Lead Halide Perovskite Single Crystals Research Articles

Recent progress of two‐dimensional lead halide perovskite single crystals: Crystal growth, physical properties, and device applications

AbstractIn recent years, research on organic‐inorganic lead halide two‐dimensional (2D) perovskites has been blossoming. 2D perovskites have completely different layered structures from three‐dimensional perovskites, with interleaved organic and inorganic layers, leading to 2D perovskite materials being more stable and possessing anisotropic electrical transport. Meanwhile, 2D organic‐inorganic lead halide perovskite single crystals are receiving increasing attention because of their remarkable properties, such as long charge carrier lifetime, low defect density, and high photoluminescence quantum yield, increasing their potential for optoelectronic applications. Previously, a series of material systems based 2D perovskites single crystals has been synthesized and applied in various device applications. In this review, the preparation methods of organic‐inorganic lead halide 2D perovskite single crystals, the growth principles, their photoelectric properties and several device applications are discussed.image

Ion Migrations in Lead Halide Perovskite Single Crystals with Different Halide Components

The ion migrations in lead halide perovskite (LHP)‐based devices are complex processes due to the generation of charges and migration multipaths. The migrating ions are generated mainly from element defects and dislocation defects, and transport along paths of element vacancies and grain boundaries. In this regard, it is of interest to investigate the different influences of the two defect types and paths. Herein, the current–voltage hysteresis and X‐ray photoelectron spectra of almost‐dislocation‐free LHP single crystals (LHPSCs) with different halide components are investigated. The ions cannot migrate in iodine‐based LHPSCs. A decrease in halide vacancy content in a bromine–chlorine‐based perovskite single crystal can effectively limit the ion migration. This study provides useful insights to understand the different dominant factors determining the ion migration in LHPs.

Microwave-Assisted Preparation of Organo-Lead Halide Perovskite Single Crystals.

The efficiency of organo-lead halide perovskite-based optoelectronic devices is dramatically lower for amorphous materials compared to highly crystalline ones. Therefore, it is challenging to optimize and scale up the production of large-sized single crystals of perovskite materials. Here, we describe a novel and original approach to preparing lead halide perovskite single crystals by applying microwave radiation during the crystallization. The microwave radiation primarily causes precise heating control in the whole volume and avoids temperature fluctuations. Moreover, this facile microwave-assisted method of preparation is highly reproducible and fully automated, it and can be applied for various different perovskite structures. In addition, this cost-effective method is expected to be easily scalable because of its versatility and low energy consumption. The crystallization process has low heat losses; therefore, only a low microwave reactor power of 8–15 W during the temperature changes and of less than 1 W during the temperature holding is needed.

High charge carrier mobility in solution processed one-dimensional lead halide perovskite single crystals and their application as photodetectors.

Organic inorganic hybrid metal halide perovskites have emerged as promising candidates for photovoltaics and light-emitting diodes. Recently, interest has been growing in the properties of low-dimensional metal halide perovskites, and one-dimensional versions with strong quantum confinement have demonstrated highly efficient broadband luminescence. Nevertheless, the charge transport mechanism in these low dimensional perovskites remains unclear. In this work, we characterised the charge mobility in one-dimensional perovskite single crystals using a space charge limited current method. Temperature dependent charge mobility measurements indicated that localized polarons at high temperature are replaced by delocalized polarons at low temperature with extended states in the polaronic band. A minimum mobility of 4.51 cm2 V-1 s-1 was measured at room temperature. UV photodetectors based on these crystals show an ultrahigh photoresponsivity of 132.3 A W-1. These findings show the promise of high mobility low dimensional perovskite materials for optoelectronic applications.

Photoluminescence enhancement and high accuracy patterning of lead halide perovskite single crystals by MeV ion beam irradiation

Using MeV ion irradiation, a PL enhancement effect of MAPbBr3 single crystals is demonstrated.

Bulk Organic-Inorganic Methylammonium Lead Halide Perovskite Single Crystals for Indirect Gamma Ray Detection.

Scintillators that convert ionization radiation photons to UV-visible photons have attracted extraordinary attention. Traditional scintillators are associated with a vacuum photomultiplier tube that faces strict constraints of fragility, magnetic fields, and operated voltage, or coupled to a silicon photomultiplier (SiPM) with optical silicone grease. Here, we report a high-performance radiation detector with an indirect photon-to-photon conversion radiation detection model based on perovskite single crystals (SCs), where perovskite SCs have been directly integrated into the window of SiPM by using the solution growth method at low temperature. Tunable X (γ)-ray excited light emission in the range of 414 to 600 nm is obtained with different concentrations of Br doping, which greatly matches the response wavelength of SiPM. Small Br-doped CH3NH3PbBr0.05Cl2.95 SCs exhibit high transmittance and weak self-absorption, resulting in improved scintillation light emissions. Moreover, we have successfully collected a 137Cs source gamma-ray pulse height spectrum with the SiPM readout. The MAPbBr0.05Cl2.95 scintillator exhibits a decay time of 0.14 ± 0.02 ns and a light yield of 18 000 photons/MeV with an energy resolution of 10.5 ± 0.4% at 662 keV. The results indicate that the CH3NH3PbBrxCl3-x perovskite SCs could enable the next generation of low-cost, fast, and fine-energy resolution scintillators.

Aqueous Synthesis of Low-Dimensional Lead Halide Perovskites for Room-Temperature Circularly Polarized Light Emission and Detection.

Low-dimensional lead halide perovskite materials are an emerging class of solution-processable semiconductors with promising potential applications in optoelectronic devices. Unfortunately, it is impossible to synthesize high-crystalline-quality low-dimensional perovskite single crystals without using chemotoxic solutions such as dimethylformamide/dimethyl sulfoxide or applying heating. Herein we report an economical and universal aqueous method to synthesize 2D layered and 1D chain perovskite single crystals at room temperature. The resultant chiral 2D perovskites can efficiently and selectively emit and detect circularly polarized light at room temperature. The as-synthesized 1D perovskite single crystals exhibit strong quantum confinement and enhanced self-trapped states that give efficient warm circularly polarized white-light emission. This aqueous synthetic method is general for other high-quality low-dimensional lead halide perovskite single crystals, and thus our findings would motivate more fundamental investigations on low-dimensional perovskites for potential optoelectronic applications.

Effects of Impurity Doping on Photoluminescence Properties of APbX3 Lead Halide Perovskites

The impact of introducing heterovalent Bi3+ impurities in APbX3 [A = CH3NH3, CH(NH2)2; X = I, Br] lead halide perovskite single crystals is investigated by means of photoluminescence (PL) spectroscopy. The element analysis reveals that Bi3+ ions are more easily incorporated into CH3NH3PbI3 than into the bromide perovskites CH(NH2)2PbBr3 and CH3NH3PbBr3. The three different halide perovskite single crystals used in this study exhibit a blueshift of the PL spectra at room temperature upon increasing the Bi3+ concentration. This blueshift is attributed to the weaker photon recycling effect that is induced by shorter PL lifetimes. The experiments reveal that the room‐temperature PL spectra of CH(NH2)2PbBr3 and CH3NH3PbI3 are relatively insensitive to impurity doping when compared to the PL spectrum obtained from CH3NH3PbBr3. On the other hand, doping with Bi3+ affects the low‐temperature PL properties of each sample in a different way, that is, its effect depends on the types of ions in the host material. The mechanism responsible for the shift of the PL spectra and the role of Bi3+ in lead halide perovskites are discussed.

Density of bulk trap states of hybrid lead halide perovskite single crystals: temperature modulated space-charge-limited-currents

Temperature-modulated space-charge-limited-current spectroscopy (TMSCLC) is applied to quantitatively evaluate the density of trap states in the band-gap with high energy resolution of semiconducting hybrid lead halide perovskite single crystals. Interestingly multicomponent deep trap states were observed in the pure perovskite crystals, which assumingly caused by the formation of nanodomains due to the presence of the mobile species in the perovskites.

Longitudinal Optical Phonons Modified by Organic Molecular Cation Motions in Organic-Inorganic Hybrid Perovskites.

We performed terahertz time-domain spectroscopy for methylammonium (MA) lead halide perovskite single crystals and characterized the longitudinal optical (LO) phonons directly. We found that the effective LO phonon wave number does not change in the wide temperature range between 10 and 300K. However, the coupling between MA cation modes and the LO phonon mode derived from lead halide cages induces a mode splitting at low temperatures and a damping of the LO phonon mode at high temperatures. These results influence the interpretation of electron-LO phonon interactions in perovskite semiconductors, as well as the interpretations of mobility, carrier diffusion, and polaron formation.

Understanding the Passivation Mechanisms and Opto-Electronic Spectral Response in Methylammonium Lead Halide Perovskite Single Crystals.

Attaining control over the surface traps in halide perovskites is critical for the tunability of ultimate device characteristics. Here, we present a study on the modulation of photophysical properties, surface traps, and recombination in MAPbI3 single crystals (MSCs) with methylamine (MA) vapor surface treatment. Transient photoluminescence spectroscopy in conjunction with density functional theory calculations reveals that nonradiative recombination related to Pb2+ becomes mitigated after MA vaporing while radiative recombination via bimolecular path tends to increase, which originates from the passivation of Pb ions with the Lewis base nitrogen in MA. In contrast to the broad photoresponse in the pristine MSC photodiodes, application of MA surface treatments leads to a spectral narrowing effect (SNE) in MSCs with the response peak width <40 nm. On the basis of the examined photon-cycling effect with MA treatment that indicates a reduction of exciton diffusion into the interior region of MSCs, we attempt to propose an operation mechanism for the SNE which can be related to the overall stronger surface recombination and resulting severe photocarrier losses, such that the charge collection and quantum efficiency from the above-band gap absorption decrease. This work provides a facile approach with chemical means to tune the surface properties and eventual spectral selectivity in MSCs that are promising for photon-detection device applications.

Understanding the temperature-dependent charge transport, structural variation and photoluminescent properties in methylammonium lead halide perovskite single crystals

Temperature dependent XRD illustrates a tetragonal to orthorhombic phase transition around 150 K in methylammonium lead halide perovskite single crystals.

Cs2AgInCl6 Double Perovskite Single Crystals: Parity Forbidden Transitions and Their Application For Sensitive and Fast UV Photodetectors

Double perovskite Cs2AgInCl6 is newly reported as a stable and environmentally friendly alternative to lead halide perovskites. However, the fundamental properties of this material remain unexplored. Here, we first produced high-quality Cs2AgInCl6 single crystals (SCs) with a low trap density of 8.6 × 108 cm–3, even lower than the value reported in the best lead halide perovskite SCs. Through systematical optical and electronic characterization, we experimentally verified the existence of the proposed parity-forbidden transition in Cs2AgInCl6 and identified the role of oxygen in controlling its optical properties. Furthermore, sensitive (dectivity of ∼1012 Jones), fast (3 dB bandwidth of 1035 Hz), and stable UV photodetectors were fabricated based on our Cs2AgInCl6 SCs, showcasing their advantages for optoelectronic applications.

Inorganic Lead Halide Perovskite Single Crystals: Phase‐Selective Low‐Temperature Growth, Carrier Transport Properties, and Self‐Powered Photodetection

Inorganic Lead Halide Perovskite Single Crystals: Phase‐Selective Low‐Temperature Growth, Carrier Transport Properties, and Self‐Powered Photodetection

X-ray Scintillation in Lead Halide Perovskite Crystals.

Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI3 and MAPbBr3 and two-dimensional (2D) (EDBE)PbCl4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications.