Halide Perovskite Single Crystals Research Articles

Perovskite Single Crystals with Self‐Cleaning Surface for Efficient Photovoltaics

AbstractMetal halide perovskite single crystals are promising for diverse optoelectronic applications. As a universal issue of solution‐grown perovskite single crystals, surface contamination causes adverse effect on material properties and device performance. Herein, learning from the self‐cleaning effect of lotus leaf, we address the surface contamination issue by introducing an amphiphilic long‐chain organic amine into the perovskite crystal growth solution. Self‐assembly of CTAC provides a hydrophobic crystal surface, inducing spontaneous removal of residual growth solution, which results in clean surface and better optoelectronic properties of perovskite single crystals. An impressive efficiency of 23.4 % is obtained, setting a new record for FAxMA1‐xPbI3 single‐crystal perovskite solar cells (PSCs). Moreover, our strategy also applies to perovskite single crystals with different morphology and composition, which may contribute to improvement of other single‐crystal perovskite optoelectronic devices.

Perovskite Single Crystals with Self-Cleaning Surface for Efficient Photovoltaics.

Metal halide perovskite single crystals are promising for diverse optoelectronic applications. As a universal issue of solution-grown perovskite single crystals, surface contamination causes adverse effect on material properties and device performance. Herein, learning from the self-cleaning effect of lotus leaf, we address the surface contamination issue by introducing an amphiphilic long-chain organic amine into the perovskite crystal growth solution. Self-assembly of CTAC provides a hydrophobic crystal surface, inducing spontaneous removal of residual growth solution, which results in clean surface and better optoelectronic properties of perovskite single crystals. An impressive efficiency of 23.4 % is obtained, setting a new record for FAx MA1-x PbI3 single-crystal perovskite solar cells (PSCs). Moreover, our strategy also applies to perovskite single crystals with different morphology and composition, which may contribute to improvement of other single-crystal perovskite optoelectronic devices.

Crystallization kinetic engineering for growth of thin metal halide perovskite platelets

Thin Cs2AgBiBr6 platelets possessing optimized optical and photo-response properties are obtained via a crystallization kinetic regulation strategy.

Direct X-ray detectors made of zero-dimensional hybrid metal halide perovskite single crystals

A novel zero-dimensional cadmium hybrid metal halide (C19H18P)2CdCl4 single crystal was synthesized by inserting (C19H18P)+ into a [CdCl4]2− tetrahedron lattice through a slow volatilization method, which was proved to be a promising X-ray detector.

Footprints of scanning probe microscopy on halide perovskites.

Scanning probe microscopy (SPM) and advanced atomic force microscopy (AFM++) have become pivotal for nanoscale elucidation of the structural, optoelectronic and photovoltaic properties of halide perovskite single crystals and polycrystalline films, both under ex situ and in situ conditions. These techniques reveal detailed information about film topography, compositional mapping, charge distribution, near-field electrical behaviors, cation-lattice interactions, ion dynamics, piezoelectric characteristics, mechanical durability, thermal conductivity, and magnetic properties of doped perovskite lattices. This article outlines the advancements in SPM techniques that deepen our understanding of the optoelectronic and photovoltaic performances of halide perovskites.

Heterointerface Design of Perovskite Single Crystals for High-Performance X-Ray Imaging.

Metal halide perovskite single crystals (MHP-SCs) are known for their facile fabrication into large sizes using inexpensive solution methods. Owing to their combination of large mobility-lifetime products and strong X-ray absorption, they are considered promising materials for efficient X-ray detection. However, they suffer from large dark currents and severe ion migration, which limit their sensitivity and stability in critical X-ray detection applications. Herein, a heterointerface design is proposed to reduce both the dark current and ion migration by forming a heterojunction. In addition, the carrier transport performance is significantly improved using heterointerface engineering by designing a gradient band structure in the SCs. The SC heterojunction detectors exhibit a high sensitivity of 3.98 × 105 µC Gyair -1 cm-2 with a low detection limit of 12.2 nGyair s-1 and a high spatial resolution of 10.2 lp mm-1 during imaging. These values are among the highest reported for state-of-the-art MHP X-ray detectors. Moreover, the detectors show excellent stability under continuous X-ray irradiation and maintainclear X-ray imaging after 240 d. This study provides novel insights into the design and fabrication of X-ray detectors with high detection efficiency and stability, which are beneficial for developing inexpensive, high-resolution X-ray imaging equipment.

Integration of Large-Area Halide Perovskite Single Crystals and Substrates via Chemical Welding Using an Ionic Liquid for Applications in X-ray Detection.

The large carrier lifetime mobility product and strong stopping power for high-energy X-rays make halide perovskites an attractive candidate for next-generation X-ray detectors. In particular, high-energy X-rays in the range of several tens of keV require halide perovskite absorber layers with thicknesses exceeding a few millimeters. To avoid carrier scattering caused by grain boundaries at such thicknesses, the utilization of single crystals is desirable. Large-area single crystals are predominantly grown in a freestanding form, and integration onto a substrate is necessary for the fabrication of commercial devices. However, an effective method for integrating large single crystals onto a substrate has not yet been developed. In this study, a large-area (20 cm2) MAPbBr3 single crystal is bonded to an indium tin oxide (ITO) substrate using an ionic liquid, showing strong adhesion strength of 164 kPa. X-ray detectors based on ITO/MAPbBr3 single crystal bonded by methylammonium acetate achieved excellent sensitivity of 91,200 μC Gyair-1 cm-2, the highest among substrate-integrated halide perovskite single crystal X-ray detectors.

Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals (Small 48/2023)

Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals (Small 48/2023)

Promoting Band Splitting through Symmetry Breaking in Inorganic Halide Perovskite Single Crystals for High-Sensitivity X-ray Detection

Promoting Band Splitting through Symmetry Breaking in Inorganic Halide Perovskite Single Crystals for High-Sensitivity X-ray Detection

Surface and bulk contributions to electrical behavior of cesium lead bromide (CsPbBr3) single crystal

Halide perovskite single crystals (SCs) are becoming increasingly popular in the field of optoelectronics due to their superior properties compared to polycrystalline thin films. This is believed to be due to a lower concentration of defects in SCs. Research into the surface and bulk properties of SCs has been a focus area since their discovery. It can be challenging to investigate the surface and bulk properties of perovskite solar cells (PSCs) SCs. This study used impedance spectroscopy (IS) to differentiate between the surface and bulk electrical responses of cesium lead bromide (CsPbBr3) SCs, which is a technique that has been infrequently used in previous reports. This study examined the electrical response of CsPbBr3 solar cells (SCs) by measuring the Nyquist plots and capacitance-frequency responses under different optical excitations. The data collected under blue and red wavelengths were analyzed and compared, revealing that the photocurrent and capacitive response were stronger under blue light (λB) than under red light (λR). This systematic examination of the electrical response under different optical excitations has not been done before. This study observed that the low-frequency capacitance changes less under blue light than under red light. The reason for this difference is thought to be caused by the polarization of the interface between the metal contacts and the surface of the PSCs (SCs) or by the presence of defects in the SCs that affect conductivity. The rapid collection of carriers from the surface under λB means that they do not contribute to the increase in capacitance with temperature. As far as the authors are aware, investigations of the electrical responses of SCs, such as impedance and capacitance, under various illumination wavelengths and temperatures are uncommon in the bibliography.

Macroscopic Piezoelectricity of Halide Perovskite Single Crystals and Their Highly Sensitive Self-Powered X-ray Detectors.

The FAxMA1-xPbI3 single crystal has excellent semiconductor photoelectric performance and good stability; however, there have been conflicting opinions regarding its macroscopic piezoelectricity. Here, the FAxMA1-xPbI3 (x = 0-0.1) single crystals (FAx SCs) exhibit a high macroscopic piezoelectric d33 coefficient of over 10 pC/N. The single crystal transforms from a tetragonal ferroelectric phase to a cubic paraelectric phase at x = 0.1-0.125. Furthermore, the fully polarized MAPbI3 and FA0.05 SCs were applied to prepare self-powered X-ray detectors with vertical structures. The sensitivity of the detector reaches 5.1 × 104 μC·Gy-1·cm-2 under a 0 V bias voltage, and its detection limit is as low as 50 nGy/s. This work provides an approach to designing self-powered and high-quality detectors with piezoelectric semiconductors.

Room-temperature growth of perovskite single crystals via antisolvent-assisted confinement for high-performance electroluminescent devices

Organic-inorganic halide perovskite single crystals (OIHP-SCs) are promising light-emitting materials for bright electroluminescence (EL) devices due to their superior optoelectronic properties and excellent stability. However, the conventional high-temperature growth methods will inevitably disturb the ordered growth and introduce massive defects in OIHP-SCs, leading to the degradation of device performance. The preparation of thin OIHP-SCs with low trap-state densities for high-performance EL devices remains a formidable challenge. Here, we develop an efficient antisolvent-assisted confined growth (AACG) method for the room-temperature growth of formamidinium lead bromide (FAPbBr3) perovskite SCs. An antisolvent vapour environment is intentionally introduced in the spatially confined growth process to lower the free energy barrier for nucleation, enabling the growth of high-quality FAPbBr3 SCs at room temperature. Consequently, FAPbBr3 SCs with ultralow trap-state density of 2.15 × 109 cm−3 and amplified spontaneous emission (ASE) threshold of 7.1 µJ cm−2 could be achieved, representing the best results ever reported for FAPbBr3 SCs. By leveraging the high crystal quality of FAPbBr3 SCs, SC-based perovskite light-emitting diodes (PeLEDs) with a high luminance of over 26,000 cd m−2 and a peak current efficiency (CE) of 13.02 cd A−1 are demonstrated. Our work opens up new opportunities for the development of high-performance EL devices based on OIHP-SCs.

Interface Energy Alignment between Lead Halide Perovskite Single Crystals and TIPS-Pentacene.

At present, there is a huge development in optoelectronic applications using lead halide perovskites. Considering that device performance is largely governed by the transport of charges across interfaces and, therefore, the interfacial electronic structure, fundamental investigations of perovskite interfaces are highly necessary. In this study, we use high-resolution soft X-ray photoelectron spectroscopy based on synchrotron radiation to explore the interfacial energetics for the molecular layer of TIPS-pentacene and lead halide perovskite single crystals. We perform ultrahigh vacuum studies on multiple thicknesses of an in situ formed interface of TIPS-pentacene with four different in situ cleaved perovskite single crystals (MAPbI3, MAPbBr3, FAPbBr3, and CsxFA1-xPbBryI3-y). Our findings reveal a substantial shift of the TIPS-pentacene energy levels toward higher binding energies with increasing thickness, while the perovskite energy levels remain largely unaffected regardless of their composition. These shifts can be interpreted as band bending in the TIPS-pentacene, and such effects should be considered when assessing the energy alignment at perovskite/organic transport material interfaces. Furthermore, we were able to follow a reorganization on the MAPbI3 surface with the transformation of the surface C 1s into bulk C 1s.

Charge transport comparison of FA, MA and Cs lead halide perovskite single crystals for radiation detection

We report a systematic comparison of the charge transport and radiation detection properties of inorganic and organic metal bromide single crystal perovskites. We studied the performance of Bridgman-grown CsPbBr3 single crystals, together with solution-grown FAPbBr3 and MAPbBr3 single crystals. Laser time of flight is used to measure the drift mobilities for all samples, and we report a maxium mobility value of 121 ± 10 cm V−1 s−1 for CsPbBr3. Alpha particle measurements were used to assess the mobility-lifetime products, with values recorded in the range of 2 × 10−4 cm2 V−1 to 1 × 10−3 cm2 V−1. Low temperature measurements showed an increase in bulk resistivity at temperatures down to 260 K, but no significant change to the drift mobilities. The overall performance of the Cs, FA and MA samples is compared and their potential for use in gamma spectroscopy measurements is discussed.

Room-Temperature Solvent Evaporation Induced Crystallization: A General Strategy for Growth of Halide Perovskite Single Crystals by Applying the Le Chatelier's Principle.

The growth of high-quality halide perovskite single crystals is imperative to study their intrinsic physical properties and to realize high-performance optoelectronic devices. Here, a room-temperature solvent evaporation-induced crystallization (RTSEIC) method is reported based on Le Chatelier's principle, which provides a general strategy to grow halide perovskite single crystals including 3D, 2D, 1D, and 0D, and either hybrid or all-inorganic halide perovskites. Taking 2D n-BA2 PbBr4 (n-BA = butylammonium) as an example, the room-temperature crystallization kinetics is demonstrated. The centimeter-sized n-BA2 PbBr4 single crystals exhibit an extremely small full width at half maximum (FWHM) of 0.024° in (0 0 2) plane rocking curve and a small trap density of 2.74× 1010 cm-3 . The superior crystalline quality endows the n-BA2 PbBr4 single crystal ultraviolet photodetectors with recorded performance among reported n-BA2 PbBr4 ultraviolet photodetectors, demonstrating a detectivity reaching 1.8× 1013 Jones, a fast response time of 55 µs and a high on-off ratio of 104 . The low-cost, simple, general, and efficient RTSEIC method is anticipated to promote the blossoming of halide perovskites single crystals.

High-entropy halide perovskite single crystals stabilized by mild chemistry.

Although high-entropy materials are excellent candidates for a range of functional materials, their formation traditionally requires high-temperature synthetic procedures of over 1,000 °C and complex processing techniques such as hot rolling1-5. One route to address the extreme synthetic requirements for high-entropy materials should involve the design of crystal structures with ionic bonding networks and low cohesive energies. Here we develop room-temperature-solution (20 °C) and low-temperature-solution (80 °C) synthesis procedures for a new class of metal halide perovskite high-entropy semiconductor (HES) single crystals. Due to the soft, ionic lattice nature of metal halide perovskites, these HES single crystals are designed on the cubic Cs2MCl6 (M=Zr4+, Sn4+, Te4+, Hf4+, Re4+, Os4+, Ir4+ or Pt4+) vacancy-ordered double-perovskite structure from the self-assembly of stabilized complexes in multi-element inks, namely free Cs+ cations and five or six different isolated [MCl6]2- anionic octahedral molecules well-mixed in strong hydrochloric acid. The resulting single-phase single crystals span two HES families of five and six elements occupying the M-site as a random alloy in near-equimolar ratios, with the overall Cs2MCl6 crystal structure and stoichiometry maintained. The incorporation of various [MCl6]2- octahedral molecular orbitals disordered across high-entropy five- and six-element Cs2MCl6 single crystals produces complex vibrational and electronic structures with energy transfer interactions between the confined exciton states of the five or six different isolated octahedral molecules.

Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals.

Halide perovskites are ideal for next-generation optical devices and photovoltaics. Although perovskite single-crystals show reproducible optoelectronic properties, significant variations in the crystal size, anisotropy, density, defects, photoluminescence (PL), and carrier lifetime affect the sample properties and device performances. Homogenous size and shape FA/MAPbBr3 single microcrystals (MCs) with controlled edge lengths, crystal densities, PL lifetimes, and PL intensities are prepared by thermodynamically controlling and kinetically separating the crystal nucleation-growth processes using optimum N-cyclohexyl-2-pyrrolidone (CHP) concentration. The crystal growth kinetics at different CHP concentrations and temperatures are estimated spectroscopically by measuring the concentration of Pb (II). High-density cubic MCs with a homogenous size distribution, high PL intensities, and long PL lifetimes are obtained within minutes at high temperatures by the controlled addition of the pyrrolidone derivative. Conversely, the crystal size nonlinearly increases with time at low temperatures. The isotropically grown high-density single crystals at controlled nucleation-growth rates at 190°C with 20% CHP show the highest PL intensity and the longest PL lifetimes. This method offers thermodynamic and kinetic control of perovskite single-crystal growth with shape control.

Fabrication and Characterization of 2D Layered Perovskites with a Gradient Band Gap.

Vertical gradient band-gap heterostructures of two-dimensional (2D) layered perovskites have attracted considerable research interest due to their superior optoelectronic properties and demonstrated potential for use in optical devices. However, its fabrication has been challenging. In this investigation, 2D Ruddlesden-Popper mixed halide perovskite single crystals with a vertical gradient band gap were synthesized by using a solid-state halide diffusion process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements after diffusion confirm that the crystalline and morphology remain intact. The transmittance and photoluminescence (PL) spectra show the formation of a vertical gradient band gap that is ascribed to gradient halide distribution through halide intermixing. The mixed halide crystal exhibits high stability with completely suppressed phase segregation in the time-dependent PL measurement. The time-resolved photoluminescence (TRPL) spectra prove that the mixed halide sample has an enhanced carrier transport due to the Förster resonance energy transfer (FRET) effect. Besides, the halide diffusion behavior is found to be different from the previously proposed "layer-by-layer" diffusion model in exfoliated crystals. The gradient band-gap structure is critical for various applications in which vertical carrier transport is demanded.

Development of robust perovskite single crystal radiation detectors with high spectral resolution through synergetic trap deactivation and self‐healing

AbstractOrganic–inorganic halide perovskite single crystals (SCs) are promising materials for detecting ionizing radiation owing to their outstanding photoelectric conversion capability and inexpensive solution processability. However, the accuracy and stability of the detectors have been limited due to the charge traps and defects in SCs, especially when operated under high‐precision photon‐counting mode for energy spectrum acquisition. Here, we proposed a trap freezing deactivation route, which obviously suppressed dark current and noise by up to 97% and 92%, respectively. Furthermore, the bulk ion migration effect was essential for the ability to instantly self‐heal defects induced by radiation damage at temperatures down to −30°C. Consequently, the detector exhibits a record high energy resolution of 7.5% at 59.5 keV for 241Am γ‐ray source, which is the best solution‐processed semiconductor radiation detectors at the same energy range. In addition, the detector maintains over 90% of its initial performance after 9 months of storage when tested in the air. Our results will represent a revision of the paradigm that high‐spectral‐resolution and robust radiation detectors can only be realized with high temperature grown inorganic semiconductor single crystals.image

Enhancement of CsPbBr3 Perovskite Single-Crystal Photodetector Performance via Zr Ion Implantation

All-inorganic halide perovskite single crystals have attracted significant attention in optoelectronic fields on account of their outstanding optoelectronic properties. Photodetectors (PDs) based on CsPbBr3 single crystal exhibit high responsivity (R) and external quantum efficiency (EQE) due to the direct optical band gap, large optical absorption throughout the visible spectrum range, and long-term stability. Herein, we prepared the centimeter-size CsPbBr3 perovskite single crystal and utilized Zr ion implantation to modify the photoelectric properties of single crystals. The optical band gap of the CsPbBr3 single crystal decreases from 2.24 to 2.12 eV, and the absorption intensity increases after Zr ion implantation. The R and EQE of the CsPbBr3 single crystal photodetector modified by Zr ion implantation are 1.0 A W–1 and 294%, respectively, with a light intensity of 3.8 mW cm–2 and a 5 V bias under 425 nm illumination, which are ten times larger than that of the pristine devices. Meanwhile, the first-principles calculation results show that the introduction of Zr ions decreases the band gap and that the Zr 4d orbit contributes to the conduction band minimum (CBM), which facilitates carrier transport in Zr ion implanted CsPbBr3 single crystals. The results show that Zr ion implantation is an effective strategy to improve the performance of the CsPbBr3 single-crystal-based PDs.