Inorganic Lead Halide Perovskite Research Articles

Phonon Screening of Excitons in Semiconductors: Halide Perovskites and Beyond.

The abinitio Bethe-Salpeter equation (BSE) approach, an established method for the study of excitons in materials, is typically solved in a limit where only static screening from electrons is captured. Here, we generalize this framework to include dynamical screening from phonons at lowest order in the electron-phonon interaction. We apply this generalized BSE approach to a series of inorganic lead halide perovskites, CsPbX_{3}, with X=Cl, Br, and I. We find that inclusion of screening from phonons significantly reduces the computed exciton binding energies of these systems. By deriving a simple expression for phonon screening effects, we reveal general trends for their importance in semiconductors and insulators, based on a hydrogenic exciton model. We demonstrate that the magnitude of the phonon screening correction in isotropic materials can be reliably predicted using four material specific parameters: the reduced effective mass, static and optical dielectric constants, and frequency of the most strongly coupled longitudinal-optical phonon mode. This framework helps to elucidate the importance of phonon screening and its relation to excitonic properties in a broad class of semiconductors.

Green–white color switchable light-emitting devices based on laterally fused cesium lead bromide perovskite nanowires

Inorganic lead halide perovskites are excellent optoelectronic semiconductors; however, little has been known about the characteristics of their nanowire-based light-emitting devices (LEDs). We study the LEDs employing self-assembled CsPbBr3 nanowires as emission layers. They tend to form crystallographic orientation-consistent laterally fused parallel arrays when self-assembling into the emission layer in the device due to Coulomb attraction between such ionic semiconductors. At high nanowire concentration, the LED emits pure green light, and the carriers transport through Fowler–Nordheim (FN) quantum tunneling and direct injection successively. In contrast, at lower nanowire concentration, the luminescence of the LED shifts gradually from green to white with the increasing bias owing to participation of not only the nanowire layer but also the carrier transport layers in the carrier recombination processes. Meanwhile, its carrier transport experiences successively FN quantum tunneling, direct quantum tunneling, and direct injection with the increasing bias. These results highly improve our understanding of the characteristics of perovskite nanowires-based LEDs.

Unintentional passivation of 4-tertbutyl pyridine for improved efficiency and decreased operational stability of perovskite solar cells

Defect-induced nonradiative recombination limits power conversion efficiency (PCE) of organic–inorganic lead halide perovskite solar cells (PSCs). Recently, molecular passivation methods using ammonium salts and Lewis bases have been gathering tremendous attention for reducing defects at perovskite film surfaces. In this work, we find that an excess amount of 4-tert-butylpyridine (4-tBP), which is used as an additive for an organic hole transport layer, passivates surface defects of perovskite films and, therefore, improves the initial performance of PSCs. In PSCs with this 4-tBP passivation, we achieve very high open circuit voltages of >1.20 V, with a corresponding voltage deficit of 0.38 V, and PCEs of >20%. However, operational stability of PSCs under continuous illumination is greatly decreased. Thus, this work reveals that the 4-tBP passivation causes a trade-off between PCE and operational stability of PSCs.

Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite Nanocrystals.

The development of next-generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb–Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron–phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of time-resolved and temperature-dependent studies at Br K and Pb L3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temperature-dependent XAS results rules out thermal effects as the primary source of distortion of the Pb–Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr3 perovskites’ photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.

A Photoluminescent Lead Bromide Hybrid Perovskite Molecular Ferroelastic Semiconductor with Sequential High-Tc Phase Transitions.

Organic-inorganic hybrid lead halide perovskites have attracted great interest for their use in promising optoelectronic applications. However, reports of photoluminescent perovskite molecular ferroelastic semiconductors with sequential high-Tc phase transitions have been scarce. In this work, a one-dimensional lead bromide hybrid perovskite [N,N-dimethylethanolammonium]PbBr3 has been synthesized, undergoing high-Tc sequential phase transitions at around 351 and 444 K, higher than those of most previously discovered hybrid perovskite phase transition materials. The specific intermolecular hydrogen bond between cationic molecules provides the greatest contribution to its high Tc by increasing the barrier of molecular motion under the temperature stimuli. The prominent ferroelastic domain evolution is visually observed under orthogonally polarized light. In addition, [N,N-dimethylethanolammonium]PbBr3 exhibits semiconducting and orange light emission characteristics. This finding opens up an avenue for designing high-performance ferroelastic materials and provides great motivation for discovering new multifunctional materials for the next generation of smart devices.

Electron Beam Irradiation of Lead Halide Perovskite Solar Cells: Dedoping of Organic Hole Transport Materials despite Hardness of the Perovskite Layer.

Organic-inorganic lead halide perovskite solar cells (PSCs) are highly efficient, flexible, lightweight, and even tolerant to radiation, such as protons, electron beams (EB), and γ-rays, all of which makes them plausible candidates for use in space satellites and spacecrafts. However, the mechanisms of radiation damage of each component of PSC [an organic hole transport material (HTM), a perovskite layer, and an electron transport material (ETM)] are not yet fully understood. Herein, we investigated the EB irradiation effect (100 keV, up to 2.5 × 1015 cm-2) on binary-mixed A site cations and halide perovskite (MA0.13FA0.87PbI2.61Br0.39, MA:methylammonium cation and FA:formaminidium cation), a molecular HTM of doped SpiroOMeTAD, and an inorganic ETM of mesoporous TiO2. Despite the decreased power conversion efficiency of PSCs upon EB exposure, the photoconductivities of the perovskite, HTM, and ETM layers remained intact. In contrast, significant dedoping of HTM was observed, as confirmed by steady-state conductivity, photoabsorption, and X-ray photoelectron spectroscopy measurements. Notably, this damage could be healed by exposure to short-wavelength light, leading to a partial recovery of the PSC efficiency. Our work exemplifies the robustness of perovskite against EB and the degradation mechanism of the overall PSC performance.

Regulating the Film Growth and Reducing the Defects for Efficient CsPbIBr2 Solar Cells.

Inorganic lead halide perovskite CsPbIBr2 possesses good stability with a suitable band gap for tandem solar cells. Decreasing the defect concentration and improving the film quality is crucial to further increase the power conversion efficiency of CsPbIBr2 solar cells. Here, the crystallization dynamics of CsPbIBr2 films is regulated by introducing the volatile organic salt, formamidinium acetate (FAAc) into the precursor solution. It is found that FAAc slows the crystallization process of CsPbIBr2 films and pinhole-free films with large grains and smooth surfaces are obtained. The defect concentration of the films is decreased and the nonradiative recombination is significantly inhibited. By improving the film quality, the FAAc remarkably enhances the efficiency of CsPbIBr2 solar cells. The champion device delivers a power conversion efficiency of 9.44% and exhibits higher stability than the reference device. This finding provides an effective strategy for reducing defects, suppressing the recombination, and improving the performance of CsPbIBr2 solar cells.

Compositional Variation in Hybrid Organic–Inorganic Lead Halide Perovskites: Kinetically versus Thermodynamically Controlled Synthesis

Compositional Variation in Hybrid Organic–Inorganic Lead Halide Perovskites: Kinetically versus Thermodynamically Controlled Synthesis

Exploring the Structural Competition between the Black and the Yellow Phase of CsPbI3.

The realization of stable inorganic perovskites is crucial to enable low-cost solution-processed photovoltaics. However, the main candidate material, CsPbI3, suffers from a spontaneous phase transition at room temperature towards a photo-inactive orthorhombic δ-phase (yellow phase). Here we used theoretical and experimental methods to study the structural and electronic features that determine the stability of the CsPbI3 perovskite. We argued that the two physical characteristics that favor the black perovskite phase at low temperatures are the strong spatial confinement in nanocrystalline structures and the level of electron doping in the material. Within this context, we discussed practical procedures for the realization of long-lasting inorganic lead halide perovskites.

Tight-binding description of inorganic lead halide perovskites in cubic phase

Band structure of inorganic lead halide perovskites is substantially different from the band structure of group IV, III–V and II–VI semiconductors. However, the standard empirical tight-binding model with sp3d5s∗ basis gives nearly perfect fit of band structure calculated in the density functional theory. The tight-binding calculations of ultrathin CsPbI3 layer show good agreement with the corresponding DFT calculations. The parameters corrected for the experimental data allow for the numerically cheap atomistic calculations of inorganic perovskite nanostructures.

Water-Recycled Perovskite for White Light-Emitting Diodes

Organic–inorganic lead halide perovskites have attracted great interest because of their excellent optoelectronic property. The largest problem hindering the real application was degradation due to...

Modular Zwitterion-Functionalized Poly(isopropyl methacrylate) Polymers for Hosting Luminescent Lead Halide Perovskite Nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs) are an exciting class of luminescent materials with high defect tolerance and broad spectral tunability, but such NCs are vulnerable to degradati...

Temperature‐Gradient‐Controlled Method Enabling Shape Control of 2D Perovskite Single Crystals for Photodetection

2D hybrid organic–inorganic lead halide perovskites have been reported as promising photodetection active semiconductor materials due to their excellent photoelectric properties and stability. However, the solution growth of 2D crystal materials is affected adversely by narrow process windows, low process reproducibility, and small crystal sizes. Herein, a temperature‐gradient‐controlled method to grow high‐quality 2D perovskite crystals on the order of centimeters is developed. Using this new method, BA2PbI4 and mixed‐cation BA2FAxMA1−xPb2I7 crystals are produced with shape control and improved quality at the bottom of the precursor solution. Subsequently, their photoelectric responses are investigated comprehensively. Photodetectors based on these single crystals exhibit outstanding performances, affording 10−11 A dark current, > 103 on–off ratio, ≈10 mA W−1 responsivity, excellent stability, and linear photoresponse. Moreover, the annealing of crystals effectively reduces the dark current of the detectors. The mixed‐cation BA2FA0.4MA0.6Pb2I7 crystal demonstrates improved photoelectric response and a significant change in morphology.

CsPbBr3 Perovskite Nanocrystal: A Robust Photocatalyst for Realizing NO Abatement

Photocatalysis is a promising method for removing atmospheric NO but suffers from unsatisfactory removal efficiency and selectivity. Inorganic lead halide perovskites (LHPs) have been intensely investigated in the field of solar cells as new wonder materials. The intrinsic merits of LHPs provide additional opportunities for their use in fields beyond photovoltaics. Herein, for the first time, we extend the application of the low-cost lead inorganic CsPbBr3 perovskite to high-performance photocatalytic elimination of NO under visible-light irradiation. The CsPbBr3 nanocrystals (NCs) with an edge size of ca. 12 nm can reach a high NO removal activity (50.6%) under a gas hourly space velocity (GHSV) of 1,800,000 mL h–1 g–1 and obtain high selectivity (89.0%) for the formation of ionic species instead of more toxic NO2. A significant improvement for NO removal over the state-of-the-art photocatalysts with an outstanding long-term stability of up to 15 h is demonstrated. The excellent performance can be ascribed to the efficient charge separation and transfer and the visible-light-harvesting ability of CsPbBr3 NCs. These findings open a new avenue for the use of the low-cost, easy-to-process, highly efficient, and air-tolerant CsPbBr3 perovskites toward air pollution remediation.

Experimental Evidence of Chloride‐Induced Trap Passivation in Lead Halide Perovskites through Single Particle Blinking Studies

AbstractResearch into organic–inorganic lead halide perovskites as photoactive material in solar cells and other electro‐optical devices has made immense progress in recent years. However, efficiency losses resulting from deep traps associated with framework defects, still limit the performance of perovskite semiconductors. Defect passivation by the incorporation of dopants, such as chloride doping in methylammonium lead iodide (MAPbI3) perovskite, is stated as one of the most efficient ways to reduce trap densities. Commonly used parameters like improved photoluminescence (PL) quantum yields and extended PL lifetimes provide nonconclusive experimental evidence on trap density suppression by chloride doping. In this work, the effect of chloride doping on the crystal morphology, composition, and PL of MAPbI3 nanocrystals is carefully investigated. Besides the anticipated enhanced PL intensity and extended PL lifetime, single‐particle PL intermittency studies reveal brighter and longer ON‐states with increasing amounts of chloride doping, which represents additional evidence of effective chloride‐induced trap passivation. These findings provide important guidelines for generating lead halide perovskite materials with significantly reduced trap densities toward the fabrication of high‐performance optoelectronic devices.

Single-Step Microfluidic Synthesis of Halide Perovskite Nanolasers in Suspension

Chemically synthesized inorganic lead halide perovskite lasers based on nanostructures, generating coherent light at room temperature, and having a low threshold, have become powerful tools for var...

Interface engineering for high-efficiency perovskite solar cells

The power conversion efficiency of thin film solar cells using organic–inorganic hybrid lead halide perovskite as an absorber has achieved over 25%. An augment of the output voltage can further increase the efficiency approaching the Shockley–Queisser efficiency limitation, which is highly correlated with charge carrier management at interfaces in perovskite devices. This perspective presents some considerations to improve carrier transfer and reduce recombination loss for highly efficient perovskite solar cells, including primary requests on charge carrier transfer dynamics, reasonable design methodologies of interfacial materials, and tuning interface interaction between perovskite and charge transport layers.

Molecular Origin of the Asymmetric Photoluminescence Spectra of CsPbBr3 at Low Temperature.

CsPbBr3 has received wide attention due to its superior emission yield and better thermal stability compared to other organic-inorganic lead halide perovskites. In this study, through an interplay of theory and experiments, we investigate the molecular origin of the asymmetric low-temperature photoluminescence spectra of CsPbBr3. We conclude that the origin of this phenomenon lies in a local dipole moment (and the induced Stark effect) due to the preferential localization of Cs+ in either of two off-center positions of the empty space between the surrounding PbBr6 octahedra. With increasing temperature, Cs+ ions are gradually occupying positions closer and closer to the center of the cavities. The gradual loss of ordering in the Cs+ position with increasing temperature is the driving force for the formation of tetragonal-like arrangements within the orthorhombic lattice.

Design a novel multifunctional (CsPbBr3/Fe3O4)@MPSs@SiO2 magneto-optical microspheres for capturing circulating tumor cells

All inorganic lead halide perovskite nanocrystals with excellent photoelectric characteristics as one of attractive new photoelectric materials are capable to apply in a variety of optoelectronic devices, but their instability and toxicity strongly impedes biological application. Herein, a novel approach of combining physical loading with hydrolytic packaging was exploited to firstly implant CsPbBr3 nanocrystals (NCs) and Fe3O4 quantum dots (QDs) into the mesoporous polystyrene microspheres (MPSs), then a silica shell layer was further coated on it to form the stable, safe and non-toxic (CsPbBr3/Fe3O4)@MPSs@SiO2 magneto-optical microspheres. The double core-shells packaging way not only improves the stability of the magneto-optical microspheres, but also avoids direct contact between CsPbBr3 NCs and biological target such as circulating tumor cells (CTCs) to solve the problem of heavy metal Pb in such material system. These magneto-optical microspheres can capture CTCs from both breast cancer cells (MCF-7) and lung cancer patient's blood in a few minutes. This work created a simple, safe and one-step method to identify and capture CTCs, which opens a new chapter for the application of lead halide perovskite in the biological field.

Effect of Surface Ligands in Perovskite Nanocrystals: Extending in and Reaching out.

ConspectusThe rediscovery of the halide perovskite class of compounds and, in particular, the organic and inorganic lead halide perovskite (LHP) materials and lead-free derivatives has reached remarkable landmarks in numerous applications. First among these is the field of photovoltaics, which is at the core of today’s environmental sustainability efforts. Indeed, these efforts have born fruit, reaching to date a remarkable power conversion efficiency of 25.2% for a double-cation Cs, FA lead halide thin film device. Other applications include light and particle detectors as well as lighting. However, chemical and thermal degradation issues prevent perovskite-based devices and particularly photovoltaic modules from reaching the market. The soft ionic nature of LHPs makes these materials susceptible to delicate changes in the chemical environment. Therefore, control over their interface properties plays a critical role in maintaining their stability. Here we focus on LHP nanocrystals, where surface termination by ligands determines not only the stability of the material but also the crystallographic phase and crystal habit. A surface analysis of nanocrystal interfaces revealed the involvement of Brønsted type acid–base equilibrium in the modification of the ligand moieties present, which in turn can invoke dissolution and recrystallization into the more favorable phase in terms of minimization of the surface energy. A large library of surface ligands has already been developed showing both good chemical stability and good electronic surface passivation, resulting in near-unity emission quantum yields for some materials, particularly CsPbBr3. However, most of those ligands have a large organic tail hampering charge carrier transport and extraction in nanocrystal-based solid films.The unique perovskite structure that allows ligand substitution in the surface A (cation) sites and the soft ionic nature is expected to allow the accommodation of large dipoles across the perovskite crystal. This was shown to facilitate electron transfer across a molecular linked single-particle junction, creating a large built-in field across the junction nanodomains. This strategy could be useful for implementing LHP NCs in a p–n junction photovoltaic configuration as well as for a variety of electronic devices. A better understanding of the surface propeties of LHP nanocrystals will also enable better control of their growth on surfaces and in confined volumes, such as those afforded by metal–organic frameworks, zeolites, or chemically patterened surfaces such as anodic alumina, which have already been shown to significantly alter the properties of in-situ-grown LHP materials.