Halide Perovskite Semiconductors Research Articles

CsPbBr3 perovskite detectors with 1.4% energy resolution for high-energy γ-rays

Halide perovskite semiconductors are poised to revitalize the field of ionizing radiation detection as they have done to solar photovoltaics. We show that all-inorganic perovskite CsPbBr3 devices resolve 137Cs 662-keV γ-rays with 1.4% energy resolution, as well as other X- and γ-rays with energies ranging from tens of keV to over 1 MeV in ambipolar sensing and unipolar hole-only sensing modes with crystal volumes of 6.65 mm3 and 297 mm3, respectively. We report the scale-up of CsPbBr3 ingots to up to 1.5 inches in diameter with an excellent hole mobility–lifetime product of 8 × 10−3 cm2 V−1 and a long hole lifetime of up to 296 μs. CsPbBr3 detectors demonstrate a wide temperature region from ~2 °C to ~70 °C for stable operation. Detectors protected with suitable encapsulants show a uniform response for over 18 months. Consequently, we identify perovskite CsPbBr3 semiconductor as an exceptional candidate for new-generation high-energy γ-ray detection. Energy resolution of high-energy photon detectors is desired for applications ranging from biomedical imaging to homeland security. In this work, perovskite-based γ-ray detection with 1.4% energy resolution is demonstrated.

Nonlinear optical properties of halide perovskites and their applications

Nonlinear optics has undergone dramatic developments in the past 60 years, which has revolutionized the photonic and optoelectronic fields with many essential applications such as electro-optic switching, frequency mixing, optical parametric oscillation, optical phase conjugation, and so forth. As one of the new and promising candidates for both next-generation photovoltaic and optoelectronic devices, halide perovskite semiconductors have attracted extensive research attention because of their excellent electrical and optical properties demonstrated in the linear optical regime. In the past five years, halide perovskites have become a new research frontier of nonlinear optical materials because their highly tunable chemical components and multiple structures provide a variety of outstanding nonlinear optical properties, which support a broad scope of nonlinear optical applications. In this review, we have summarized the nonlinear optical properties of halide perovskites categorized according to the second-, third-, and high-order processes. Aside from the more conventional nonlinear effects, such as sum and difference frequency generation, this review also pays attention to the lesser known but important nonlinear phenomena, such as linear and circular photogalvanic effects, the high-order shift current effect, and the multi-photon pumped photoluminescence. We have also reviewed and summarized the nonlinear applications of halide perovskites, including multi-photon pumped photoluminescence imaging, multi-photon pumped amplified spontaneous emission and lasing, sub-bandgap and self-powered photodetection, all-optical and electro-optic modulation, saturable absorption, optical limiting, and so on. It is our belief that halide perovskites have proven to be excellent candidates for promoting the upgrading and updating of nonlinear optical devices with greatly improved performance and novel functionalities.

Local Phonon Modes Concerned with the Self-Trapped Exciton State in CsPbBr3 Nanocrystals

The exciton–phonon coupling plays a significant role in the optical property of lead halide perovskite semiconductors, but the concerned phonon modes have not been well identified. Under the resona...

Golden hour for perovskite photonics

Halide perovskite semiconductors have emerged as promising candidates for the next-generation low-energy consumption, high-flexibility photonics and optoelectronic devices thanks to their superior optical and excitonic properties as well as fabrication convenience. This special issue, including three review papers and six original research papers, focuses on the studies of both fundamentals and applications of perovskite photonics, covering materials, excitonic properties, nonlinear optics, strong light–matter interactions, and optoelectronic devices.

Photoluminescence Excitation Spectroscopy of Defect‐Related States in MAPbI3 Perovskite Single Crystals

AbstractThe MAPbI3 halide perovskite single crystals are studied at 5 K temperature using the photoluminescence excitation spectroscopy. Two noninteracting types of states are determined: bound excitons and defect‐related states. Excitation of the crystal with light energy below the bound exciton resonance reveals the complex low‐density defect emission, otherwise hidden by the emission of bound excitons. A way to separate these defect‐related luminescence spectra is proposed, and the thorough study of this emission regime is carried out. The results of this study open an area of low‐density defect and dopant exploration in halide perovskite semiconductors.

Methylphosphonium Tin Bromide: A 3D Perovskite Molecular Ferroelectric Semiconductor.

3D ABX3 organic-inorganic halide perovskite (OIHP) semiconductors like [CH3 NH3 ]PbI3 have received great attention because of their various properties for wide applications. However, although a number of low-dimensional lead-based OIHP ferroelectric semiconductors have been documented, obtaining 3D ABX3 OIHP ferroelectric semiconductors is challenging. Herein, an A-site cation [CH3 PH3 ]+ (methylphosphonium, MP) is employed to successfully obtain a lead-free 3D ABX3 OIHP ferroelectric semiconductor MPSnBr3 , which shows clear above-room-temperature ferroelectricity and a direct bandgap of 2.62eV. It is emphasized that MPSnBr3 is a multiaxial molecular ferroelectric with the number of ferroelectric polar axes being as many as 12, which is far more than those of the other OIHP ferroelectric semiconductors and even the classical inorganic perovskite ferroelectric semiconductors BiFeO3 (4 polar axes) and BaTiO3 (3 polar axes). MPSnBr3 is the first MP-based 3D ABX3 OIHP ferroelectric semiconductor. This finding throws light on the exploration of other excellent 3D ABX3 OIHP ferroelectric semiconductors with great application prospects.

Manipulating Photon Propagation via a Perovskite Microwire Array

Manipulating the propagation of photons is meaningful for optical data recognition but extremely challenging. Recently, the metal halide perovskite semiconductors present great potential in photoni...

A solvent-based surface cleaning and passivation technique for suppressing ionic defects in high-mobility perovskite field-effect transistors

Organometal halide perovskite semiconductors could potentially be used to create field-effect transistors (FETs) with high carrier mobilities. However, the performance of these transistors is currently limited by the migration of ionic surface defects. Here, we show that a surface cleaning and passivation technique, which is based on a sequence of three solution-based steps, can reduce the concentration of ionic surface defects in halide-based perovskites without perturbing the crystal lattice. The approach consists of an initial cleaning step using a polar/nonpolar solvent, a healing step to remove surface organic halide vacancies and a second cleaning step. The surface treatment is shown to restore clean, near hysteresis-free transistor operation, even if the perovskite films are formed under non-optimized conditions, and can improve room-temperature FET mobility by two to three orders of magnitude compared to untreated films. Our methylammonium lead iodide (MAPbI3) FETs exhibit high n- and p-type mobilities of 3.0 cm2 V−1 s−1 and 1.8 cm2 V−1 s−1, respectively, at 300 K, and higher values (9.2 cm2 V−1 s−1; n-type) at 80 K. We also show that the approach can be used to transform PbI2 single crystals into high-quality, two-dimensional perovskite single crystals. A three-stage solution-based cleaning technique can increase the room-temperature mobility and reduce the hysteresis of organometal halide perovskite transistors by decreasing the surface defects in the perovskite films.

Elucidating the atomistic origin of anharmonicity in tetragonal CH3NH3PbI3 with Raman scattering

Halide perovskite (HP) semiconductors exhibit unique strong coupling between the electronic and structural dynamics. The high-temperature cubic phase of HPs is known to be entropically stabilized, with imaginary frequencies in the calculated phonon dispersion relation. Similar calculations, based on the static average crystal structure, predict a stable tetragonal phase with no imaginary modes. This work shows that in contrast to standard theory predictions, the room-temperature tetragonal phase of CH$_{3} $NH$_{3} $PbI$_{3}$ is strongly anharmonic. We use Raman polarization-orientation (PO) measurements and \textit{ab initio} molecular dynamics (AIMD) to investigate the origin and temperature evolution of the strong structural anharmonicity throughout the tetragonal phase. Raman PO measurements reveal a new spectral feature that resembles a soft mode. This mode shows an unusual continuous increase in damping with temperature which is indicative of an anharmonic potential surface. The analysis of AIMD trajectories identifies two major sources of anharmonicity: the orientational unlocking of the [CH$_{3} $NH$_{3}$]$^+$ ions and large amplitude octahedral tilting that continuously increases with temperature. Our work suggests that the standard phonon picture cannot describe the structural dynamics of tetragonal CH$_{3} $NH$_{3} $PbI$_{3}$.

Direct and indirect exciton transitions in two-dimensional lead halide perovskite semiconductors.

Atomically thin layers of two-dimensional lead halide perovskite semiconductors exhibit prominent light emission due to the inherently strong quantum and dielectric confinement. Electronic band structures and coupled electron-hole pairs (excitons), which govern the optical properties, are not well understood in these emergent two-dimensional materials. Here, we have performed both the steady-state and time-resolved photoluminescence spectroscopies with varying temperature to study the optical responses of a high-quality (PEA)2PbI4 single crystal. We observe a multitude of exciton transitions with different responses to temperature that suggests their different origins. Furthermore, our results suggest that the photoluminescence of layered perovskites is dominated by direct exciton transitions at low temperatures, while by an indirect exciton at high temperatures that can be explained by our proposed exciton band structure incorporating the interplay of Coulomb and Rashba effects. Our study sheds light on the intrinsic optical properties of two-dimensional perovskites that may be beneficial for the novel applications of perovskite-based devices.

Thermodynamic Stabilization of Mixed-Halide Perovskites against Phase Segregation

Mixing iodide and bromide in halide perovskite semiconductors is an effective strategy to tune their bandgap, therefore mixed-halide perovskites hold great promise for color-tunable LEDs and tandem solar cells. However, the bandgap of mixed-halide perovskites is unstable under (sun-)light, since the halides segregate into domains of different bandgaps. Using pressure-dependent ultrafast transient absorption spectroscopy, we show that high external pressure increases the range of thermodynamically stable halide mixing ratios. Chemical pressure, by inserting a smaller cation, has the same effect, which means that any iodide-to-bromide ratio can be thermodynamically stabilized by tuning the crystal volume and compressibility. We interpret this stabilization by an alteration of the Helmholtz free energy via the largely overlooked PdeltaV term.

Direct Band Gap Mixed-Valence Organic–inorganic Gold Perovskite as Visible Light Absorbers

Lead-free halide perovskite semiconductors are necessary due to the atmospheric instability and lead toxicity associated with the 3D lead halide perovskites. However, a stable lead-free perovskite ...

Thermoelectric properties of all-inorganic perovskite CsSnBr3: A combined experimental and theoretical study

Halide perovskite semiconductors have been actively considered for thermoelectric applications. We report the thermoelectric properties of thermally stable, all-inorganic perovskite CsSnBr3 prepared by two methods. Between 300 and 600 K, both types of CsSnBr3 crystals showed analogous trends of increasing Seebeck coefficients S and plummeting electrical conductivities σ. The counteraction between S and σ followed a semilogarithmic relation derived from a single band model for the electronic band structure of CsSnBr3. The ZT value maximized at ~0.01 and its enhancement by extrinsic doping is possible. Our results help assess the potential of CsSnBr3 and other halide perovskites as thermoelectric materials.

Efficient up-conversion photoluminescence in all-inorganic lead halide perovskite nanocrystals

Up-conversion photoluminescence (UCPL) refers to the elementary process where low-energy photons are converted into high-energy ones via consecutive interactions inside a medium. When additional energy is provided by internal thermal energy in the form of lattice vibrations (phonons), the process is called phonon-assisted UCPL. Here, we report the exceptionally large phonon-assisted energy gain of up to ~ 8kBT (kB is Boltzmann constant, T is temperature) on all-inorganic lead halide perovskite semiconductor colloidal nanocrystals that goes beyond the maximum capability of only harvesting optical phonon modes. By systematic optical study in combination with a statistical probability model, we explained the nontrivial phonon-assisted UCPL process in perovskites nanocrystals, where in addition to the strong electron-phonon (light-matter) coupling, other nonlinear processes such as phonon-phonon (matter-matter) interaction also effectively boost the up-conversion efficiency.

High sensitivity and rapid response ultraviolet photodetector of a tetragonal CsPbCl3 perovskite single crystal

Inorganic perovskite has attracted great interest due to its excellent optoelectronic properties. There are much less low band gap halide perovskite semiconductors, and CsPbCl3 is one of a wide band gap semiconductor in the perovskite family. In this study, a 0.5-mm CsPbCl3 perovskite single crystal with tetragonal structure and a direct band gap of 2.86 ± 0.3 eV is synthesized by flash evaporation of CsCl-PbCl2 solution. An ultraviolet photodetector based on a CsPbCl3 single crystal is fabricated, showing a photoresponse in a wide wavelength range of 280–435 nm, with a maximum responsivity of 0.272 A/W at 410 nm. Rise and decay response times of the device are less than 28.4 and 2.7 ms, respectively. The good performance of this CsPbCl3 photodetector indicates promising applications in the field of UV optoelectronic devices.

Emergence of Ferroelectricity in Halide Perovskites

AbstractPerovskite oxides such as PbZrxTi1−xO3 (PZT) and BaTiO3 show excellent dielectric, piezoelectric, pyroelectric, and ferroelectric properties simultaneously and have been widely used in capacitor, sensor, actuator, motor, surface acoustic wave devices, and energy storage applications. Recently, a variety of solution‐processed halide perovskite materials have been discovered to exhibit fascinating properties such as high charge mobility, strong light absorption, and even ferroelectricity. In this review, the recent progress on two classes of halide perovskite ferroelectrics is summarized. The first class is organo‐lead halide perovskite semiconductor such as MAPbI3 (MA=CH3NH3+), which is intensively pursued for solar cell and light emitting diode applications. Dynamic ferroelectric polarization is believed to be one of the essential factors to protect carriers from being scattered by charged defects in these halide perovskites. The second class is normal/multilayered halide perovskite ferroelectrics with large polarization or strong piezoelectricity. The piezoelectric coefficient of these latter perovskites can be as high as ≈1540 pC N−1, comparable to those of PZT‐based ferroelectrics. Multiaxial polarizations and morphotropic phase boundaries are also demonstrated in such halide perovskites. Overall, the fast development of halide perovskite ferroelectrics opens a new avenue for not only advancing fundamental materials science but also designing novel electronic and photoelectric devices.

Mechanisms of exceptional grain growth and stability in formamidinium lead triiodide thin films for perovskite solar cells

Pure formamidinium lead triiodide (α-FAPbI3) organic-inorganic halide perovskite (OIHP) semiconductor is very attractive for use as light absorber in the new thin-film perovskite solar cells (PSCs) technology. This is primarily because of its superior thermal stability, more suitable bandgap, and compositional simplicity. However, the existence of the photo-inactive non-perovskite δ-FAPbI3 polymorph (‘yellow’ phase) is a major hurdle in the path towards the development of α-FAPbI3-based PSCs. Also, there is general consensus that the fine-grained nature of OIHP thin films is detrimental to the environmental stability and performance of the resulting PSCs. In this context, here we take advantage of the polymorphism in FAPbI3, and use solvent-vapor-assisted δ-to-α phase transformation to induce exceptional grain coarsening (up to 50-fold) in 0.3-μm thickness FAPbI3 thin films, resulting in an unprecedented average grain size of up to ~9 μm. The underlying mechanisms are elucidated based on the results from a combination of some key experiments, which involve studying systematically the effects of time, temperature, initial grain size, and solvent polarity index (PI). The ultra-coarse-grained α-FAPbI3 thin films show dramatically improved environmental stability over their medium-grained counterparts, which is explained based on grain-boundary density arguments. PSCs made using the ultra-coarse-grained α-FAPbI3 thin films have improved photovoltaic (PV) performance, but it is somewhat modest. This is attributed to the underestimation of the effective grain size relevant to photocarrier dynamics.

Two-dimensional halide perovskite lateral epitaxial heterostructures.

Epitaxial heterostructures based on oxide perovskites and III-V, II-VI and transition metal dichalcogenide semiconductors form the foundation of modern electronics and optoelectronics1-7. Halide perovskites-an emerging family of tunable semiconductors with desirable properties-are attractive for applications such as solution-processed solar cells, light-emitting diodes, detectors and lasers8-15. Their inherently soft crystal lattice allows greater tolerance to lattice mismatch, making them promising for heterostructure formation and semiconductor integration16,17. Atomically sharp epitaxial interfaces are necessary to improve performance and fordevice miniaturization.However, epitaxial growth of atomically sharp heterostructures of halide perovskites has not yet been achieved, owing to their high intrinsic ion mobility, which leads to interdiffusion and large junction widths18-21, and owing to their poor chemical stability, which leads to decomposition of prior layers during the fabrication of subsequent layers. Therefore, understanding the origins of this instability and identifying effective approaches to suppress ion diffusion are of great importance22-26. Here we report an effective strategy to substantially inhibit in-plane ion diffusion in two-dimensional halide perovskites by incorporating rigid π-conjugated organic ligands. We demonstrate highly stable and tunable lateral epitaxial heterostructures, multiheterostructures and superlattices. Near-atomically sharp interfaces and epitaxial growth are revealed by low-dose aberration-corrected high-resolution transmission electron microscopy. Molecular dynamics simulations confirm the reduced heterostructure disorder and larger vacancy formation energies of the two-dimensional perovskites in the presence of conjugated ligands. These findings provide insights into the immobilization and stabilization of halide perovskite semiconductors and demonstrate a materials platform for complex and molecularly thin superlattices, devices and integrated circuits.

Enhanced Thermoelectric Performance in Lead-Free Inorganic CsSn1–xGexI3 Perovskite Semiconductors

Halide perovskite semiconductors exhibit ultralow thermal conductivities, making them potentially suitable for thermoelectric applications. Nevertheless, the thermoelectric properties of the protot...

Routes toward Long-Term Stability of Mixed-Halide Perovskites

In the recent anniversary issue of Trends in Chemistry, Brennan et al. review halide segregation in mixed-halide perovskites, discussing multiple perspectives on the underlying origins and reported routes to retard halide segregation. Here, we argue that only slowing down the segregation may be insufficient to achieve long-term stability.