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Low power density radio-frequency (RF) magnetron sputtering of Ni-doped gallium oxide (Ga2O3) films offers notable advantages in terms of improved film quality and realizable band-tuning. In this research, the Ni-doped Ga2O3 films are deposited on a substrate using RF magnetron sputtering at different powers of 70–140 W. The effects of low sputtering power on the optical and chemical properties of Ni-doped Ga2O3 films are studied. The experimental results illustrate that an effective Ni doping is observed at higher than 100 W as shown by the obvious increase in the intensity of the Ni plasma radicals and the Ni atomic ratio. The Ni-doped Ga2O3 film prepared at 120 W reveals a larger cluster size and maximum ratios of Ni3+ and non-lattice oxygen, resulting in the highest values in mobility and carrier concentration of 3.5 cm2 V−1 s−1 and 5.0 × 1016 cm−3, respectively. With increasing powers, a decrease in the band gap from 5.2 to 4.8 eV is observed. The RF sputtering of Ni-doped Ga2O3 films at a lower power density, ranging from 0.18 to 0.36 W cm−2, provides an alternative in large-area industrial applications. [ABSTRACT FROM AUTHOR]

Images are traditionally interpreted through a series of spatial pixels, as exemplified by digital imaging chips that rely on silicon-based CCD and CMOS sensor technologies. However, because of the intrinsic material limitations of silicon, extending the imaging capabilities of higher signal-to-noise ratios under weak-light conditions, or to encompass gamma- and X-rays, and terahertz spectral regions presents significant challenges. Recently conceptual single-pixel imaging (SPI) represents a novel paradigm in image interpretation, offering a viable alternative that bypasses the intricate manufacturing requirements of multi-pixel arrays and enables the use of advanced, non-silicon materials. Halide perovskite emerges as a notable alternative, acclaimed for its superior photonic detection capabilities across a broad spectrum beyond the visible and its promising performance level higher than that of the state-of-the-arts. We propose that the perovskite-based SPI has the potential for cost-effective and multi-spectral imaging solutions to the existing techniques. This paper delves into the transformative impact of perovskite-based SPI, with discussions of its fundamentals, detailed imaging manifestations in different spectral regions, and its promising role in revolutionizing photonic imaging towards bidirectional extension far beyond the visible spectrum. [ABSTRACT FROM AUTHOR]

Despite the high performance of bulk hybrid perovskites, the material/device stability is a critical issue originating from the perovskites' degradation when exposed to an open-air atmosphere. 2D/quasi-2D perovskite materials have attracted much attention due to their high stability under ambient conditions compared to the bulk perovskite. Along with 2D perovskite, various charge transport materials, and additives were also employed in perovskite solar cells (PSCs). We carried out one such approach in this work, where Ti3C2Tx a typical representative of the 2-D family, called MXenes, has been employed as a passivation/interfacial layer between the quasi-2D perovskite and the hole transport layer. A PSC, passivated with MXenes, shows over 9% relative improvement in the performance and very high stability (∼99%) in an open-air atmosphere over 50 days as compared to its pristine device. The detailed investigation suggests the role of MXene as a passivator, an energy aligner, and a barrier to reduce the non-radiative recombination loss, provide pathways for effortless hole transportation, and protect from external environmental factors respectively. Moreover, transient absorption studies reveal that adding MXenes also affects the distribution and lifetime of quasi-2D phases in PSCs. As we delve into specific applications, such as the integration of MXenes as passivator/HTL interfacial layers in 2-D PSCs, we unlock the potential for enhanced device performance, showcasing MXenes as a driving force in the evolution of stable solar cell technologies. [ABSTRACT FROM AUTHOR]

In the field of perovskite solar cells (PSCs), 3D/2D heterostructures are promising candidates to obtain highly efficient and stable devices. Herein, inspired by dications that have afforded rare layered perovskites called Dion–Jacobson (DJ), with short interlayer distances, we designed and synthesized the new 2-iodopropane-1,3-diamonium dication (DicI), and we successfully obtained multi-n 2D layered perovskites (DicI)(MA)n−1PbnI3n+1 (n = 1–4, MA+ = methylammonium). As a result of a suitable size of the dication which fits well, in projection to the layer planes, in the square defined by four adjacent apical iodides, as well as halogen bonding between organic iodine and apical iodides (I(ap)) of perovskite layers, a perfect eclipsed configuration between adjacent layers takes place, yielding unprecedented short I(ap)⋯I(ap) distances, as small as 3.882 Å in (DicI)(MA)2Pb3I10. Density functional theory (DFT) calculations highlight unusually strong valence band dispersion along the Γ → Z direction. Effective masses for out-of-plane motions of holes are estimated on par with values computed for 3D perovskites, and similar to in-plane effective masses in 2D multilayered perovskites. This indicates that these layered compounds feature quasi 3D electronic structures, hence appearing as promising candidates for PSC heterostructures. [ABSTRACT FROM AUTHOR]

Over the past few years, revolutionary progress has been made in perovskite solar cells (PSCs) with the power conversion efficiency (PCE) skyrocketing from the initial 3.8% to 26.0%. However, stability issues are still holding back their commercialization process despite tremendous efforts being devoted to the research on perovskite composition regulation, additive or surface engineering, and the exploration of interfacial or charge transport materials. Recently, the cross-linking strategies involving cross-linkable organic molecules have come to the fore due to their great potential in synchronously enhancing the intrinsic, processing, thermal, and mechanical stabilities of perovskites. Hence, in this review, the recent advances in cross-linking methods utilized in PSCs are systematically summarized, including the influencing factors on device stability, the definition and mechanisms of cross-linking strategies, and the development of various functional cross-linking molecules, among which the key elaborations consist of the molecular design and related efficacy for cross-linking strategies as well as their contributions to device performance. Finally, future perspectives and directions for cross-linking strategies are provided, which are expected to gather further research momentum in exploiting more efficient and durable cross-linking approaches to realize efficient, highly stable PSCs. [ABSTRACT FROM AUTHOR]

Low-dimensional hybrid organic–inorganic perovskites have attracted a great deal of interest thanks to their high compositional and structural flexibilities that induce distinctive optoelectronic properties, for instance for light-emitting and photovoltaic applications. Here, we study at the density functional theory (DFT) level the electronic and optical properties of two one-dimensional hybrid perovskites incorporating cyanine or Victoria blue B (VBB) dye cations. Our electronic-structure analyses indicate that in both cases the highest occupied molecular orbitals of the cation dyes are nearly aligned with the band edges of the inorganic component; however, wavefunction delocalization between the two components only arises in the cyanine-perovskite system where electronic couplings can be identified, albeit weakly, between the organic dye cations and the inorganic framework. The excited-state properties of the cyanine-perovskite system were further evaluated by carrying out time-dependent DFT calculations on representative finite cluster models based on the bulk structures. The electronic couplings between the organic and inorganic components result in a small degree of charge-transfer contributions to the low-lying excited states, which in turn leads to a broadening of the lowest absorption band. [ABSTRACT FROM AUTHOR]

Dion–Jacobson (DJ) phase two-dimensional (2D) hybrid halide perovskites are promising for environmentally stable optoelectronic device applications due to their attractive photophysical properties, including long charge carrier lifetime and partially suppressed non-radiative losses. However, the atomistic details of the structure–property relationship are severely limited, which substantially restricts the strategic materials designed for these layered halide perovskites (LHPs). Here, we combine nonadiabatic molecular dynamics and time-domain density functional theory to understand the effects of spacer cation functionalization on the ground and excited-state charge carrier dynamics in DJ phase LHPs. Our in-depth study reveals that the fluorination of spacer cations considerably restricts the thermal motions of LHPs at ambient conditions. The compact structure weakens the overall electron–phonon interactions and reduces the thermal fluctuations of the band edges in real-time. These dynamic modifications partially mitigate the non-radiative recombination, prolonging the lifetime of photogenerated charge carriers. The suppressed carrier loss mechanism strongly suggests that the fluorinated spacer cation-based LHPs would exhibit enhanced performance as optoelectronic materials. These systematic simulations of excited state carrier dynamics elaborate that chemically viable functionalization of the spacer cations is a robust approach to improve the photophysical properties of 2D halide perovskites strategically. These insights also guide us to propose a few potential strategies to design highly beneficial spacer cations of LHPs that can be introduced in next-generation optoelectronic devices. [ABSTRACT FROM AUTHOR]

Compositional modifications and passivating additives have been key enablers to achieve operationally stable halide perovskite devices with excellent optoelectronic properties. The thermal and structural instability of the most desirable single-cation metal halide perovskites motivates the use of multiple cation and mixed-halide compositions that indeed lead to superior optoelectronic and photovoltaic properties over the course of the development. The application of multiple cation/anion and additive-based alloyed perovskites could, however, be hindered by the formation of non-perovskite phases and bandgap increase. Recent studies have shown that exceptional performance can be achieved using simpler compositions, such as FAPbI3, with appropriate passivation methods. In this perspective, we will present the current status of multiple cation/anion perovskites and discuss the role of common monovalent cations such as FA, MA, Cs, Rb, and K on the stability, optoelectronic properties, and charge transport behavior of lead halide perovskites. We further present the common stabilization and passivation strategies for phase-pure FAPbI3. We highlight the key role of solid-state NMR in determining the atomic-level mechanism of action of the various dopants and passivation agents. We then summarize the current understanding of the benefits and drawbacks of the cation alloying approach relative to the passivated phase-pure FAPbI3. Finally, we discuss the perspective for future research directions to achieve stable perovskite solar cells that approach the theoretical limit. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) lead-based hybrid perovskites with highly intrinsic anisotropy and entertaining semiconductor properties are well suited for polarization-sensitive photodetection. Nonetheless, their chemical instability and environmental hazards hinder their further application. Recenly, 2D double perovskites have received much attention as excellent green alternatives to lead-based perovskites. However, the application of 2D double perovskite in broad-spectrum polarization-sensitive detection has not been explored. In this work, we first grew centimeter-sized crystals (11 × 3 × 1 mm3) of 2D hybrid double perovskite (IPA)4AgBiI8 (IPA is iodopropylamine) with narrow bandgap of Eg = 1.87 eV. Remarkably, the single-crystal photodetectors of (IPA)4AgBiI8 show broad-spectrum polarization-sensitive response, even at 660 nm, with a large dichroism ratio (Iphc/Iphb ≈ 1.23), a large detectivity up to ∼1010 Jones, and a relatively rapid response time (∼450 μs). All these outstanding features combine to produce (IPA)4AgBiI8, an excellent polarized photodetector material. This work introduces a novel 2D hybrid double perovskite material for broad-spectrum polarization-sensitive photodetection. [ABSTRACT FROM AUTHOR]

Metal halide perovskites or simply known as perovskites are organic–inorganic hybrid materials that have surpassed silicon-based photovoltaic (PV) technology in terms of power-conversion efficiency (PCE). However, low environmental stability remains the key challenge to be addressed before the industrial prospects of perovskite-based PV technology are met. Ligand engineering to control dimensionality and tune optoelectronic properties of perovskites is the most attractive way to endow them with environmental stability, passivate defects, manoeuvre exciton binding energy, enhance carrier mobility, and improve carrier extraction along with the integration of other desirable properties into the perovskites. In this regard, the exploration of fluorinated spacer cations for developing perovskites for PV applications seems highly imperative. This highlight presents state-of-the-art recent developments in the area of multi-dimensional perovskites, particularly focusing on developments in the area by exploring fluorinated spacers with regard to quasi-2D and 2D/3D-bilayer perovskites to offer solutions to the key issues of stability, exciton binding energy, charge carrier mobility, defect passivation, and any other issues pertaining to perovskites for application in PV devices. Also literature reports of fluorinated spacer manifested passivation that could tailor the optoelectronic properties of perovskites for PV applications are covered. [ABSTRACT FROM AUTHOR]

Ga2O3 is attractive for power devices and solar-blind ultraviolet photodetectors due to its ultra-wide bandgap, large breakdown field, and favorable stability. However, it is difficult to prepare the ideal Ga2O3 since there are plenty of defects (e.g., vacancies and interstitial atoms) in the bulk and films which can affect the physical properties of Ga2O3. Besides, the deep level defects act as trapped centers and have influence on the sensitivity and responsivity of optoelectronic devices. It has been discovered that doping is an effective strategy to modulate the properties of Ga2O3. In this review, the effects of defects and impurities on the material properties of Ga2O3 are mainly discussed. Considering that β-Ga2O3 is the most stable and the most studied currently, it is the main focus of this review. Firstly, the intrinsic properties (e.g., electronic, absorption, thermal and mechanical properties) of β-Ga2O3 are introduced, and then the influence of impurities (e.g., dopants and passivators) and defects on the electronic properties of β-Ga2O3 is discussed emphatically. Besides, the other properties (e.g., luminescence, magnetic, and piezoelectric properties) of β-Ga2O3 modulated by defects and impurities are also briefly discussed. Meanwhile, some new research directions are also worth exploring. These problems and potential directions are summarized and discussed in the last section. [ABSTRACT FROM AUTHOR]

Lead-free hybrid perovskite materials have attracted tremendous consideration due to their applications in photovoltaics, optoelectronics, thermal sensors, etc. Herein, we isolated a new stable semiconductive 2D bismuth(III)–silver(I) iodide hybrid double perovskite formulated as (H2MPP)2[BiAgI8], where H2MPP = 1-methylpiperidinium-4-amine, with reversible solid-state thermochromism, a narrow bandgap and considerable temperature-dependent conductivity. Upon heating from 150 K to 450 K, (H2MPP)2[BiAgI8] crystals exhibit a reversible colour change between orange and dark red. The associated structural changes were monitored using in situ single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), UV-visible absorption and Raman spectroscopy. Besides, the electrical conductivity of (H2MPP)2[BiAgI8] changes over four orders of magnitude upon thermochromism (up to 1.51 × 10−6 S cm−1 at 450 K) and showed an efficiently enhanced photocurrent switching on/off ratio. Moreover, the (H2MPP)2[BiAgI8] crystals can be processed into thin films via spin coating and exhibit high stability under heat and moisture, which is indicative of their potential optoelectronic applications based on thermochromism. [ABSTRACT FROM AUTHOR]

Quasi-2D cesium lead halide perovskites exhibit better stability than 3D CsPbI3 due to the steric hindrance, decreased surface energy, and improved hydrophobicity brought by long-chain organic spacers, such as phenylethylammonium (PEA) cations. However, crystal-orientation-induced poor charge transport and phase impurities greatly limit their performance. Here, we report effective approaches to tuning the crystal orientation of quasi-2D crystalline films in inorganic cesium lead halide perovskites. By reducing the N,N-dimethylformamide/dimethyl sulfoxide ratio and introducing MACl in the precursor solutions, we are able to achieve vertically-aligned PEA2Cs3Pb4I13 perovskite films with enhanced film coverage, decreased trap density, and improved phase purity. The optimized solar cell devices show over 70% improvement in photocurrent which results in a 30% enhancement in efficiency. The unencapsulated cesium-based 2D device preserved 70% of its initial efficiency after being exposed to humid air for 30 days. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) suffer from deep level defects which would cause charge accumulation and consequent non-radiative recombination losses during the operation of the device, limiting their power conversion efficiencies (PCEs). Herein, we employ small molecule dicyandiamide (DICY) as a passivating agent for the deep level defects of perovskite thin films. The C–N bond (C–NH–C) of DICY is found to be Lewis acidic due to the inductive effect of Lewis basic imine (–C＝N) and cyano (–C≡N) functional groups of DICY. So, the synergistic effect of the functional groups in DICY could passivate the deep level defects by forming a Lewis adduct by coordination bonds, which is proved by density functional theory calculations and SCLC measurements. The elimination of the deep level defects of perovskite thin films results in a reduced charge recombination and more efficient charge transport. Consequently, the optimized PSC based on DICY shows a champion PCE of 20.05%. Our findings reveal the mechanisms of the synergistic effect of the functional groups in the small molecule on passivating the deep level defects of perovskites. [ABSTRACT FROM AUTHOR]

Heterometallic 0D metal halide hybrids, consisting of more than one kind of metal halide units, are anticipated to manifest synergistic effects on the photo-physical properties of the constituent metal halide units. Such architectures hold great promise for design and development of function-targeted materials. However, heterometallic 0D hybrids, featuring isolated metal halide units, typically do not show any synergistic effects due to large inter-unit spatial separations that inhibit interactions/coupling between the constituent metal halide units. It remains challenging to design synthetic strategies that would support structural modifications to allow synergistic electronic coupling between the metal halide units in heterometallic 0D hybrids. Here, we report synthesis and characterization of heterometallic (Sb, Mn) 0D hybrid, namely Tris SbMnCl, with isolated MnCl5 units, (Sb/Mn)Cl6 units, dispersed in the organic ligand matrix and layer of dynamic and networked water molecules. Steady state and time resolved emission spectra (TRES) analysis suggests strong synergistic interaction between the isolated metal halide units. Efficient energy transfer from the strongly absorbing Sb centres to emissive Mn centres results in the observed enhanced emission. Proton conductivity measurements together with first-principles calculations suggest the unique role of the networked water molecules in mediating the electronic coupling/energy transfer between the separated metal halide units in Tris SbMnCl hybrid. This report highlights the role of structure/composition of the synthesized heterometallic 0D hybrid in attaining electronic dimensionality higher than 0D through synergistic electronic interaction between the isolated metal halide units. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) Ruddlesden-Popper hybrid perovskites (RPHPs) have shown enormous potential for photoelectric applications owing to their advantages of structural diversity and unique physical properties. Despite extensive studies, the cage-incorporation of secondary amines (e.g., dimethylamine, DMA) to explore 2D RPHPs remains a great challenge. Herein, we present a new member of 2D RPHPs, (BA)2(DMA)Pb2Br7 (1, BA+ = n-butylammonium), for which organic DMA+ cations are enclosed in perovskite cavities. The inorganic perovskite sheets and organic BA+ spacing layers are arranged in the alternate packings, resembling a 2D quantum-well motif. This feature is advantageous for the photoconductivity properties. Consequently, the crystal-based array detectors of 1 exhibit strong photodetection performances, including high detectivity (2.0 - 1011 Jones), large responsivity (31.1 mA W-1), and fast response time (B8 ms). Moreover, its intrinsic 2D quantum-well structure endows significant anisotropy of conductivity and optical absorption, which account for the strong polarization response with a large dichroic ratio of B1.43, falling in the range of other 2D RPHPs. These results reveal the potential of 1 for photodetection and simultaneously shed light on the research on new candidates of 2D RPHPs. [ABSTRACT FROM AUTHOR]

Low-dimensional organic–inorganic metal halides have recently attracted extensive attention because of their various structures and distinguished photoelectric properties. Herein, we report a series of new zero-dimensional organic–inorganic hybrid metal halides: (TMEDA)3Bi2Cl12·H2O, (TMEDA)3Bi2Br12·H2O, (TMEDA)3Sb2Br12·H2O, and (TMEDA)5Sb6Cl28·2H2O [TMEDA = N,N,N′·trimethylethylenediamine]. (TMEDA)3M2X12·H2O (M = Bi or Sb, X = Cl or Br) crystallizes in the monoclinic space group P21/n, and (TMEDA)5Sb6Cl28·2H2O crystallizes in the orthorhombic space group Pnma. (TMEDA)3M2X12 possesses a zero-dimensional structure with the metal halide ions of [MBr6]3− isolated by the organic TMEDA2+ cations. Interestingly, the (TMEDA)5Sb6Cl28·2H2O structure consists of a combination of corner-connected octahedra [Sb4Cl18]6− and edge-shared [Sb2Cl10]4−, which is quite rare. The light emission of all these compounds was measured, and (TMEDA)3Sb2Br12·H2O exhibits the most intense luminescence. Upon 400 nm ultraviolet light excitation, (TMEDA)3Sb2Br12·H2O exhibited strong broadband yellow emission centered at 625 nm with a full-width at half-maximum of ∼150 nm originating from self-trapped excitons. This work suggests the possibility of new types of hybrid halides by introducing different metal centers and probing the structural evolution and photoluminescent properties, serving as a reference for the relationship between structure and luminescent performance and demonstrating their potential use as phosphors in light-emitting diodes. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (per-SCs) with high performance and cost-effective solution processing have been the center of interest for researchers in the past decade. Power conversion efficiencies (PCEs) have been gradually improved up to 25.2% with relatively improved stability, which is an unparalleled progress in all generations of solar cell (SC) technology. However, there are still some prevailing challenges regarding the stability and upscaling of these promising devices. Recently, 2D layered materials (LMs) have been extensively explored to overcome the prevailing challenges of poor stability (under moisture, light soaking and high temperature), halide segregation, hysteresis, involvement of toxic materials (i.e., lead), and upscaling of devices. A critical review addressing the recent developments in the use of 2D materials, especially transition metal dichalcogenides (TMDCs), is hence necessary. The development of novel synthesis and deposition techniques including liquid-metal synthesis and ultrasonic assisted spray pyrolysis has offered more efficient fabrication of 2D-LMs with controlled thickness and morphology. Effective functionalization approaches to increase the dispersability of 2D-LMs in non-polar solvents has boosted their potential application in solar cell technology as well. Moreover, compositing 2D TMDCs with suitable organic/inorganic compounds has enabled superior charge kinetics in all functional parts of per-SCs. In addition, newly developed materials such as graphyne and graphdyine along with 2D metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have been employed in per-SCs to achieve PCEs up to 20%. This review summarizes the recent progress and challenges in the application of 2D-LMs in per-SCs and outlines the future pathways to further extend the PCE of per-SCs beyond 25%. This review particularly focuses on 2D-LMs as electrode materials and additives, the underlying charge (electron–hole) transport phenomenon in the functional layers, and their chemical and structural stability. [ABSTRACT FROM AUTHOR]

Based on the P-donor ligands of triphenylphosphine and triethylphosphine, a series of IrIII(C^N)2(P-donor ligand)Cl-type complexes bearing C^N ligands with functional groups of diphenylamine and carbazole have been successfully prepared. In dilute solution, these complexes exhibit low phosphorescence quantum yields (ΦP), while much higher ΦP values can be obtained in doped films, indicating their aggregation-induced phosphorescence emission (AIPE) potential. On checking the PL spectra of these IrIII(C^N)2(P-donor ligand)Cl-type complexes in a mixture of THF and water, it has been found that the phosphorescence intensity can be effectively enhanced by increasing the water volume ratio (fw) in THF solution, confirming the obvious AIPE property. In addition, the diphenylamine group can effectively promote the hole injection ability of the concerned complexes, which can benefit the electroluminescence properties. Hence, these IrIII(C^N)2(P-donor ligand)Cl-type complexes can show very impressive EL efficiencies in solution-processed OLEDs with a maximum external quantum efficiency (ηext) of 12.8%, a current efficiency (ηL) of 47.5 cd A−1 and a power efficiency (ηP) of 39.1 lm W−1, representing the best EL results ever achieved by these types of complexes. All these results not only provide valuable information for developing new AIPE molecules but also represent an important way to develop new phosphorescent Ir(III) complexes with high EL ability. [ABSTRACT FROM AUTHOR]

Achieving high power conversion efficiency (PCE) polymer solar cells (PSCs) has been very challenging and the ultimate goal for their commercialization. Precise investigation of the active layer morphology and newer methods to process these layers has been a crucial factor to realize high PCE. There is also a rising demand for the fabrication of PSCs with a thick active layer over a large area to facilitate their commercial application. However, to achieve higher thickness it has been observed that the active layer film morphology is compromised, which in turn reduces the device performance. Many device engineering techniques have been attempted by researchers to obtain the best possible morphology for enabling better charge transport and hence improved device efficiency. Reports of achieving thick active layer PSCs along with regulation of the morphology in favour of charge transport have also appeared in the literature. This review aims to cover important device engineering techniques which have been reported in the literature for obtaining high performance PSCs by modifying the morphology and those which have been targeted to achieve thick active layers for the same. Besides including general device engineering aspects, a discussion on varying the donor (D) and acceptor (A) ratio and thermal annealing for regulating the active layer is also included. Thereafter, solvent/additive engineering and materials engineering have been discussed to understand their role in the active layer morphology and fabrication of thick film solar cells. Lastly, all the advanced device engineering methods such as solvent vapor annealing, doctor blading, and hot-casting for the fabrication of high-performance PSCs have been covered. This review will be a good tool for all researchers who are considering various device engineering methods to obtain high performance thick PSCs. [ABSTRACT FROM AUTHOR]

It has been a consensus that the exciton binding energies in two-dimensional (2D) Ruddlesden–Popper perovskites is closely correlated with the number of layers. However, the detailed recombination dynamics of excitons and free carriers in these 2D perovskites are still highly controversial. Using transient spectroscopic techniques, carrier dynamics of 2D Ruddlesden–Popper perovskites are investigated at both room and low temperatures. We confirmed that 2D perovskites of (BA)2PbI4, with the number of [PbX6]4− layers n = 1, exhibit clearly exciton characteristic properties. Meanwhile, (BA)2(MA)Pb2I7 and (BA)2(MA)2Pb3I10, n = 2 and 3, exhibit free carrier behaviour, which is inconsistent with their binding energies of more than 100 meV. Such anomalous exciton and free carrier behaviours are attributed to the effective exciton in-plane transport and dissociation by the edge state. This investigation provides novel insights into exciton and charge carrier dynamics of 2D perovskites as well as the influence of edge states. [ABSTRACT FROM AUTHOR]

Hybrid halide perovskites have progressed as eminent semiconducting materials pioneering in the domain of low-cost thin film photovoltaics. Nevertheless, the intrinsic instability of the dominant three-dimensional (3D) perovskites impedes their potential applications in industrial-scale production and commercialization. Two-dimensional (2D) perovskite structures have surfaced as an achievable resolution to this contention. In 2D perovskites, large organic cations have been introduced as spacing cations to isolate the inorganic metal halide octahedra layers and correspondingly promote the formation of quantum well superlattices. The photophysical properties of 2D perovskites can be widely tailored through the manipulation of composition, structure, and dimensionality, which provides a compelling field for researchers working in the fields of both chemistry and physics to unveil 2D perovskite materials for high-performance devices. The advancement of low-dimensional Dion–Jacobson (DJ) phase perovskites has lately attracted considerable attention in view of their appealing stability against harsh environmental conditions as well as their competitive performance in optoelectronic applications. Although the initial reports on photovoltaic solar cells (PSCs) based on DJ perovskites have exhibited comparatively poor performance, recent investigations have revealed that they have the capability to realize a high power conversion efficiency above 20%. In this review, we discuss the structural and optoelectronic characteristics of DJ perovskites, followed by a comprehensive investigation on the recent development in DJ PSCs and photodetectors. The conceivable approaches that can be deployed to expedite the advancement of DJ-based optoelectronic applications are also discussed. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) organic–inorganic hybrid perovskites are promising for next-generation optoelectronic materials due to their enhanced stability, controllable quantum well thickness and excellent photoelectric properties. The growth of large lateral size, small thickness and high-quality single crystal films is necessary for the practical application of devices. Herein, we report a gas–liquid interface crystalline route to grow BA2PbBr4 (BA = CH3CH2CH2CH2NH3+) single crystal films and achieve wafer size (38 cm2) and thinness as little as 78 nm (aspect ratio > 105). Moreover, an ultraviolet-photodetector of the single crystal thin film presents a dark current of ∼10−14 A, a detectivity of ∼1012 Jones and fast response time (τrise = 9.7 ms and τdecay = 8.8 ms). Our work provides a way to grow 2D perovskite single crystal films with large size and small thickness, which is significant for the development of perovskite-type high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

The excellent performance and stability of perovskite solar cells (PSCs) based on quasi-2D Ruddlesden–Popper perovskites (RPPs) holds promise for their commercialization. Further improvement in the performance of 2D PSCs requires a detailed understanding of the microstructure of the quasi-2D perovskite films. Based on scanning transmission electron microscopy (STEM), time-resolved photoluminescence, and transient absorption measurements, a new sandwich-like structural model is proposed to describe the phase distribution of RPPs. In contrast to the conventional gradient distribution, it is found that small-n RPPs are sandwiched between large-n RPP phase layers at the front and back sides owing to crystallization initiated from both interfaces during film formation. This sandwich-like distribution profile facilitates excitons funneling from the film interior to both surfaces for dissociation while free carriers transport via large-n channels that permeate the film to ensure efficient charge collection by the corresponding electrodes, which is favorable for high-performance photovoltaics. This discovery provides a new fundamental understanding of the operating principles of 2D PSCs and has valuable implications for the design and optimization strategies of optoelectronic devices based on quasi-2D RPPs films. [ABSTRACT FROM AUTHOR]

A self-assembled polar monolayer (SAPM) is proposed to serve as the hole-transport layer (HTL) in optoelectronic devices. To illustrate our working principle, a superior performance of organic–inorganic halide perovskite (OIHP) photodetectors and solar cells is reported. A monolayer of poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (P3HT–COOH) was prepared on an ITO anode through a self-assembled process as HTL. It was found that the self-assembled P3HT–COOH monolayer exhibited a preferential dipole orientation on the ITO and possessed an electric field pointing toward the ITO side, which produced a positive shift of lowest-dark-current-density bias and a reduced work function relative to the spin-coated film. The presence of this internal electric field in OIHP photodetectors facilitates charge collection and assists carrier transport. Additionally, the higher LUMO level of SAPM could effectively block electron injection and lower the dark current density in comparison with that made from spin-coated P3HT–COOH. As a result, an OIHP photodetector with SAPM as the HTL demonstrated a detectivity of more than 3.03 × 1013 cm Hz1/2 W−1, a response time of 95 ns, a responsivity of 0.479 AW−1, and a stable responsivity over 11 decades. Moreover, solar cells based on SAPM exhibit much better power conversion efficiency than conventional PEDOT:PSS-based devices. All these outstanding results can be extended to many other material systems, which ensure that our approach represents a key step toward the advancement in the development of cost-effective and high-performance semiconductor optoelectronic devices. [ABSTRACT FROM AUTHOR]

Quasi-two dimensional perovskites demonstrate unique excitonic properties due to their multilayer structure making them attractive for various optoelectronic applications. However, the thickness of individual perovskite sheets in wet cast quasi-2D layers tends to randomly fluctuate giving rise to a specific type of disorder, which impacts on the carrier dynamics and is rather complex and remains understudied. Here, we present a study of carrier transport in Ruddlesden–Popper type (PEA)2FAn−1PbnBr3n+1 layers of order n from one to four, and in the bulk FAPbBr3 layer. We use a light induced transient grating technique to measure the carrier diffusion coefficient directly, and the transient absorption via photoluminescence to investigate the energy relaxation pathways. We observe two distinct energy transfer processes on different time scales. Fast energy funnelling in thicker (n ≥ 3) layers is observed up to 10 ps after excitation; we attribute this to short-distance transfer of excitons to neighbouring perovskite sheets of higher order. On the longer timescale of hundreds of picoseconds, carrier in-plane transport is governed by exciton diffusion in n = 1 and 2 layers and by free carrier plasma in thicker ones. Within the carrier density range of (0.5–4) × 1019 cm−3, the exciton diffusion coefficient in n = 1, 2 increases slowly from 1 to 2.8 cm2 s−1, whereas in thicker layers the dependence is much stronger and the diffusivity grows from 0.09 to 1.9 cm2 s−1. We explain these dependencies by a higher structural order in the thinner samples and the stronger localization of carriers in thicker ones. Also, amplified spontaneous emission (ASE) is observed in thicker (n ≥ 3) layers in electron–hole plasma, as evidenced by the typical ASE line redshift upon excitation. [ABSTRACT FROM AUTHOR]

We demonstrate a simple and effective way to enhance the performance of perovskite light-emitting diodes (PeLEDs) by utilizing an alkali halide doped PEDOT:PSS as the hole transport layer (HTL). The alkali halide (NaCl) doping helped the growth of the quasi-2D perovskite phases on top of the PEDOT:PSS, it also significantly reduced the exciton quenching in PEDOT:PSS based PeLEDs. More importantly, the doping reduced the work function of the PEDOT:PSS surface, which appropriately modulated the hole injection leading to improved charge balance. This helps to control the recombination zone inside the thin perovskite emitting layer (∼10 nm). The optimized blue-green PeLEDs with the NaCl doped PEDOT:PSS HTL showed a maximum luminance of 1487 cd m−2, current efficiency of 2.16 cd A−1 with a low turn-on voltage of 3.0 V, which are 217% and 567% higher than the PeLEDs with the pristine PEDOT:PSS layer (turn-on voltage: 3.3 V), respectively. [ABSTRACT FROM AUTHOR]

We demonstrate a simple and effective way to enhance the performance of perovskite light-emitting diodes (PeLEDs) by utilizing an alkali halide doped PEDOT:PSS as the hole transport layer (HTL). The alkali halide (NaCl) doping helped the growth of the quasi-2D perovskite phases on top of the PEDOT:PSS, it also significantly reduced the exciton quenching in PEDOT:PSS based PeLEDs. More importantly, the doping reduced the work function of the PEDOT:PSS surface, which appropriately modulated the hole injection leading to improved charge balance. This helps to control the recombination zone inside the thin perovskite emitting layer (∼10 nm). The optimized blue-green PeLEDs with the NaCl doped PEDOT:PSS HTL showed a maximum luminance of 1487 cd m−2, current efficiency of 2.16 cd A−1 with a low turn-on voltage of 3.0 V, which are 217% and 567% higher than the PeLEDs with the pristine PEDOT:PSS layer (turn-on voltage: 3.3 V), respectively. [ABSTRACT FROM AUTHOR]

A series of four-coordinated PtII(C^N)(N-donor ligand)Cl-type complexes have been synthesized through combination between C^N-type and N-donor ligands with different sizes. Photophysical features, electrochemical behaviors and electroluminescent (EL) performances have been investigated in detail. Critically, the relationship between the size of organic ligands and aggregation-induced phosphorescence emission (AIPE) behaviors for these PtII(C^N)(N-donor ligand)Cl-type complexes has been characterized. With extending the dimensions of the C^N-type and/or N-donor ligands, the AIPE of these PtII(C^N)(N-donor ligand)Cl-type complexes is more likely to show up with lower H2O volumetric fractions (fw) in the THF solution of these complexes. These unique AIPE experimental results have clearly revealed a new AIE mechanism called restrained D2d deformation of the coordinating skeleton of these PtII(C^N)(N-donor ligand)Cl-type complexes from square-planar (D4h) in the ground states to the tetrahedron (Td) skeleton in the excited states. In addition, solution-processed organic light-emitting diodes (OLEDs) based on these AIPE emitters have been fabricated to characterize their EL potential. Impressive EL efficiencies with the maximum external quantum efficiency (ηext) of 25.2%, current efficiency (ηL) of 53.9 cd A−1 and power efficiency (ηP) of 43.5 lm W−1 can be achieved, indicating great potential of these PtII(C^N)(N-donor ligand)Cl-type AIPE emitters in the field of OLEDs. Importantly, this research has proposed a new AIE mechanism to promote the development of new phosphorescent AIPE complexes with great potential in the field of OLEDs. [ABSTRACT FROM AUTHOR]

Two-dimensional diamine-based perovskites are now attracting intense interest due to their enhanced ambient stability as compared to monoamine-based perovskites. Few reports to date have focused on the fundamental morphology of diamine-based perovskite single crystals and related this to their electrical properties and the further photoconductivity behaviors. Herein, we systematically investigated pentamethylenediammonium lead bromide (PDAPbBr4) and pentylammonium lead bromide (PA2PbBr4) perovskite single crystals, and explored how their morphology and structure characteristics affected their electrical properties and photodetecting performances. Notably, PDAPbBr4 perovskite exhibited distinctive smooth and continuous morphology, quite different from the rough and discontinuous morphology of PA2PbBr4 perovskite. Besides, the single organic interlayer spacer in PDAPbBr4 perovskite induced an orderly arrangement of inorganic sheets and decreased interlayer distance. With smooth, continuous morphology and shortened interlayer distance, PDAPbBr4 perovskite exhibited lower defect density and higher electrical conductivity than PA2PbBr4 perovskite. Importantly, a PDAPbBr4-based photodetector produced a responsivity of 7.92 mA W−1, a photocurrent on/off ratio of 246, and response time of 31 ms, which outperformed a PA2PbBr4-based photodetector by 387 times in responsivity, 27 times in on/off ratio, and 10 times in response time. The findings might provide a foundation for understanding the morphology characteristics of 2D perovskites and the effects on their optoelectronic performance. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) Ruddlesden–Popper perovskites have been spotlighted as photodetectors due to their tunable bandgap and high photoluminescence quantum efficiency. The performance of photodetectors is affected by grain boundaries that can trap charge carriers and thereby degrade charge transport in perovskites. To fabricate high-performance photodetectors, it is important to control the grain boundaries of the perovskite film. Here, we use a hot casting method to synthesize highly-crystalline, large-grained films of 2D Ruddlesden–Popper perovskites (C4H9NH3)2(CH3NH3)Pb2I7 for use in improving the efficiency of photodetectors. Increasing the grain size of the perovskite film alleviates the effects of grain boundaries. To control the grain size of the film, the composition of the precursor mixture N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is varied. As the DMSO content increases, the grain size of the film increases from the nanometer to the micrometer scale. Photodetectors fabricated using films with large grains show high photocurrent and on/off ratio compared to those with small grains. This method to synthesize 2D Ruddlesden–Popper perovskite films with tailored grain sizes can facilitate the fabrication of highly-efficient optoelectronic devices. [ABSTRACT FROM AUTHOR]

Antimony(III) halide based zero dimensional hybrids have gained attention as broadband emitters. Until now, quadrangular pyramidal SbX5 based and octahedral SbX6 based 0D hybrids have been reported utilizing different organic ligands demonstrating some structural tunability affecting their emissive properties. Utilizing a common organic ligand, here we demonstrate the structural tunability (quadrangular pyramidal, octahedral, or a combination thereof) of the metal halide unit in Sb(III)Cl 0D hybrids with contrasting photo-physical properties (broadband, Stokes shift, strong/weak colored emission). The structure–property–mechanism correlation of the synthesized compounds [1 (C12H52Cl18N8O4Sb3; tris Sb green); 2 (C12H50Cl14N8O3Sb2; tris Sb red); 3 (C24H88Cl25N16O4Sb3; tris Sb yellow)] identifies crucial factors that control their emissive properties. The X-ray analysis reveals the structure (1-octahedral; 2-quadrangular pyramidal; 3-combination thereof) and the order of the extent of structural distortion as 1–3 ≪ 2. The metal halide coordination environment asymmetry and its structure are observed to dictate PL emission energy (1-green; 2-red; 3-yellow) as supported by a qualitative Molecular Orbital scheme. The extent of structural distortion guides the observed Stokes shifts (1–165 nm; 2–290 nm; 3–200 nm; 1–3 < 2). Interestingly, the extent of distortion is found to be well correlated with the observed PLQY (1–45%; 2–6%; 3–43%; 1–3 ≫; 2). This report clearly demonstrates the structural tunability and the effect of the metal halide unit structure/distortion in shaping the emissive properties of 0D organic Sb(III) halide hybrids. [ABSTRACT FROM AUTHOR]

In the past few years, metal halide perovskites (MHPs) have received numerous attention for being applied in photovoltaics, light-emitting diodes and photodetectors due to their excellent optoelectronic characteristics. However, the utilization of MHPs for field-effect transistors (FETs) lags much behind, which is mainly attributed to the challenges in device fabrication and the less-than-expected performance of MHP-based FETs. Summarizing the recent developments in fabrication and performance of MHP-based FETs is essential to further optimize device fabrication processes and to enhance device performance. This review focuses on the recent advances and developments in the fabrication and performance of MHP-based FETs. To begin with, the basics of FETs are briefly introduced. Next, the advances of FETs using 3D and 2D MHPs as semiconductor layers are summarized and the strategies, which can be employed to enhance device performance, are discussed. Finally, brief conclusions and perspectives of MHP FETs are given. Overall, this review brings together important information that aids the fabrication of MHP-based FETs with reliable and enhanced performance, aiming to promote the advancement and application of MHP-based FETs. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) multilayered hybrid perovskites have emerged as a promising class of candidates for photovoltaic and photoelectric applications. Currently, most of the 2D multilayered motifs consist of primary amines, while the candidates that accommodate large-size organic cations inside the perovskite cavity as the "perovskiter" component are still scarce. Herein, we exploit a new 2D Ruddlesden–Popper hybrid perovskite, (C5H11NH3)2(CH3NH2CH3)Pb2I7 (1), in which the secondary dimethylammonium cation (i.e., CH3NH2CH3+) acts as the "perovskiter" inside the inorganic {Pb2I7}n perovskite framework. Its quantum-well like structure, formed by alternating the organic spacer (C5H11NH3+) and inorganic sheets, would facilitate the dissociation of photoexcited electron–hole pairs and improve the performance of the optoelectronic device. Consequently, the planar array detector based on high-quality crystals of 1 exhibits fascinating photoresponses, including high responsivity (∼0.67 A W−1), notable detectivity (∼1.65 × 1012 Jones), large photocurrent ratio (∼1.1 × 104) and fast responding rate (∼270 μs). These behaviors are closely associated with its strong in-plane photoactivities related to the perovskite sheets, and extremely low dark current (∼10−11 A) inhibited by the hopping barriers of organic spacer cations. This study paves the potential way to build high-performance optoelectronic devices based on the emerging 2D single-crystal hybrid perovskite materials. [ABSTRACT FROM AUTHOR]

Ruddlesden–Popper type two-dimensional (2D) perovskite solar cells (PSCs) have been intensively studied because of their high power-conversion-efficiency (PCE) and long-term stability. In this work, we improved the performance of 2D PSCs by adding an anti-solvent (chlorobenzene) into the perovskite precursors. The use of chlorobenzene could promote the crystallization of the 2D perovskite by accelerating the formation of the perovskite nuclei. Consequently, the quality of the 2D perovskite film was improved with enhanced crystallinity, enlarged grains and reduced pinholes. By adding 20% chlorobenzene into the precursor, the average PCE of the 2D PSCs was significantly improved from 9.83 to 12.91%, with simultaneous enhancements in open-circuit voltage, short-circuit current density and fill factor. Additionally, the PCE degradation of the 2D PSCs was also reduced from 21 to 13% after a 15-day duration, indicating the improved long-term stability. The best device processed from the chlorobenzene-added precursor exhibited the highest PCE of 13.35% with a stable power output and negligible hysteresis. Our research provides a simple and effective way for improving the performance of 2D PSCs. [ABSTRACT FROM AUTHOR]

A novel two-dimensional (2D) oxysulfide, Sr3.5Pb2.5Sb6O5S10, with a band gap of 1.34 eV was successfully synthesized. The device exhibits notable current density enhancement under irradiation (Jlight/Jdark = 38.7 at 10 V) as well as a steady and reversible on/off switching mode. [ABSTRACT FROM AUTHOR]

Photovoltaics based on organic–inorganic as well as all inorganic semiconducting perovskites have emerged as a high performing technology at a lower cost. Intense research carried out in this regard over the last decade has resulted in single junction power conversion efficiencies that now exceed 25%. Furthermore, combining wide-bandgap perovskites with other narrow-bandgap absorbers such as silicon has enabled efficiencies exceeding 24%. Such tandem architectures provide the possibility of increasing the power conversion efficiency with either a little increase in cost or even at a lower cost. In this review, we discuss the emerging tandem concepts that incorporate perovskites in at least one sub-cell and can also be printed on roll-to-roll manufacturing lines. Initially, we discuss the progress in the field of perovskite/silicon tandem architectures followed by a discussion on perovskite/copper indium gallium selenide tandem devices. Then, recent progress in all-perovskite tandem devices is discussed. This is then followed by developments combining perovskites and organic bulk heterojunction absorbers. Subsequently, we discuss roll-to-roll and sheet-to-sheet printing techniques that can be used for scaled-up manufacturing of the above tandem architectures, which is then followed by reported work on perovskites that have utilised these printing techniques. Finally, we discuss prospects and future directions focusing on material stability and elimination of toxic solvents that are typically used in lab-scale perovskite solar cell fabrication processes and on less well investigated applications such as energy harvesting in space. [ABSTRACT FROM AUTHOR]

The contactless characterization technique time resolved microwave conductivity (TRMC) provides a means to rapidly and unambiguously approximate carrier mobilities and lifetimes for a variety of semiconducting materials. When using a cavity-based approach however, the technique can conventionally only resolve carrier mobilities in the plane of the substrate. In solar cells, charge carriers are extracted in the direction perpendicular to the substrate, therefore it would be beneficial if one were able to evaluate the mobility in this direction also. Here we present a novel approach for resolving charge carrier mobilities in different planes within a sample. Using a range of 3D-printed sample holders, where the sample is held at various angles relative to the incident light, we are able to simultaneously resolve the mobility in the plane of the sample and out of the plane of the sample. As examples, we have studied the 3-dimensional corner-connected metal halide perovskite methylammonium lead iodide and the 2-dimensional perovskite precusor, lead iodide. [ABSTRACT FROM AUTHOR]

Perovskite nanocrystals (NCs) have aroused wide interest in the field of optoelectronics. Herein, a quantitative post-processing method is proposed to precisely alter the photoluminescence of lead halide perovskite NCs by ligand substitution using a multidentate multifunctional polymer ligand with amide, carboxylic acid and terminal double bond groups. Surprisingly, the synergistic effect of the ligand leads to a continuously blue-shifted emission over a wide visible region (∼100 nm) with increasing addition of the polymer ligand. Moreover, the full width at half maximum (fwhm) also gradually narrows, indicating the formation of a uniform particle size after the ligand surface interaction. Simultaneously, the terminal double bonds can be cross-linked with styrene to protect perovskite NCs from moisture. These results provide a new route for controllable photoluminescence regulation and preliminarily explore the correlation between the luminescence properties of perovskite NCs and polymer ligands. [ABSTRACT FROM AUTHOR]

A novel lead-free 2D perovskite, namely PEA2SnBr4, shows impressive water-resistance by retaining its original crystal structure and optical properties when placed in contact with water. Such key properties have been advantageously used for the fabrication of a novel co-catalytic system by coupling PEA2SnBr4 with graphitic carbon nitride. PEA2SnBr4/g-C3N4 composites at different metal halide perovskite loadings (5 and 15 wt%) have been prepared and tested in hydrogen photogeneration in an aqueous environment and organic dye degradation (methylene blue). The results show an impressive enhancement of H2 production of the composite with respect to the two separate components with hydrogen evolution rates up to 1600 μmol g−1 h−1 and analogous improvements in the efficiency of methylene blue degradation. The present results, providing a novel water-resistant perovskite and co-catalytic system, pave the way towards the safe, efficient and real use of metal halide perovskites in catalysis. [ABSTRACT FROM AUTHOR]

Increasing demands for new computing systems to fulfill enormous information processing have driven the development of brain-inspired neuromorphic systems that can perform fast and energy-efficient computing. Neuromorphic computing requires efficient artificial synapses. Emerging memory devices to replace complementary metal-oxide semiconductors are being evaluated. This paper reviews recent developments in artificial synapses that exploit emerging memory devices for use in neuromorphic devices and systems. The synaptic behaviors and plasticity are described to provide the analogy between biological and artificial synapses, then the operation mechanism and emulation of synaptic plasticity using various materials and structures are provided. The remaining challenges and outlooks in the development of artificial synapses that use emerging memory devices are outlined. [ABSTRACT FROM AUTHOR]

The inorganic halide perovskite CsPbI3 has shown great promise in efficient solar cells. However, α-phase CsPbI3 is thermodynamically unstable at room temperature, limiting its applications. Herein, we have successfully fabricated highly stable all-inorganic 0D/3D Cs4Pb(IBr)6/CsPbI3−xBrx mixed-dimensional perovskite solar cells. The 0D Cs4Pb(IBr)6 phase spontaneously distributes in the 3D CsPbI3−xBrx perovskite phase and facilitates the (100) preferential crystal orientation of the CsPbI3−xBrx crystals. Due to the reasonable energy level alignment and lattice match between (040) in 0D Cs4Pb(IBr)6 and (002) in 3D CsPbI3−xBrx crystals, a 0D–3D heterojunction structure formed. The defect passivation and non-radiative recombination suppression within the films effectively promote smooth carrier transport in the perovskite solar cells, boosting the efficiency to 14.77%. The devices retained 93.9% of the initial efficiency after 60 days in a nitrogen atmosphere. Moreover, a high efficiency of 10.52% has also been achieved in the 1 cm2-large solar cells due to the high uniformity and repeatability of the 0D/3D films. [ABSTRACT FROM AUTHOR]

The instability of organic-inorganic perovskites in humid air is a serious bottleneck that restricts their practical applications in optoelectronics, although tremendous achievements have been made in organic-inorganic perovskite devices. Materials engineering is believed to be one of the most direct strategies to address this issue. Mixed-dimensional organic-inorganic perovskite microcrystals, which exhibit relatively good charge carrier transport owing to the limited grain boundaries and low defect densities compared to perovskite thin films, integrate the good humidity stability of two-dimensional (2D) and single-phase quasi-2D perovskites and the high photoresponse of 3D perovskites in an individual crystal, rendering them as excellent candidates for the development of high-performance photodetectors. Herein, the (C6 H5CH2CH2NH3, PEA)2(CH3 NH3, MA)n-1PbnBr3n+1 (n = 1, 3, 5, N) perovskite microcrystals were synthesized using an anti-solvent vapor-assisted method, and the optoelectronic properties of these microcrystals were investigated by fabricating photodetectors in a lateral configuration. The (PEA)2(MA)2Pb3Br10 and (PEA)2(MA)4 Pb5Br16 perovskites proved to be mixed-dimensional microcrystals, respectively, which consist of the single phases of 2D (PEA)2PbBr4, quasi-2D perovskite, and 3D MAPbBr3. The photodetectors based on the individual (PEA)2(MA)2Pb3Br10 and (PEA)2(MA)4Pb5Br16 perovskite microcrystals perform better than the (PEA)2PbBr4 microcrystal photodetector and exhibit higher humidity resistance than the MAPbBr3 device. The best performances are achieved in the (PEA)2 (MA)4Pb5Br16 microcrystal photodetector with a high responsivity of 182.63 A W1, detectivity of 2.51 × 1014 Jones, and gain of 5.58 × 102, which can detect an optical signal with an extremely low light power density of 2.47 nW cm-2. Our results demonstrate that developing mixed-dimensional perovskite microcrystals is a promising way to construct highly efficient and stable photodetectors. [ABSTRACT FROM AUTHOR]

To fight against the counteractive triplet–triplet annihilation and vibrational deactivation faced by low bandgap phosphorescent emitters, aggregation-induced phosphorescent enhancement (AIPE)-active deep-red and NIR emissive iridium(III) complexes are designed by suitably anchoring electron-withdrawing substituents such as -phenyl (Ir2), -ethyl ester (Ir3), and -trifluoromethyl (Ir4) groups on the N-coordinating quinoline moiety of a (benzo[b]thiophen-2-yl)quinoline cyclometalated ligand along with ancillary picolinate. The fundamentals of the origin of AIPE on Ir2 and Ir4 and its associated excited-state properties are deeply studied through comparison with unsubstituted Ir1 with the help of density functional theory and single-crystal X-ray diffraction analysis. Most importantly, AIPE-active Ir2 is employed for the development of efficient deep-red and NIR PhOLEDs by hybrid solution-processable methods, in which the AIPE effect of Ir2 reaches a maximum external quantum efficiency (EQE) of 7.29% at high doping ratios. [ABSTRACT FROM AUTHOR]

Low-dimensional perovskites have been regarded as the heir of traditional perovskites because of their tailorable structures and the resultant optoelectronic properties as well as the higher stability under ambient conditions, giving them better potential in optoelectronic devices with long term stability. To date, most 2D perovskites are constructed from large organic cations as a spacer, sandwiched between the inorganic octahedron layers to form layered structures. Other than A-site constituent engineering, in recent years, it was reported that the perovskite layers can be divided by suitable X-site components, increasing the possibility of many different 2D perovskite structures and possibly leading to a bright future. In this review, we first digest the latest developments in low dimensional perovskites, including the different phases and the unique optoelectronic properties of 2D perovskites. Subsequently, different approaches to constructing 2D perovskites will be discussed in detail, involving the traditional way of altering A-site cations and the latest way of varying X-site anions. The basic principle of partioning 2D perovskite layers from the X-site constituents will be particularly focused on. The review is aimed at providing readers with an innovative viewpoint for fashioning 2D perovskites and possible future research directions for next generation 2D perovskites. Finally, a conclusion and outlook for future prospects in 2D perovskite structures will also be delivered. [ABSTRACT FROM AUTHOR]

Ir(III) complexes have been widely used in bio-imaging, photocatalysis and chemical sensing. Five cyclometalated Ir(III) complexes (Ir1–Ir5) were synthesized and characterized. Among them, Ir2, Ir3 and Ir4 can exhibit high luminescence efficiency and relatively long phosphorescence lifetimes. Ir2, Ir3 and Ir4 are suitable for imaging and tracking of mitochondria due to their better photostability and luminescence quantum yields compared to commercially available mitochondrial trackers. Ir2, Ir3 and Ir4 displayed significant aggregation-induced emission behaviors from restricted intramolecular motion. Confocal microscopy showed that these complexes accumulate selectively in the mitochondria. Cell cytotoxicity investigations revealed that the Ir(III) complexes showed negligible cytotoxicity at the concentrations used. Our study provides insight into the relationship between the structure and the physical properties. These results indicate that these Ir(III) complexes are suitable for mitochondrial imaging in living cells. [ABSTRACT FROM AUTHOR]

Saturation magnetic moment (Msm) is a key evaluation parameter of diluted magnetic semiconductors (DMSs). The higher the Msm, the more widespread the applications of electron spin for non-volatile information manipulation and storage. In this paper, first-principles simulations predicted that cation-deficient γ-Ga2O3, having an intrinsic magnetic moment per formula unit cell of about 1 μB, is an inherent candidate to prepare DMS with high Msm. To activate the potential of its magnetism, Fe was introduced as a dopant. A thermostable Fe-doped γ-Ga2O3 thin film with high room temperature (RT) Msm of 5.73 μB/Fe was first obtained using the laser molecular beam epitaxy (L-MBE) technique. While combining theoretical calculations and experimental data, the main source of RT ferromagnetism could be ascribed to the strong ferromagnetic (FM) coupling between Fe ions, p–d orbital overlap of the Fe–O bond, and defects. Our results provide a feasible model for designing high-performance γ-Ga2O3-based DMSs. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) hexagonal boron nitride (h-BN) is a promising candidate as a supporting substrate, a gate dielectric and a protecting layer for 2D electronic and photonic devices. Transition metals were usually adopted as substrates for the synthesis of 2D h-BN, however, catalyst-free growth of high-quality h-BN on dielectric substrates is still very challenging. Herein, we report the catalyst-free growth of 2D h-BN few-layers on sapphire substrates by ion beam sputtering deposition (IBSD). We find that the h-BN grown under conventional conditions is nonstoichiometric with an excess of B element, resulting in a large number of N vacancy defects and poor crystalline quality. The wafer-scale high quality 2D h-BN layers were synthesized on sapphire by the combination of surface nitridation and N+ sputtering. Furthermore, the 2D h-BN few-layers on sapphire were used to fabricate deep ultraviolet photodetectors, which exhibit better performance in comparison with the devices fabricated by the transferred h-BN. [ABSTRACT FROM AUTHOR]

In this work, a new type of photoconductor with high responsivity and gain over a wide spectral range of DUV to NIR using a wide band gap amorphous gallium oxide (a-Ga2O3) thin film was reported for the first time. The responsivity (gain) at deep UV-250, UV-350, VIS-525 and NIR-850 nm is as high as 1099 (5438), 265 (936), 205 (483) and 122 A W−1 (178), respectively. More interestingly, we demonstrate that a novel "thermal relaxation" (TR) process (short-time heating) can effectively reduce the dark current and improve the response recovery time from hours to seconds without reducing the gain of the a-Ga2O3 detector. The mechanism related to oxygen vacancies and thermal energy and tail state excitation is proposed to explain our experimental phenomena. This result suggests that amorphous Ga2O3 films have potential applications in high-performance broadband photodetecting devices. [ABSTRACT FROM AUTHOR]

Aggregation-induced emission (AIE) has been a vitally important research topic on luminescent materials. AIE-active emitters are usually developed based on the mechanisms of restriction of intramolecular rotation (RIR) or restriction of intramolecular vibration (RIV). Herein, we report a simple phosphorescent Pt(II) complex DPA-Pt that shows impressive AIE behavior mainly because of a new mechanism. In THF/H2O mixture solutions with the water fraction (fw) increasing from 0 to 60%, DPA-Pt shows rather weak phosphorescence with the intensities slowly increasing and the emission profiles remaining almost unchanged. Once the fw reached 70–90%, the emissions are greatly enhanced with new peaks appearing and shifting to longer wavelengths. The emission of the vacuum-deposited DPA-Pt neat film is further red-shifted to the deep-red/near-infrared (NIR) region with the photoluminescence quantum yield (PLQY) markedly increased to 0.33. The experimental and theoretical results indicate that the significant enhancement and red-shift of emissions from in dilute solution to aggregation are mainly triggered by the radiative-transition-switch (RTS) from the intra-ligand charge transfer (ILCT) to the metal–metal-to-ligand charge transfer (MMLCT), indicating that RTS is a new mechanism behind this AIE phenomenon. The non-doped OLED based on DPA-Pt exhibits deep-red/NIR emission with a peak external quantum efficiency of 9.8%, which is not only higher than that of the 6 wt% doped device based on DPA-Pt, but also much higher than those reported for the state-of-the-art non-doped deep-red/NIR OLEDs based on other AIE-active emitters. [ABSTRACT FROM AUTHOR]