120 mm single-crystalline perovskite and wafers: towards viable applications

Stable and Ultrasensitive X-Ray Detectors Based on Oriented Single-Crystal Perovskite Rods

Metal-halide perovskite single crystals (SCs) are promising candidates for next-generation X-ray detectors. X-ray detectors fabricated using perovskite FAPbI3 SCs exhibit high detection sensitivity. However, two pressing issues still need to be addressed for practical applications: the orientation-controlled growth and environmentally friendly acquisition of high-quality FAPbI3 SCs. In this study, large high-quality perovskite FAPbI3 SC rods (SCRs) with unique orientation are grown using a biomass-derived green solvent. Owing to the high carrier mobility and large bulk resistivity of the oriented FAPbI3 SCRs, the SC detectors realize a record high X-ray detection sensitivity (2.16 × 105 µC Gy-1 cm-2) and high sensitivity to dark current density ratio (1.93 × 109 Gy-1 s). Furthermore, the detectors exhibit both ultralow dark and X-ray current drifts, as well as a detection limit of 2 nGy s-1. These characteristics enable the detectors to achieve high-resolution X-ray imaging, even at dose rates as low as 12 nGy s-1. This study not only contributes a new technical solution for low-dose X-ray detection, but also establishes a new approach for the low-cost and environmentally friendly production of core materials for X-ray detectors.

Multidimensional high-throughput screening for mixed perovskite materials with machine learning

Mixed halide inorganic perovskites exhibit exceptional stability and photovoltaic performance and are considered to be promising photovoltaic materials. However, the chemical diversity of these materials presents a vast screening space, making it challenging to efficiently identify high-performance materials solely through theoretical calculations or experiments. To address this challenge, in this work, we introduce a multidimensional high-throughput screening strategy that combines machine learning with first-principles calculations, specifically designed to identify MHIPs with optimal bandgap and light absorption properties. The bandgap and light absorption models have achieved determination coefficients (r2) of 0.9896 and 0.9833, with root mean square errors of 0.1890 eV and 0.2190 105 eV · cm-1, respectively, demonstrating the high precision and reliability of the models. In the present work, the generation of 306 521 candidate materials through mixed B-site elements is reported, leading to the successful identification of 295 materials with ideal characteristics for MHIPs via screening. Subsequently, an in-depth density functional theory validation is conducted on 20 of these materials. The research results demonstrate that Cs2AgBi0.5Sb0.25Ir0.25I6 and CsSn0.75Ge0.25I3 exhibit outstanding performance, making them the most promising candidate materials for practical applications. These results fully confirm the scientific validity and effectiveness of our screening strategy, laying a solid foundation for the exploration and optimization of high-performance perovskite solar cell materials.

A high-performance X-ray detector based on large-size perovskite MAPbI3 single crystals grown by environmentally friendly solvents and advanced systems

In this paper, we report a novel hermetically sealed and precisely temperature-controlled growth system that grows MAPbI3 single crystals up to a size of 60 × 48 × 22 mm3. The grown crystals have lower defects and higher quality. It is expected to facilitate the commercialization of perovskite single crystals for optoelectronic applications.

The Perovskite Optoelectronic Devices - A Look at the Future

The perovskite materials are broadly incorporated into optoelectronic devices due to a number of advantages. Their rapid technological progress is related to the relatively simple fabrication process, low production cost and high efficiency. Significant improvement is made in the light emitting, detection performance and device design especially operating in the visible and near-infrared regions. This review presents the status and possible future development of the perovskite devices such as solar cells, photodetectors, and light-emitting diodes. The fundamental properties of perovskite materials related to their effective device applications are summarized. Since the development of the perovskite technology is mainly driven by the revolutionary evolution of the semiconductor perovskite solar cell as a robust candidate for next-generation solar energy harvesting, this topic is considered first. The device engineering of various perovskite photodetector structures, including perovskite quantum dot photodetectors, is then discussed in detail. Their performance is compared with the current commercial photodetectors available on the global market together with their challenges. Finally, the considerable progress in the fabrication of the perovskite light-emitting diodes with external quantum efficiency exceeding 20% is presented. The paper is completed in an attempt to determine the development of perovskite optoelectronic devices in the future.

Preparation Techniques for Perovskite Single Crystal Films: From Nucleation to Growth

Thickness-controllable perovskite single crystal films exhibit tremendous potential for various optoelectronic applications due to their capacity to leverage the relationship between diffusion length and absorption depth. However, the fabrication processes have suffered from difficulties in large-area production and poor quality with abundant surface defects. While post-treatments, such as passivation and polishing, can provide partial improvement in surface quality, the fundamental solution lies in the direct growth of high-quality single crystal films. In this work, we firstly summarize the basic principles of nucleation and growth phenomenon of crystalline materials. Advanced growth methods of perovskite single crystal films, including solution-based, vapor phase epitaxial growth, and top-down method, are discussed, highlighting their respective advantages and limitations. Finally, we also present future directions and the challenges that lie ahead in perovskite single crystal films.

Single-Crystal Perovskite for Solar Cell Applications

The advent of organic-inorganic hybrid metal halide perovskites has revolutionized photovoltaics, with polycrystalline thin films reaching over 26% efficiency and single-crystal perovskite solar cells (IC-PSCs) demonstrating ≈24%. However, research on single-crystal perovskites remains limited, leaving a crucial gap in optimizing solar energy conversion. Unlike polycrystalline films, which suffer from high defect densities and instability, single-crystal perovskites offer minimal defects, extended carrier lifetimes, and longer diffusion lengths, making them ideal for high-performance optoelectronics and essential for understanding perovskite material behavior. This review explores the advancements and potential of IC-PSCs, focusing on their superior efficiency, stability, and role in overcoming the limitations of polycrystalline counterparts. It covers device architecture, material composition, preparation methodologies, and recent breakthroughs, emphasizing the importance of further research to propel IC-PSCs toward commercial viability and future dominance in photovoltaic technology.

Space-Confined Growth for Thickness-Controlled Cs3Bi2I9 Perovskite Single Crystal Wafers for X-Ray Detectors

The Cs3Bi2I9 single crystal, as an all-inorganic non-lead perovskite, offers advantages such as stability and environmental friendliness. Its superior photoelectric properties, attributed to the absence of grain boundary influence, make it an outstanding X-ray detection material compared to polycrystals. In addition to material properties, X-ray detector performance is affected by the thickness of the absorption layer. Addressing this, a space-confined method is proposed. The temperature field is determined through finite element simulation, effectively guiding the design of the space-confined method. Through this innovative method, a series of thickness-controlled perovskite single crystal wafers (PSCWs) are successfully prepared. Corresponding X-ray detectors are then prepared, and the impact of single crystal thickness on device performance is investigated. With an increase in single crystal thickness, a rise followed by a decline in device sensitivity is observed, reaching an optimal value at 0.7 mm thickness at 40V mm-1 with a device performance of 11313.6µC Gy-1 cm-2. This space-confined method enables the direct growth of high-quality perovskite single crystals with specified thickness, eliminating the need for slicing or etching.

Real-time detection of aging status of methylammonium lead iodide perovskite thin films by using terahertz time-domain spectroscopy

The inadequate stability of organic-inorganic hybrid perovskites remains a significant barrier to their widespread commercial application in optoelectronic devices. Aging phenomena profoundly affect the optoelectronic performance of perovskite-based devices. In addition to enhancing perovskite stability, the real-time detection of aging status, aimed at monitoring the aging progression, holds paramount importance for both fundamental research and the commercialization of organic-inorganic hybrid perovskites. In this study, the aging status of perovskite was real-time investigated by using terahertz time-domain spectroscopy. Our analysis consistently revealed a gradual decline in the intensity of the absorption peak at 0.968 THz with increasing perovskite aging. Furthermore, a systematic discussion was conducted on the variations in intensity and position of the terahertz absorption peaks as the perovskite aged. These findings facilitate the real-time assessment of perovskite aging, providing a promising method to expedite the commercialization of perovskite-based optoelectronic devices.

Diffusion of Solute Atoms in an Evaporated Liquid Droplet

Controlling the evaporation of a solvent has made it possible to grow crystals, nanoparticles, and microparticles from liquid droplets. At the heart of this process is the evaporation-induced diffusion of solute atoms, causing the liquid solution of the solute atoms to be in a supersaturated state. In this work, we analyze the mass transport in a spherical liquid droplet, which experiences the loss or evaporation of the solvents across the droplet surface. Using a pseudo-steady-state method, two approximate solutions are derived for the moving boundary problem: one is a linear function of the square of radial variable with a constraint to the loss rate of the solvent, and the other is an exponential function of the square of radial variable without any constraint to the loss rate of the solvent. The numerical results obtained from both approximate solutions are in accord with the numerical results from the finite element method, validating the approximate solutions. The results reveal that a small evaporation/loss rate of the solvent is needed to maintain a relatively uniform distribution of solute atoms in a liquid droplet during the solvent evaporation/loss.

Perovskite single-crystal thin films: preparation, surface engineering, and application

Perovskite single-crystal thin films (SCTFs) have emerged as a significant research hotspot in the field of optoelectronic devices owing to their low defect state density, long carrier diffusion length, and high environmental stability. However, the large-area and high-throughput preparation of perovskite SCTFs is limited by significant challenges in terms of reducing surface defects and manufacturing high-performance devices. This review focuses on the advances in the development of perovskite SCTFs with a large area, controlled thickness, and high quality. First, we provide an in-depth analysis of the mechanism and key factors that affect the nucleation and crystallization process and then classify the methods of preparing perovskite SCTFs. Second, the research progress on surface engineering for perovskite SCTFs is introduced. Third, we summarize the applications of perovskite SCTFs in photovoltaics, photodetectors, light-emitting devices, artificial synapse and field-effect transistor. Finally, the development opportunities and challenges in commercializing perovskite SCTFs are discussed.

Modeling Monte Carlo simulation on photon regeneration effects of perovskite FAPbI3 for photovoltaic applications

Controlling the photon regeneration effects in FAPbI₃ films is a noteworthy approach to improve the photovoltaic (PV) efficiency of FAPbI₃-based solar cells. However, the lack of systematic study on the relationship between photon regeneration effects and PV efficiency in the experimental process makes it difficult to control the photon regeneration effects effectively. In this work, we combine the Monte Carlo sampling method and the polar coordinate calculation method to design a new algorithm for a detailed simulation of the main processes of photon regeneration effects affecting the PV efficiency in a model based on an n-i-p type FAPbI₃ perovskite solar cell (PSC). The algorithm is validated to be used to compare the power-conversion efficiency (PCE) of different PSCs to filter out the PSC structure with the highest PCE or to determine the range of material parameter values corresponding to the highest PCE. This work opens up new ideas to effectively control the photon regeneration effects in PSCs to improve the device PV efficiency.

Charge Carrier Recombination Dynamics in MAPb(BrxCl1-x)3 Single Crystals

Understanding carrier recombination processes in MAPb(Br_xCl_1-x)₃ crystals is essential for their photoelectrical applications. In this work, carrier recombination dynamics in MAPb(Br_xCl_1-x)₃ single crystals were studied by steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL), and time-resolved microwave photoconductivity (TRMC). By comparing TRPL and TRMC, we find TRPL of MAPb(Br_xCl_1-x)₃ (x < 0.98) single crystals is dominated by a hole trapping process while the long-lived component of TRMC is dominated by an electron trapping process. We also find both electron and hole trapping rates of MAPb(Br_xCl_1-x)₃ (x < 0.98) crystals decrease with an increase in Br content. A temperature-dependent PL study shows there are shallow trap states besides the deep level trap states in the MAPb(Br_0.82Cl_0.18)₃ crystal. The activation energy for holes in shallow trap states detrapped into the valence band is ∼0.1 eV, while the activation energy for free holes to be trapped into deep trap states is ∼0.4 eV. This work provides insight into carrier recombination processes in MAPb(Br_xCl_1-x)₃ single crystals.

Synthetic approaches for perovskite thin films and single-crystals

Halide perovskites are compelling candidates for the next generation of photovoltaic technologies owing to an unprecedented increase in power conversion efficiency and their low cost, facile fabrication and outstanding semiconductor properties.

Additive engineering with sodium azide material for efficient carbon-based perovskite solar cells

Electron transport layer surface modification approach to enhance overall performance of Carbon electrode based perovskite solar cell.

Halide Perovskite: A Promising Candidate for Next-Generation X-Ray Detectors

In the past decade, metal halide perovskite (HP) has become a superstar semiconductor material due to its great application potential in the photovoltaic and photoelectric fields. In fact, HP initially attracted worldwide attention because of its excellent photovoltaic efficiency. However, HP and its derivatives also show great promise in X-ray detection due to their strong X-ray absorption, high bulk resistivity, suitable optical bandgap, and compatibility with integrated circuits. In this review, the basic working principles and modes of both the direct-type and the indirect-type X-ray detectors are first summarized before discussing the applicability of HP for these two types of detection based on the pros and cons of different perovskites. Furthermore, the authors expand their view to different preparation methods developed for HP including single crystals and polycrystalline materials. Upon systematically analyzing their potential for X-ray detection and photoelectronic characteristics on the basis of different structures and dimensions (0D, 2D, and 3D), recent progress of HPs (mainly polycrystalline) applied to flexible X-ray detection are reviewed, and their practicability and feasibility are discussed. Finally, by reviewing the current research on HP-based X-ray detection, the challenges in this field are identified, and the main directions and prospects of future research are suggested.

Two-Dimensional Perovskite (PEA)2PbI4 Two-Color Blue-Green Photodetector

Perovskite materials have been widely used to fabricate solar cells, laser diodes and other photodevices, owing to the advantage of high absorption coefficient, long carrier life and shallow defect energy levels. However, due to easy hydrolysis, it is difficult to fabricate perovskite micro-nano devices. Herein, we developed a water-free device fabrication technology and fabricated a two-dimensional (C₆H₅C₂H₄NH₃)₂PbI₄ ((PEA)₂PbI₄) two-color blue-green light detector, which exhibits high detection performance under the illumination of two-color lasers (λ = 460 nm, 532 nm). Compared with bulk devices, the dark current of the fabricated devices (10⁻¹¹ A) was reduced by 2 orders of magnitude. The peak responsivity and detectivity are about 1 A/W and 10¹¹ Jones, respectively. The photodetection performance of the device is basically the same under the two-color lasers. Our results provide a new process to fabricate perovskite microelectronic devices, and the fabricated photodetector shows great application prospects in underwater detection, owing to the blue-green window existing in water.

Monocrystalline Methylammonium Lead Halide Perovskite Materials for Photovoltaics

Lead halide perovskite solar cells have been gaining more and more interest. In only a decade, huge research efforts from interdisciplinary communities enabled enormous scientific advances that rapidly led to energy conversion efficiency near that of record silicon solar cells, at an unprecedented pace. However, while for most materials the best solar cells were achieved with single crystals (SC), for perovskite the best cells have been so far achieved with polycrystalline (PC) thin films, despite the optoelectronic properties of perovskite SC are undoubtedly superior. Here, by taking as example monocrystalline methylammonium lead halide, the authors elaborate the literature from material synthesis and characterization to device fabrication and testing, to provide with plausible explanations for the relatively low efficiency, despite the superior optoelectronics performance. In particular, the authors focus on how solar cell performance is affected by anisotropy, crystal orientation, surface termination, interfaces, and device architecture. It is argued that, to unleash the full potential of monocrystalline perovskite, a holistic approach is needed in the design of next-generation device architecture. This would unquestionably lead to power conversion efficiency higher than those of PC perovskites and silicon solar cells, with tremendous impact on the swift deployment of renewable energy on a large scale.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Morphology and surface analyses for CH3NH3PbI3 perovskite thin films treated with versatile solvent-antisolvent vapors

Organometal halide perovskite (CH3NH3PbI3) semiconductors have been promising candidates as a photoactive layer for photovoltaics. Especially for high performance devices, the crystal structure and morphology of this perovskite layer should be optimized. In this experiment, by employing solvent-antisolvent vapor techniques during a modified sequential deposition of PbI2-CH3NH3I layers, the morphology engineering was carried out as a function of antisolvent species such as: chloroform, chlorobenzene, dichlorobenzene, toluene, and diethyl ether. Then, the optical, morphological, structural, and surface properties were characterized. When dimethyl sulfoxide (DMSO, solvent) and diethyl ether (antisolvent) vapors were employed, the CH3NH3PbI3 layer exhibited relatively desirable crystal structures and morphologies, resulting in an optical bandgap (E g) of 1.61 eV, crystallite size (t) of 89.5 nm, and high photoluminescence (PL) intensity. Finally, the stability of perovskite films toward water was found to be dependent on the morphologies with defects such as grain boundaries, which was evaluated through contact angle measurement.

Recent Advances in Perovskite Photodetectors for Image Sensing

In recent years, metal halide perovskites have been widely investigated to fabricate photodetectors for image sensing due to the excellent photoelectric performance, tunable bandgap, and low-cost solution preparation process. In this review, a comprehensive overview of the recent advances in perovskite photodetectors for image sensing is provided. First, the key performance parameters and the basic device types of photodetectors are briefly introduced. Then, the recent developments of image sensors on the basis of different dimensional perovskite materials, including 0D, 1D, 2D, and 3D perovskite materials, are highlighted. Besides the device structures and photoelectric properties of perovskite image sensors, the preparation methods of perovskite photodetector arrays are also analyzed. Subsequently, the single-pixel imaging of perovskite photodetectors and the strategies to fabricate narrowband perovskite photodetectors for color discrimination are discussed. Finally, the potential challenges and possible solutions for the future development of perovskite image sensors are presented.

Inch-sized high-quality perovskite single crystals by suppressing phase segregation for light-powered integrated circuits

The triple-cation mixed-halide perovskite (FA _x MA _y Cs_1-x-y )Pb(I_zBr_1-z )₃ (FAMACs) is the best composition for thin-film solar cells. Unfortunately, there is no effective method to prepare large single crystals (SCs) for more advanced applications. Here, we report an effective additive strategy to grow 2-inch-sized high-quality FAMACs SCs. It is found that the judiciously selected reductant [formic acid (FAH)] effectively minimizes iodide oxidation and cation deprotonation responsible for phase segregation. Consequently, the FAMACs SC shows more than fivefold enhancement in carrier lifetimes, high charge mobility, long carrier diffusion distance, as well as superior uniformity and long-term stability, making it possible for us to design high-performance self-powered integrated circuit photodetector. The device exhibits large responsivity, high photoconductive gain, excellent detectivity, and fast response speed; all values are among the highest reported to date for planar-type single-crystalline perovskite photodetectors. Furthermore, an integrated imaging system is fabricated on the basis of 12 × 12 pixelated matrixes of the single-crystal photodetectors.

Recent Progress in Growth of Single-Crystal Perovskites for Photovoltaic Applications

The growth of high-quality single-crystal (SC) perovskite films is a great strategy for the fabrication of defect-free perovskite solar cells (PSCs) with photovoltaic parameters close to the theoretical limit, which resulted in high efficiency and superior stability of the device. Plenty of growth methods for perovskite SCs are available to achieve a maximum power conversion efficiency (PCE) surpassing 21% for SC-based PSCs. However, there is still a lot of room to further push the efficiency by considering new crystal growth techniques, interface engineering, passivation approaches, and additive engineering. In this review, we summarize the recent progress in the growth of SC-based perovskite films for the fabrication of high-efficiency and stable PSCs. We describe the impact of SC growth of perovskite films and their quality on the device performance and stability, compared with the commonly used polycrystalline perovskite films. In the last section, the challenges and potential of SCs in PSCs are also covered for future development.

Room-temperature synthesis, growth mechanisms and opto-electronic properties of organic–inorganic halide perovskite CH3NH3PbX3 (X = I, Br, and Cl) single crystals

Growth of MAPbX₃ (X = I, Br, and Cl) single crystals by room temperature crystallization (RTC) method, and the crystallization pathway illustrated by the solubility curve of MAPbCl₃ in DMSO, compared with inverse temperature crystallization (ITC) method.

Electronic effects of nano-confinement in functional organic and inorganic materials for optoelectronics

This review provides a comprehensive overview of the electronic effects of nano-confinement (from 1D to 3D geometries) on optoelectronic materials and their applications.

Effects of ITO Substrate Hydrophobicity on Crystallization and Properties of MAPbBr3 Single-Crystal Thin Films

Fabricating perovskite single-crystal thin films (SCTFs) in controllable manner is the major challenge for the promising potential applications in optoelectronic devices. Although modifying the substrate surface is frequently used to realize the controlled growth of perovskite SCTFs, it is still unclear how the substrate condition affects the crystallization process. In this work, we systemically investigated the effects of the surface hydrophobicity of indium tin oxide substrates on the crystallization process of MAPbBr3 SCTFs prepared by the space-confined method. Comprehensive characterizations show that the surface morphology and crystallinity of SCTFs are improved, and the defect density is reduced when increasing the substrate hydrophobicity. The best MAPbBr3 thin film obtained has a full width at half-height of the rocking curve of the (001) crystal plane of 0.044°. The mechanism of the substrate hydrophobicity on the crystal growth is also discussed. These results will provide guidance to the controllable growth of high-quality SCTFs for perovskite SCTF devices.

Halide Perovskite Single Crystals: Optoelectronic Applications and Strategical Approaches

Halide perovskite is one of the most promising semiconducting materials in a variety of fields such as solar cells, photodetectors, and light-emitting diodes. Lead halide perovskite single crystals featuring long diffusion length, high carrier mobility, large light absorption coefficient and low defect density, have been attracting increasing attention. Fundamental study of the intrinsic nature keeps revealing the superior optoelectrical properties of perovskite single crystals over their polycrystalline thin film counterparts, but to date, the device performance lags behind. The best power conversion efficiency (PCE) of single crystal-based solar cells is 21.9%, falling behind that of polycrystalline thin film solar cells (25.2%). The oversized thickness, defective surfaces, and difficulties in depositing functional layers, hinder the application of halide perovskite single crystals in optoelectronic devices. Efforts have been made to synthesize large-area single crystalline thin films directly on conductive substrates and apply defect engineering approaches to improve the surface properties. This review starts from a comprehensive introduction of the optoelectrical properties of perovskite single crystals. Then, the synthesis methods for high-quality bulk crystals and single-crystalline thin films are introduced and compared, followed by a systematic review of their optoelectronic applications including solar cells, photodetectors, and X-ray detectors. The challenges and strategical approaches for high-performance applications are summarized at the end with a brief outlook on future work.

Reducing Detrimental Defects for High-Performance Metal Halide Perovskite Solar Cells

In several photovoltaic (PV) technologies, the presence of electronic defects within the semiconductor band gap limit the efficiency, reproducibility, as well as lifetime. Metal halide perovskites (MHPs) have drawn great attention because of their excellent photovoltaic properties that can be achieved even without a very strict film-growth control processing. Much has been done theoretically in describing the different point defects in MHPs. Herein, we discuss the experimental challenges in thoroughly characterizing the defects in MHPs such as, experimental assignment of the type of defects, defects densities, and the energy positions within the band gap induced by these defects. The second topic of this Review is passivation strategies. Based on a literature survey, the different types of defects that are important to consider and need to be minimized are examined. A complete fundamental understanding of defect nature in MHPs is needed to further improve their optoelectronic functionalities.

Room-temperature liquid diffused separation induced crystallization for high-quality perovskite single crystals

Large single crystals serve as an ideal platform for investigating intrinsic material properties and optoelectronic applications. Here we develop a method, namely, room-temperature liquid diffused separation induced crystallization that uses silicone oil to separate the solvent from the perovskite precursors, to grow high-quality perovskite single crystals. The growth kinetics of perovskite single crystals using this method is elucidated, and their structural and optoelectronic properties are carefully characterized. The resultant perovskite single crystals, taking CH₃NH₃PbBr₃ as an example, exhibit approximately 1 µs lifetime, a low trap density of 4.4 × 10⁹ cm⁻³, and high yield of 92%, which are appealing for visible light or X-ray detection. We hope our findings will be of great significance for the continued advancement of high-quality perovskite single crystals, through a better understanding of growth mechanisms and their deployment in various optoelectronics. The diffused separation induced crystallization strategy presents a major step forward for advancing the field on perovskite single crystals.

Perovskites are appealing for optoelectronics, but high-quality perovskite single crystals should be grown at low temperature to minimize trap density. Here, the authors report a room-temperature liquid-diffused-induced crystallization for growth of high-quality hybrid perovskite single crystals.

Single crystals of mixed Br/Cl and Sn-doped formamidinium lead halide perovskites via inverse temperature crystallization

Hybrid organic–inorganic perovskite mixed halides of FAPbBr_3−xCl_x and doped FAPb_1−xSn_xBr₃ were synthesized using a generalized inverse temperature crystallization (ITC) method. With an appropriate choice of solvents and crystallization temperatures we show that large millimeter sized single crystals of these hybrid perovskites can be grown in a matter of hours to days using ITC. The structural and optical properties of these single crystals were characterized systematically. The mixed metal and mixed halide perovskites displayed a compositional bandgap tuneability in the region of 2.05 eV to 2.57 eV. The electrical properties of the perovskite single crystals were determined using a space-charge limited current (SCLC) method. The trap density determined from SCLC was between 10⁹ and 10¹¹ cm⁻³ for all perovskites which is exceptionally low. The mobility was found to increase by one order of magnitude on the addition of only 3% Sn for FAPb_1−xSn_xBr₃ based perovskites which shows promise for enhancing the electrical properties. This demonstrates the generalizability of the ITC method to grow large high-quality perovskite single crystals with enhanced optical and electrical properties. In addition, it was observed for FAPbBr_3−xCl_x based perovskites that initially degraded surfaces with suppressed PL emission could be repaired by using an anti-solvent treatment re-enabling the PL emission. Other perovskite compounds did not display any degraded surfaces and exhibited excellent stability in ambient conditions.

FAPbBr_3−xCl_x and doped FAPb_1−xSn_xBr₃ perovskite single crystals were synthesized using inverse temperature crystallization (ITC). The single crystals displayed a bandgap tuneability of 2.05 eV to 2.57 eV and trap densities between 10⁹ to 10¹¹ cm⁻³.

Toward Highly Reproducible, Efficient, and Stable Perovskite Solar Cells via Interface Engineering with CoO Nanoplates

It is well-known that solution-processed polycrystalline perovskite films show a high density of parasitic traps and the defects mainly exist at grain boundaries and surfaces of polycrystal perovskite films, which would limit potential device performance by triggering the undesired recombination and impair device long-term stability by accelerating the degradation of perovskite films. In this regard, defect passivation is highly desirable for achieving efficient and stable perovskite solar cells (PSCs). Here, we report the fabrication of highly reproducible, efficient, and stable PSCs via interface engineering with CoO nanoplates. When a suitable concentration of CoO nanoplates solution is spin-coated on perovskite film, a discontinuous CoO nanoplates modified layer is obtained, which is advantageous to achieving highly photovoltaic performance of the device because the uncovered perovskite crystalline grains can guarantee the unobstructed transport of holes from perovskite layers to hole transport layers. Furthermore, the hydrophobic oleylamine ligands capped CoO nanoplates are well filled in the boundaries of perovskite crystalline grains to effectively passivate the trap states, suppress dark recombination, and enhance moisture-resistance. These benefits are propitious to achieving a 20.72% champion efficiency and a 20.20% steady-state efficiency of the devices with good reproducibility and stability.

Centimeter-scale 2D perovskite (PEA)2PbBr4 single crystal plates grown by a seeded solution method for photodetectors

Large-sized single-crystal two-dimensional (2D) perovskites are highly desirable owing to their fundamental properties and intriguing ability to boost devices. Herein, 2-phenylethylammonium lead bromide [(PEA)2PbBr4] single crystals, which are a violet-light-emitting 2D perovskite material, with typical lateral sizes of about one centimeter were successfully grown using a seeded solution method. The single-crystal plates showed a well-defined shape (rectangle or hexagon), a natural thickness (300-500 μm) similar to that of conventional silicon and InP wafers, a large aspect ratio of ∼20, and a smooth surface (root mean square, ∼0.7 nm). We integrated these single crystal plates into an ultraviolet photodetector, achieving a low dark current of ∼10-13 A and an efficient photoresponse (on/off ratio, ∼103). This experiment could easily be extended to grow freestanding 2D perovskite single crystals on a wafer scale for practical integrated optoelectronics.

Microconcave MAPbBr3 Single Crystal for High-Performance Photodetector

We present the first report of a new suspension method for obtaining cubic MAPbBr₃ single crystal with a concave surface. The cubic MAPbBr₃ crystal with microconcavity possesses good crystallinity and carrier lifetime. Excellent photoelectric performance was provided by the concavity-based MAPbBr₃ photodetectors because of the good light trapping and shortened carrier pathway. As a result, the concavity-based photodetector exhibits superior responsivity of 62.9 and 5.43 A W^-1 and EQE of 1.50 × 10⁴% and 1.30 × 10³% under low-power and high-power 520 nm irradiation of 3.67 μW cm^-2 and 35.4 mW cm^-2 at 3 V, respectively, which are more than 500% higher than those of the plane-based photodetector. In particular, the concavity-based photodetector has an ultrahigh detectivity of 6.5 × 10¹² Jones at ultralow power of 3.67 μW cm^-2, which is 6.5 times higher than that of the planar device.

Multi-inch single-crystalline perovskite membrane for high-detectivity flexible photosensors

Single crystalline perovskites exhibit high optical absorption, long carrier lifetime, large carrier mobility, low trap-state-density and high defect tolerance. Unfortunately, all single crystalline perovskites attained so far are limited to bulk single crystals and small area wafers. As such, it is impossible to design highly demanded flexible single-crystalline electronics and wearable devices including displays, touch sensing devices, transistors, etc. Herein we report a method of induced peripheral crystallization to prepare large area flexible single-crystalline membrane (SCM) of phenylethylamine lead iodide (C₆H₅C₂H₄NH₃)₂PbI₄ with area exceeding 2500 mm² and thinness as little as 0.6 μm. The ultrathin flexible SCM exhibits ultralow defect density, superior uniformity and long-term stability. Using the superior ultrathin membrane, a series of flexible photosensors were designed and fabricated to exhibit very high external quantum efficiency of 26530%, responsivity of 98.17 A W⁻¹ and detectivity as much as 1.62 × 10¹⁵ cm Hz^1/2 W⁻¹ (Jones).

Hybrid halide perovskite single crystals show excellent optoelectronic properties but their small size and large thickness limit their application. Herein Liu et al. grow large area ultrathin flexible crystalline membrane of layered perovskite and demonstrate high detectivity in the flexible photosensors.

The Role of Surface Defects in Photoluminescence and Decay Dynamics of High-Quality Perovskite MAPbI3 Single Crystals

Halide perovskites have recently been a star semiconductor material in photovoltaic field owing to their excellent optoelectronic properties. An in-depth understanding of the photoluminescence and carrier diffusion in these materials may facilitate the implementation of high-performance optolelctronic devices. Here, we report an unusual photoluminescence quenching phenomenon in MAPbI₃ single crystals. Interestingly, MAPbI₃ single crystal with higher crystalline quality shows a lower photoluminescence emission and a shorter decay time, indicating the surface imperfection plays an important role to the photoluminescence. The quick quenching process is attributed to the synergistic effect of localized effect at the defects and rapid inward diffusion.

A 1300 mm2 Ultrahigh-Performance Digital Imaging Assembly using High-Quality Perovskite Single Crystals

By fine-tuning the crystal nucleation and growth process, a low-temperature-gradient crystallization method is developed to fabricate high-quality perovskite CH3 NH3 PbBr3 single crystals with high carrier mobility of 81 ± 5 cm2 V-1 s-1 (>3 times larger than their thin film counterpart), long carrier lifetime of 899 ± 127 ns (>5 times larger than their thin film counterpart), and ultralow trap state density of 6.2 ± 2.7 × 109 cm-3 (even four orders of magnitude lower than that of single-crystalline silicon wafers). In fact, they are better than perovskite single crystals reported in prior work: their application in photosensors gives superior detectivity as high as 6 × 1013 Jones, ≈10-100 times better than commercial sensors made of silicon and InGaAs. Meanwhile, the response speed is as fast as 40 µs, ≈3 orders of magnitude faster than their thin film devices. A large-area (≈1300 mm2 ) imaging assembly composed of a 729-pixel sensor array is further designed and constructed, showing excellent imaging capability thanks to its superior quality and uniformity. This opens a new possibility to use the high-quality perovskite single-crystal-based devices for more advanced imaging sensors.

Phase Transition Control for High Performance Ruddlesden-Popper Perovskite Solar Cells

Ruddlesden-Popper reduced-dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template-induced nucleation and growth of the desired (BA)₂ (MA)₃ Pb₄ I₁₃ phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI₂ crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA)₂ (MA)₃ Pb₄ I₁₃ films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden-Popper perovskite structure and further improve optoelectronic and solar cell devices.

Design Growth of MAPbI3 Single Crystal with (220) Facets Exposed and Its Superior Optoelectronic Properties

MAPbI₃ is deemed as the most prominent member in hybrid perovskites family because of its extremely optoelectronic properties. However, some issues and puzzles are still in expectation of their answers, such as stabilities, hysteresis, ferroelectricity, and so on. To bridge the distinctions between MAPbI₃ single crystal and thin films, large-size single crystals are demanded. On the contrary, crystal structure anisotropy-dependent optoelectronic properties is an inevitable topic. A series of large-size MAPbI₃ single crystals with (220) facets exposed were successfully grown, using high concentration solutions and large-size seed crystals to match growth rates of (100) and (220) facets. The optoelectronic properties of photocurrents, responsivity, EQE, and detectivity clearly showed significant anisotropy of optoelectronic properties in MAPbI₃ single crystal. According to ion migration theory, the anisotropy of optoelectronic properties was interpreted. We hope this result will be helpful to guide oriented growth MAPbI₃ thin films.

Surface potential mapping and n-type conductivity in organic–inorganic lead iodide crystals

We demonstrated the electronic structure of CH₃NH₃PbI₃ and its variation on the surface via surface potential and work function distribution.

Crystallization of CH3NH3PbI3−xBrx perovskite from micro-droplets of lead acetate precursor solution

The crystallization of perovskite from a lead acetate precursor solution added with some PbBr₂ by a micro-droplet method is investigated.

Recent Progress in Single-Crystalline Perovskite Research Including Crystal Preparation, Property Evaluation, and Applications

Organic-inorganic lead halide perovskites are promising optoelectronic materials resulting from their significant light absorption properties and unique long carrier dynamics, such as a long carrier lifetime, carrier diffusion length, and high carrier mobility. These advantageous properties have allowed for the utilization of lead halide perovskite materials in solar cells, LEDs, photodetectors, lasers, etc. To further explore their potential, intrinsic properties should be thoroughly investigated. Single crystals with few defects are the best candidates to disclose a variety of interesting and important properties of these materials, ultimately, showing the increased importance of single-crystalline perovskite research. In this review, recent progress on the crystallization, investigation, and primary device applications of single-crystalline perovskites are summarized and analyzed. Further improvements in device design and preparation are also discussed.

Synergistic enhancement of Cs and Br doping in formamidinium lead halide perovskites for high performance optoelectronics

Cs and Br doped FAPbI₃ shows better phase stability as well as optoelectronic properties, furnishing it with good optoelectronic performance.

Thin single crystal perovskite solar cells to harvest below-bandgap light absorption

The efficiency of perovskite solar cells has surged in the past few years, while the bandgaps of current perovskite materials for record efficiencies are much larger than the optimal value, which makes the efficiency far lower than the Shockley–Queisser efficiency limit. Here we show that utilizing the below-bandgap absorption of perovskite single crystals can narrow down their effective optical bandgap without changing the composition. Thin methylammonium lead triiodide single crystals with tuned thickness of tens of micrometers are directly grown on hole-transport-layer covered substrates by a hydrophobic interface confined lateral crystal growth method. The spectral response of the methylammonium lead triiodide single crystal solar cells is extended to 820 nm, 20 nm broader than the corresponding polycrystalline thin-film solar cells. The open-circuit voltage and fill factor are not sacrificed, resulting in an efficiency of 17.8% for single crystal perovskite solar cells.

Thin films of halide perovskites are promising for solar cell technology but they do not perform well at the band edge due to the low optical absorption. Herein, Chen et al. fabricate a high efficiency single crystal perovskite solar cell with thicker single crystals to harvest the below-bandgap photons.