energy interactions among lattice ions and charge carriers. While spatial variations have recently been identified over multiple length scales in the optoelectronic responses, the relationship of the heterogeneity and the soft cation-lattice interactions has remained elusive. Here, we apply multivariate infrared vibrational nano-imaging to a formamidinium (FA)-methylammonium (MA)-cesium triple cation perovskite. By using the FA vibrational resonance as a probe of its local chemical environment, through spatial variation and correlation in composition, strength of cation-lattice coupling and its associated few-ps vibrational dynamics, we reveal how a varying local reaction field is correlated with the cation-lattice coupling. We attribute the associated heterogeneous lattice contraction to a non-uniform distribution of cesium cations. The observed varying elasticity of the lattice leads to disordered charge-phonon coupling and polaron formation, the control of which is central to improving perovskite photovoltaics.
关键词： charge-phonon coupling,infrared vibrational nano-imaging,Hybrid organic-inorganic perovskites,lattice contraction,photovoltaic performance,cation-lattice coupling,polaron formation,vibrational dynamics
更新于2025-09-19 17:13:59
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Preface: Two dimensional (2D) hybrid organic-inorganic perovskites
摘要： 2D hybrid organic-inorganic perovskites (HOIPs) have been intensively investigated over the past 30 years before the rise of photovoltaic 3D hybrid perovskites. Along with the increasing research interest on 2D materials, they have attracted much attention. On the one hand, 2D hybrid perovskites possess much improved photo- and chemical stability over their 3D counterparts. On the other hand, the delicate interplay of multiple atomic bonding forces in the crystal lattice enables them to exhibit extraordinary properties that traditional inorganic 2D materials are unable to show. More importantly, the chemical and structural diversity of 2D HOIPs offers greater opportunities to fine-tune and engineer properties and functionalities compared with their 3D counterparts.
关键词： chemical and structural diversity,atomic bonding forces,photo- and chemical stability,2D hybrid organic-inorganic perovskites,photovoltaic
更新于2025-09-09 09:28:46