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Double perovskite halides are a class of materials with diverse chemistries that are amenable to solution-based synthesis routes, and display a range of properties for a variety of potential applications. Starting from a consideration of the octahedral and tolerance factors of ∼2000 candidate double perovskite compounds, we compute structural, electronic, and transport properties of ∼1000 using first-principles calculations based on density-functional-theory methods. The computational results have been assembled in a database that is accessible through the Materials Project online. As one potential application, double perovskites are candidates in the search for lead-free halide photovoltaic absorbers. We present the application of our database to aid the discovery of new double perovskite halide photovoltaic materials, by combining the results with optical absorption and phonon stability calculations. From three distinct classes of chemistries, 11 compounds were identified as promising solar absorbers and the complex chemical trends for band gap within each of these are analyzed, to provide guidelines for the use of substitutional alloying as a means of further tuning the electronic structure. Other possible applications of the database are also discussed.

Quantum cutting (QC) allows the conversion of high-energy photons into lower-energy photons, exhibiting great potential for infrared communications. Yb-doped perovskite nanocrystals can achieve an efficient QC process with extremely high photoluminescence quantum yield (PLQY) thanks to the favorable Yb 3+ incorporation in the perovskite structure. However, conventionally used oleic acid-oleylamine-based ligand pairs cause instability issues due to highly dynamic binding to surface states that have curbed their potential applications. Herein, zwitterionic type C3-sulfobetaine 3-(N,N-Dimethylpalmitylammonio)propanesulfonate molecule is utilized to build a strong binding state on the nanocrystals' surface through a new phosphine oxide synthesis route. Leveraging machine learning and Bayesian Optimization workflow to determine optimal synthesis conditions, near-infrared PLQY above 190% is achieved. The high PLQY is well maintained after over three months of aging, under high-flux continuous UV irradiation, and long continuous annealing. This is the first report of highly efficient and stable perovskite quantum cutters, which will drive the study of fundamental physics phenomena and near-infrared quantum communications., (© 2024 Wiley‐VCH GmbH.)

Despite a recent shift toward methylammonium (MA)-free lead-halide perovskites for perovskite solar cells, high-efficiency formamidinium lead iodide (FAPbI 3 ) devices still often require methylammonium chloride (MACl) as an additive, which evaporates away during the annealing process. In this article, it is shown that the residual MA + , however, triggers thermal instability. To investigate the possibility of an optimal concentration of MA + that may improve thermal stability, the intrinsic thermal stability of pure FA, FA-rich, MA-rich, and pure MA perovskite films (FA 1-x MA x PbI 3 , FAMA) is studied. The results show that the thermal stability of FAMA perovskites decreases with more MA + , under degradation conditions that isolate the intrinsic thermal stability of the material (i.e., without moisture and oxygen effects). X-ray diffraction (XRD), proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS), photoluminescence (PL) and UV-visible spectroscopy, and depth-profiling X-ray Photoelectron Spectroscopy (XPS) are employed to show that the observed trend is mainly due to the decomposition of the MA + cation, as opposed to other effects such as the precursor solvent and film morphologies. It is also found that the surfaces of these FAMA films are MA + rich, although this phenomenon does not appear to affect thermal stability. Finally, it is demonstrated that this trend is unaffected by the presence of Spiro-OMeTAD atop the film, and thus solar cell devices should preserve this trend., (© 2024 Wiley‐VCH GmbH.)

Colloidal perovskite quantum dots (PQDs) have emerged as highly promising single photon emitters for quantum information applications. Presently, most strategies have focused on leveraging quantum confinement to increase the nonradiative Auger recombination (AR) rate to enhance single-photon (SP) purity in all-inorganic CsPbBr 3 QDs. However, this also increases the fluorescence intermittency. Achieving high SP purity and blinking mitigation simultaneously remains a significant challenge. Here, we transcend this limitation with room-temperature synthesized weakly confined hybrid organic-inorganic perovskite (HOIP) QDs. Superior single photon purity with a low g (2) (0) < 0.07 ± 0.03 and a nearly blinking-free behavior (ON-state fraction >95%) in 11 nm FAPbBr 3 QDs are achieved at room temperature, attributed to their long exciton lifetimes ( τ X ) and short biexciton lifetimes ( τ XX ). The significance of the organic A-cation is further validated using the mixed-cation FA x Cs 1- x PbBr 3 . Theoretical calculations utilizing a combination of the Bethe-Salpeter (BSE) and k·p approaches point toward the modulation of the dielectric constants by the organic cations. Importantly, our findings provide valuable insights into an additional lever for engineering facile-synthesized room-temperature PQD single photon sources.

The power conversion efficiency (PCE) of the state-of-the-art large-area slot-die-coated perovskite solar cells (PSCs) is now over 19%, but issues with their stability persist owing to significant intrinsic point defects and a mass of surface imperfections introduced during the fabrication process. Herein, the utilization of a hydrophobic all-organic salt is reported to modify the top surface of large-area slot-die-coated methylammonium (MA)-free halide perovskite layers. Bearing two molecules, each of which is endowed with anchoring groups capable of exhibiting secondary interactions with the perovskite surfaces, the organic salt acts as a molecular lock by effectively binding to both anion and cation vacancies, substantially enhancing the materials' intrinsic stability against different stimuli. It not only reduces the ingression of external species such as oxygen and moisture, but also suppresses the egress of volatile organic components during the thermal stability testing. The treated PSCs demonstrate efficiency of 19.28% (active area of 58.5 cm 2 ) and 17.62% (aperture area of 64 cm 2 ) for the corresponding mini-module. More importantly, unencapsulated slot-die-coated mini-modules incorporating the all-organic surface modifier show ≈80% efficiency retention after 7500 h (313 days) of storage under 30% relative humidity (RH). They also remarkably retain more than 90% of the initial efficiency for over 850 h while being measured continuously., (© 2023 Wiley-VCH GmbH.)

Mixed-dimensional perovskites containing mixtures of organic cations hold great promise to deliver highly stable and efficient solar cells. However, although a plethora of relatively bulky organic cations have been reported for such purposes, a fundamental understanding of the materials' structure, composition, and phase, along with their correlated effects on the corresponding optoelectronic properties and degradation mechanism remains elusive. Herein, we systematically engineer the structures of bulky organic cations to template low-dimensional perovskites with contrasting inorganic framework dimensionality, connectivity, and coordination deformation. By combining X-ray single-crystal structural analysis with depth-profiling XPS, solid-state NMR, and femtosecond transient absorption, it is revealed that not all low-dimensional species work equally well as dopants. Instead, it was found that inorganic architectures with lesser structural distortion tend to yield less disordered energetic and defect landscapes in the resulting mixed-dimensional perovskites, augmented in materials with a longer photoluminescence (PL) lifetime, higher PL quantum yield (up to 11%), improved solar cell performance and enhanced thermal stability ( T 80 up to 1000 h, unencapsulated). Our study highlights the importance of designing templating organic cations that yield low-dimensional materials with much less structural distortion profiles to be used as additives in stable and efficient perovskite solar cells.

Extending halide perovskites' optoelectronic properties to stimuli-responsive chromism enables switchable optoelectronics, information display, and smart window applications. Here, we demonstrate a band gap tunability (chromism) via crystal structure transformation from three-dimensional FAPbBr 3 to a ⟨110⟩ oriented FA n +2 Pb n Br 3 n +2 structure using a mono-halide/cation composition (FA/Pb) tuning. Furthermore, we illustrate reversible photochromism in halide perovskite by modulating the intermediate n phase in the FA n +2 Pb n Br 3 n +2 structure, enabling greater control of the optical band gap and luminescence of a ⟨110⟩ oriented mono-halide/cation perovskite. Proton transfer reaction-mass spectroscopy carried out to precisely quantify the decomposition product reveals that the organic solvent in the film is a key contributor to the structural transformation and, therefore, the chromism in the ⟨110⟩ structure. These intermediate n phases (2 ≤ n ≤ ∞) stabilize in metastable states in the FA n +2 Pb n Br 3 n +2 system, which is accessible via strain or optical or thermal input. The structure reversibility in the ⟨110⟩ perovskite allowed us to demonstrate a class of photochromic sensors capable of self-adaptation to lighting.

Heterostructures, combining perovskite nanocrystals (PNC) and chalcogenide quantum dots, could pave a path to optoelectronic device applications by enabling absorption in the near-infrared region, tailorable electronic properties, and stable crystal structures. Ideally, the heterostructure host material requires a similar lattice constant as the guest which is also constrained by the synthesis protocol and materials selectivity. Herein, we present an efficient one-pot hot-injection method to synthesize colloidal all-inorganic cesium lead halide-lead sulfide (CsPbX 3 (X = Cl, Br, I)-PbS) heterostructure nanocrystals (HNCs) via the epitaxial growth of the perovskite onto the presynthesized PbS nanocrystals (NCs). Optical and structural characterization evidenced the formation of heterostructures. The embedding of PbS NCs into CsPbX 3 perovskite allows the tuning of the absorption and emission from 400 to 1100 nm by tuning the size and composition of perovskite HNCs. The CsPbI 3 -PbS HNCs show enhanced stability in ambient conditions. The stability, tunable optical properties, and variable band alignments accessible in this system would have implications in the design of novel optoelectronic applications such as light-emitting diodes, photodetectors, photocatalysis, and photovoltaics.

In less than a decade, organic-inorganic metal halide perovskites (MHPs) have shown tremendous progress in the field of light-emitting applications. Perovskite light-emitting diodes (PeLEDs) have reached external quantum efficiencies (EQE) exceeding 20 % and they have been recognized as a potential contender of the commercial display technologies. However, perovskite thin films in PeLEDs are generally deposited via a spin-coating process, which is not favourable for large area device fabrication. Despite the great success of solution-processed PeLEDs, very few articles have been reported on vacuum processed PeLEDs and the improvements in their optoelctronic performances are also progressing slowly. On the other hand, vacuum processing techniques are mostly used in organic LED technology as they can guarantee (i) the absence of solvent during thin-film growth, (ii) process scalability over large area substrates, and (iii) precise thin-film thickness control. This thin-film growth process is suitable for application in the advancement of a large variety of display technologies. In this Review, we present an overview of current research advances in the field of perovskite thin films grown via vacuum techniques, a study of their photophysical properties, and integration in PeLEDs for the generation of different colors. We also highlight the current challenges and future prospects for the further development of vacuum processed PeLEDs., (© 2021 Wiley-VCH GmbH.)

Metal lead halide perovskite nanocrystals have emerged as promising candidates for optoelectronic applications. However, the inclusion of toxic lead is a major concern for the commercial viability of these materials. Herein, we introduce a new family of non-toxic reduced dimension Rb 2 CuX 3 (X = Br, Cl) colloidal nanocrystals with one-dimensional crystal structure consisting [CuX 4 ] 3- ribbons isolated by Rb + cations. These nanocrystals were synthesised using a room-temperature method under ambient conditions, which makes them cost effective and scalable. Phase purity quantification was confirmed by Rietveld refinement of powder X-ray diffraction and corroborated by 87 Rb MAS NMR technique. Both samples also exhibited high thermal stability up to 500 °C, which is essential for optoelectronic applications. Rb 2 CuBr 3 and Rb 2 CuCl 3 display PL emission peaks at 387 nm and 400 nm with high PLQYs of ∼100% and ∼49%, respectively. Lastly, the first colloidal synthesis of quantum-confined rubidium copper halide-based nanocrystals opens up a new avenue to exploit their optical properties in lighting technology as well as water sterilisation and air purification.

Realization of reduced ionic (cationic and anionic) defects at the surface and grain boundaries (GBs) of perovskite films is vital to boost the power conversion efficiency of organic-inorganic halide perovskite (OIHP) solar cells. Although numerous strategies have been developed, effective passivation still remains a great challenge due to the complexity and diversity of these defects. Herein, a solid-state interdiffusion process using multi-cation hybrid halide perovskite quantum dots (QDs) is introduced as a strategy to heal the ionic defects at the surface and GBs. It is found that the solid-state interdiffusion process leads to a reduction in OIHP shallow defects. In addition, Cs + distribution in QDs greatly influences the effectiveness of ionic defect passivation with significant enhancement to all photovoltaic performance characteristics observed on treating the solar cells with Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 PbBr 3 (abbreviated as QDs-Cs5). This enables power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h., (© 2020 Wiley-VCH GmbH.)

Slow hot carrier cooling in halide perovskites holds the key to the development of hot carrier (HC) perovskite solar cells. For accurate modeling and pragmatic design of HC materials and devices, it is essential that HC temperatures are reliably determined. A common approach involves fitting the high-energy tail of the main photobleaching peak in a transient absorption spectrum with a Maxwell-Boltzmann distribution. However, this approach is problematic because of complications from the overlap of several photophysical phenomena and a lack of consensus in the community on the fitting procedures. Herein, we propose a simple approach that circumvents these challenges. Through tracking the broadband spectral evolution and accounting for bandgap renormalization and spectral line width broadening effects, our method extracts not only accurate and consistent carrier temperatures but also other important parameters such as the quasi-Fermi levels, bandgap renormalization constant, etc. Establishing a reliable method for the carrier temperature determination is a step forward in the study of HCs for next-generation perovskite optoelectronics.

Metal halide perovskite solar cells, despite achieving high power conversion efficiency (PCE), need to demonstrate high stability prior to be considered for industrialization. Prolonged exposure to heat, light, and moisture is known to deteriorate the perovskite material owing to the breakdown of the crystal structure into its non-photoactive components. In this study, we show that by combining the organic ligand 1-naphthylmethylammoinium iodide (NMAI) with methylammonium (MA) to form a mixed dimensional (NMA) 2 (MA) n-1 Pb n I 3n+1 perovskite the optical, crystallographic and morphological properties of the newly formed mixed dimensional perovskite films under thermal ageing can be retained. Indeed, under thermal ageing at 85 °C, the best performing (NMA) 2 (MA) n-1 Pb n I 3n+1 perovskites films show a stable morphology, a low PbI 2 formation rate and a significantly reduced variation of both MA-specific vibrational modes and fluorescence lifetimes as compared to the pristine MAPbI 3 films. These results highlight the role of the bulky NMA + organic cation in mixed dimensional perovskites to both inhibit the MA + diffusion and reduce the material defects, which act as non-radiative recombination centres. As a result, the thermal stability of metal halide perovskites has been substantially improved.

Growing a monocrystalline layer of lead halide perovskites directly over substrates is necessary to completely harness their stellar properties in optoelectronic devices, as the single crystals of these materials are extremely brittle. We study the crystallization mechanism of perovskites by antisolvent vapor diffusion to its precursor solution and find that heterogeneous nucleation prevails in the process, with the crystallization dish walls providing the energy to overcome the nucleation barrier. By perturbing the system using sonication, we are able to introduce homogeneously nucleated seed crystals in the precursor solution. These seeds lead to the growth of closely packed crystals over surface-modified substrates kept in the precursor solution. This crystallization process is substrate independent and scalable and can be utilized to fabricate planar optoelectronic devices. We demonstrate a methylammonium lead iodide planar crystal photoconductor with a colossal detectivity of 1.48 × 10 13 Jones.

Room-temperature spin-based electronics is the vision of spintronics. Presently, there are few suitable material systems. Herein, we reveal that solution-processed mixed-phase Ruddlesden-Popper perovskite thin-films transcend the challenges of phonon momentum-scattering that limits spin-transfer in conventional semiconductors. This highly disordered system exhibits a remarkable efficient ultrafast funneling of photoexcited spin-polarized excitons from two-dimensional (2D) to three-dimensional (3D) phases at room temperature. We attribute this efficient exciton relaxation pathway towards the lower energy states to originate from the energy transfer mediated by intermediate states. This process bypasses the omnipresent phonon momentum-scattering in typical semiconductors with stringent band dispersion, which causes the loss of spin information during thermalization. Film engineering using graded 2D/3D perovskites allows unidirectional out-of-plane spin-funneling over a thickness of ~600 nm. Our findings reveal an intriguing family of solution-processed perovskites with extraordinary spin-preserving energy transport properties that could reinvigorate the concepts of spin-information transfer.

We report the self-assembly of an extensive inter-ligand hydrogen-bonding network of octylphosphonates on the surface of cesium lead bromide nanocrystals (CsPbBr 3 NCs). The post-synthetic addition of octylphosphonic acid to oleic acid/oleylamine-capped CsPbBr 3 NCs promoted the attachment of octylphosphonate to the NC surface, while the remaining oleylammonium ligands maintained the high dispersability of the NCs in non-polar solvent. Through powerful 2D solid-state 31 P- 1 H NMR, we demonstrated that an ethyl acetate/acetonitrile purification regime was crucial for initiating the self-assembly of extensive octylphosphonate chains. Octylphosphonate ligands were found to preferentially bind in a monodentate mode through P-O - , leaving polar P[double bond, length as m-dash]O and P-OH groups free to form inter-ligand hydrogen bonds. The octylphosphonate ligand network strongly passivated the nanocrystal surface, yielding a fully-purified CsPbBr 3 NC ink with PLQY of 62%, over 3 times higher than untreated NCs. We translated this to LED devices, achieving maximum external quantum efficiency and luminance of 7.74% and 1022 cd m -2 with OPA treatment, as opposed to 3.59% and 229 cd m -2 for untreated CsPbBr 3 NCs. This represents one of the highest efficiency LEDs obtained for all-inorganic CsPbBr 3 NCs, accomplished through simple, effective passivation and purification processes. The robust binding of octylphosphonates to the perovskite lattice, and specifically their ability to interlink through hydrogen bonding, offers a promising passivation approach which could potentially be beneficial across a breadth of halide perovskite optoelectronic applications.

Next-generation displays and lighting technologies require efficient optical sources that combine brightness, color purity, stability, substrate flexibility. Metal halide perovskites have potential use in a wide range of applications, for they possess excellent charge transport, bandgap tunability and, in the most promising recent optical source materials, intense and efficient luminescence. This review links metal halide perovskites' performance as efficient light emitters with their underlying materials electronic and photophysical attributes.

Emulation of brain-like signal processing is the foundation for development of efficient learning circuitry, but few devices offer the tunable conductance range necessary for mimicking spatiotemporal plasticity in biological synapses. An ionic semiconductor which couples electronic transitions with drift-diffusive ionic kinetics would enable energy-efficient analog-like switching of metastable conductance states. Here, ionic-electronic coupling in halide perovskite semiconductors is utilized to create memristive synapses with a dynamic continuous transition of conductance states. Coexistence of carrier injection barriers and ion migration in the perovskite films defines the degree of synaptic plasticity, more notable for the larger organic ammonium and formamidinium cations than the inorganic cesium counterpart. Optimized pulsing schemes facilitates a balanced interplay of short- and long-term plasticity rules like paired-pulse facilitation and spike-time-dependent plasticity, cardinal for learning and computing. Trained as a memory array, halide perovskite synapses demonstrate reconfigurability, learning, forgetting, and fault tolerance analogous to the human brain. Network-level simulations of unsupervised learning of handwritten digit images utilizing experimentally derived device parameters, validates the utility of these memristors for energy-efficient neuromorphic computation, paving way for novel ionotronic neuromorphic architectures with halide perovskites as the active material., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

At the heart of electrically driven semiconductors lasers lies their gain medium that typically comprises epitaxially grown double heterostuctures or multiple quantum wells. The simultaneous spatial confinement of charge carriers and photons afforded by the smaller bandgaps and higher refractive index of the active layers as compared to the cladding layers in these structures is essential for the optical-gain enhancement favorable for device operation. Emulating these inorganic gain media, superb properties of highly stable low-threshold (as low as ≈8 µJ cm -2 ) linearly polarized lasing from solution-processed Ruddlesden-Popper (RP) perovskite microplatelets are realized. Detailed investigations using microarea transient spectroscopies together with finite-difference time-domain simulations validate that the mixed lower-dimensional RP perovskites (functioning as cladding layers) within the microplatelets provide both enhanced exciton and photon confinement for the higher-dimensional RP perovskites (functioning as the active gain media). Furthermore, structure-lasing-threshold relationship (i.e., correlating the content of lower-dimensional RP perovskites in a single microplatelet) vital for design and performance optimization is established. Dual-wavelength lasing from these quasi-2D RP perovskite microplatelets can also be achieved. These unique properties distinguish RP perovskite microplatelets as a new family of self-assembled multilayer planar waveguide gain media favorable for developing efficient lasers., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Carbon based perovskite solar cells (PSCs) are fabricated through easily scalable screen printing techniques, using abundant and cheap carbon to replace the hole transport material (HTM) and the gold electrode further reduces costs, and carbon acts as a moisture repellent that helps in maintaining the stability of the underlying perovskite active layer. An inorganic interlayer of spinel cobaltite oxides (Co 3 O 4 ) can greatly enhance the carbon based PSC performance by suppressing charge recombination and extracting holes efficiently. The main focus of this research work is to investigate the effectiveness of Co 3 O 4 spinel oxide as the hole transporting interlayer for carbon based perovskite solar cells (PSCs). In these types of PSCs, the power conversion efficiency (PCE) is restricted by the charge carrier transport and recombination processes at the carbon-perovskite interface. The spinel Co 3 O 4 nanoparticles are synthesized using the chemical precipitation method, and characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV-Vis spectroscopy. A screen printed thin layer of p-type inorganic spinel Co 3 O 4 in carbon PSCs provides a better-energy level matching, superior efficiency, and stability. Compared to standard carbon PSCs (PCE of 11.25%) an improved PCE of 13.27% with long-term stability, up to 2500 hours under ambient conditions, is achieved. Finally, the fabrication of a monolithic perovskite module is demonstrated, having an active area of 70 cm 2 and showing a power conversion efficiency of >11% with virtually no hysteresis. This indicates that Co 3 O 4 is a promising interlayer for efficient and stable large area carbon PSCs.

We report the high yield synthesis of about 11 nm sized CH 3 NH 3 PbBr 3 nanocrystals with near-unity photoluminescence quantum yield. The nanocrystals are formed in the presence of surface-binding ligands through their direct precipitation in a benzyl alcohol/toluene phase. The benzyl alcohol plays a pivotal role in steering the surface ligands binding motifs on the NC surface, resulting in enhanced surface-trap passivation and near-unity PLQY values. We further demonstrate that thin films from purified CH 3 NH 3 PbBr 3 nanocrystals are stable >4 months in air, exhibit high optical gain (about 520 cm -1 ), and display stable, ultralow amplified spontaneous emission thresholds of 13.9 ± 1.3 and 569.7 ± 6 μJ cm -2 at one-photon (400 nm) and two-photon (800 nm) absorption, respectively. To the best of our knowledge, the latter signifies a 5-fold reduction of the lowest reported threshold value for halide perovskite nanocrystals to date, which makes them ideal candidates for light-emitting and low-threshold lasing applications.

Altering cation and anion ratios in perovskites has proven an excellent means of tuning the perovskite properties and enhancing the performance. Recently, methylammonium/formamidinium/cesium triple-cation mixed-halide perovskites have demonstrated efficiencies up to 22 %. Similar to the widely explored methylammonium lead halide, excess PbI 2 is added to these perovskite films to enhance their performances. The excess PbI 2 is known to be beneficial for the performance. However, its impact on stability is less well known. Triple-cation perovskites deploy excess PbI 2 up to 8 %. Thus, it is imperative to analyze the role of excess PbI 2 in the degradation kinetics. In this study, the amount of PbI 2 in the triple-cation perovskite films is varied and the degradation kinetics monitored by X-ray diffraction and optical absorption spectroscopy. The inclusion of excess PbI 2 is shown to adversely affect the stability of the material. Faster degradation kinetics are observed for samples with higher PbI 2 contents. However, samples with excess PbI 2 also showed superior properties such as enhanced grain sizes and better optical absorption. Thus, careful management of the PbI 2 quantity is required to obtain better stability and alternative pathways should be explored to achieve better device performance rather than adding excess PbI 2 ., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The primary advantages of halide perovskites for light-emitting diodes (LEDs) are solution processability, direct band gap, good charge-carrier diffusion lengths, low trap density, and reasonable carrier mobility. The luminescence in 3 D halide perovskite thin films originates from free electron-hole bimolecular recombination. However, the slow bimolecular recombination rate is a fundamental performance limitation. Perovskite nanoparticles could result in improved performance but processability and cumbersome synthetic procedures remain challenges. Herein, these constraints are overcome by tailoring the 3 D perovskite as a near monodisperse nanoparticle film prepared through a one-step in situ deposition method. Replacing methyl ammonium bromide (CH 3 NH 3 Br, MABr) partially by octyl ammonium bromide [CH 3 (CH 2 ) 7 NH 3 Br, OABr] in defined mole ratios in the perovskite precursor proved crucial for the nanoparticle formation. Films consisting of the in situ formed nanoparticles displayed signatures associated with excitonic recombination, rather than that of bimolecular recombination associated with 3 D perovskites. This transition was accompanied by enhanced photoluminescence quantum yield (PLQY≈20.5 % vs. 3.40 %). Perovskite LEDs fabricated from the nanoparticle films exhibit a one order of magnitude improvement in current efficiency and doubling in luminance efficiency. The material processing systematics derived from this study provides the means to control perovskite morphologies through the selection and mixing of appropriate additives., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new broadband-emitting 2 D hybrid organic-inorganic perovskite (CyBMA)PbBr 4 based on highly flexible cis-1,3-bis(methylaminohydrobromide)cyclohexane (CyBMABr) core has been designed, synthesized, and investigated, highlighting the effects of stereoisomerism of the templating cation on the formation and properties of the resulting perovskite. The new 2 D material has high exciton binding energy of 340 meV and a broad emission spanning from 380 to 750 nm, incorporating a prominent excitonic band and a less intense broad peak at room temperature. Significant changes in the photoluminescence (PL) spectrum were observed at lower temperatures, showing remarkable enhancement in the intensity of the broadband at the cost of excitonic emission. Temperature-dependent PL mapping indicates the effective role of only a narrow band of excitonic absorption in the generation of the active channel for emission. Based on the evidences obtained from the photophysical investigations, we attributed the evolution of the broad B-band of (CyBMA)PbBr 4 to excitonic self-trapped states., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this manuscript we reveal the formation of bilayered hybrid perovskites of a new lower dimensional perovskite family, (CHMA) 2 (MA) n-1 Pb n I 3 with n = 1-5, with high ambient stability via its crystallization driven self-assembly process. The spun-coated perovskite solution tends to crystallize and undergo phase separation during annealing, resulting in the formation of 2D/3D bilayered hybrid perovskites. Remarkably, this 2D/3D hybrid perovskites possess striking moisture resistance and displays high ambient stability up to 65 days. The bilayered approach in combining 3D and 2D perovskites could lead to a new era of perovskite research for high-efficiency photovoltaics with outstanding stability, with the 3D perovskite providing excellent electronic properties while the 2D perovskite endows it moisture stability.

Methylammonium lead bromide nanoparticles are synthetized with a new ligand (11-aminoundecanoic acid hydrobromide) by a non-template method. Upon dispersion in toluene they show a remarkable photoluminescence quantum yield of 80%. In addition, the bifunctional ligand allows anchoring of the nanoparticles on a variety of conducting and semiconducting surfaces, showing bright photoluminescence with a quantum yield exceeding 50%. This opens a path for the simple and inexpensive preparation of multilayer light-emitting devices.

Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

2D perovskites is one of the proposed strategies to enhance the moisture resistance, since the larger organic cations can act as a natural barrier. Nevertheless, 2D perovskites hinder the charge transport in certain directions, reducing the solar cell power conversion efficiency. A nanostructured mixed-dimensionality approach is presented to overcome the charge transport limitation, obtaining power conversion efficiencies over 9%., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel hole-transporting molecule (F101) based on a furan core has been synthesized by means of a short, high-yielding route. When used as the hole-transporting material (HTM) in mesoporous methylammonium lead halide perovskite solar cells (PSCs) it produced better device performance than the current state-of-the-art HTM 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). The F101-HTM-based device exhibited both slightly higher Jsc (19.63 vs. 18.41 mA cm(-2) ) and Voc (1.1 vs. 1.05 V) resulting in a marginally higher power conversion efficiency (PCE) (13.1 vs. 13 %). The steady-state and time-resolved photoluminescence show that F101 has significant charge extraction ability. The simple molecular structure, short synthesis route with high yield and better performance in devices makes F101 an excellent candidate for replacing the expensive spiro-OMeTAD as HTM in PSCs., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein, the controlled synthesis of 3D hierarchical films on carbon cloth (CC) in a high yield through a hydrothermal process and their high photocatalytic properties are reported. As representative examples, the obtained ZnIn2 S4 /CdIn2 S4 composites are composed of porous nanosheets. During the hydrothermal process, l-cysteine plays an important dual role as a coordinating agent and sulfur source, which is in favor of adjusting stoichiometry of the final product and forming the nanoporous structure. This facile method can be extended to synthesize other sulfides and oxides on CC substrates, such as CoIn2 S4 , MnIn2 S4 , FeIn2 S4 , SnS2 , and Bi2 WO6 . When evaluated the photocatalytic activity, the optimized ZnIn2 S4 /CdIn2 S4 (20%)-CC with an easily recycling feature shows higher photocatalytic degradation activity for methylene blue (MB) than ZnIn2 S4 -CC, CdIn2 S4 -CC, and ZnIn2 S4 /CdIn2 S4 (20%) powder. More importantly, ZnIn2 S4 /CdIn2 S4 (20%)-CC also exhibits superior H2 production activity. The enhanced photocatalytic activity is attributed to the unique porous sheet-like structure and the formation of heterojunction. Our results could provide a promising way to develop high-performance photocatalytic films, which makes it possible to be used in real devices., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Organic-inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH3NH3PbI3, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH3NH3PbI3, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensional families that will provide the next fillip toward market viability of the perovskite solar cells.

Two new electron-rich molecules, 2,3,4,5-tetra[4,4'-bis(methoxyphenyl)aminophen-4"-yl]-thiophene (H111) and 4,4',5,5'-tetra[4,4'-bis(methoxyphenyl)aminophen-4"-yl]-2,2'-bithiophene (H112), which contain thiophene cores with arylamine side groups, are reported. When used as the hole-transporting material (HTM) in perovskite-based solar cell devices, power conversion efficiencies of up to 15.4% under AM 1.5G solar simulation were obtained. This is the highest efficiency achieved with HTMs not composed of 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) and its isomers. Both HTMs, especially H111, have great potential to replace expensive spiro-OMeTAD given their much simpler and less expensive syntheses., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We successfully utilize the concept of coalescence and room-temperature sintering to prepare morphologically different nanoparticles. n-Type chalcogenide (CuIn5 S8 ) nanocrystals are synthesized at room temperature by simple mixing of oppositely charged precursor nanoparticles. The coalescence of polycation-coated CuS nanoparticles and negatively charged In2 S3 nanoplates is driven by close contact of the particles due to electrostatic interactions. Analysis by X-ray diffraction, transmission electron microscopy (TEM) imaging, and Raman spectroscopy confirms the formation of single-phase CuIn5 S8 without traceable secondary phase. In a photovoltaic device, the use of the coalesced particles yields a power conversion efficiency of 1.8%., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Organic-inorganic lead halide perovskites have been widely used as absorbers on mesoporous TiO2 films as well as thin films in planar heterojunction solar cells, yielding very high photovoltaic conversion efficiencies. Both the addition of chloride and sequential deposition methods were successfully employed to enhance the photovoltaic performance. Here, both approaches are combined in a sequential method by spincoating PbCl2 + PbI2 on a mesoporous TiO2 film followed by the perovskite transformation. The role of Cl in determining the optical, electrical, structural and morphological properties is correlated with the photovoltaic performance. The highest photovoltaic efficiency of 14.15% with the V(oc), FF and J(sc) being 1.09 V, 0.65 and 19.91 mA cm(-2) respectively was achieved with 10 mol% of PbCl2 addition due to an increase of the film conductivity induced by a better perovskite morphology. This is linked to an improvement of the hysteresis and reproducibility of the solar cells.

Flexible three-dimensional (3D) nanoarchitectures have received tremendous interest recently because of their potential applications in wearable electronics, roll-up displays, and other devices. The design and fabrication of a flexible and robust electrode based on cobalt sulfide/reduced graphene oxide/carbon nanotube (CoS2 /RGO-CNT) nanocomposites are reported. An efficient hydrothermal process combined with vacuum filtration was used to synthesize such composite architecture, which was then embedded in a porous CNT network. This conductive and robust film is evaluated as electrocatalyst for the hydrogen evolution reaction. The synergistic effect of CoS2 , graphene, and CNTs leads to unique CoS2 /RGO-CNT nanoarchitectures, the HER activity of which is among the highest for non-noble metal electrocatalysts, showing 10 mA cm(-2) current density at about 142 mV overpotentials and a high electrochemical stability., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lead free perovskite solar cells based on a CsSnI3 light absorber with a spectral response from 950 nm is demonstrated. The high photocurrents noted in the system are a consequence of SnF2 addition which reduces defect concentrations and hence the background charge carrier density., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hierarchical CoS2 hollow nanospheres (HSs) with a nitrogen-doped-carbon coating (NC@CoS2 ) are fabricated by a simple solution method. The uniform 300 nm-sized NC@CoS2 HSs are composed of ultrathin nanosheet subunits with a thickness of around 2 nm. It was found that polyvinylpyrrolidone and ethylenediamine not only controlled the morphology of the products, but also provided the sources of nitrogen-doped carbon. Benefiting from their unique structural characteristics, hierarchical NC@CoS2 HSs can be applied in lithium-ion batteries, supercapacitors, and photocatalysis. When evaluated as an electrode material, NC@CoS2 with a coating of optimal thickness showed a high lithium-storage capability with a good cycling stability. Moreover, NC@CoS2 had a remarkable supercapacitive performance and photocatalytic activity. The attractive electrochemical and photocatalytic performances were attributed to the overall structural features of the NC@CoS2 hollow spheres: the N-doped-carbon (NC) coating, hollow interior, and ultrathin nanosheets., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Organic-inorganic metal halide perovskite solar cells were fabricated by laminating films of a carbon nanotube (CNT) network onto a CH3NH3PbI3 substrate as a hole collector, bypassing the energy-consuming vacuum process of metal deposition. In the absence of an organic hole-transporting material and metal contact, CH3NH3PbI3 and CNTs formed a solar cell with an efficiency of up to 6.87%. The CH3NH3PbI3/CNTs solar cells were semitransparent and showed photovoltaic output with dual side illuminations due to the transparency of the CNT electrode. Adding spiro-OMeTAD to the CNT network forms a composite electrode that improved the efficiency to 9.90% due to the enhanced hole extraction and reduced recombination in solar cells. The interfacial charge transfer and transport in solar cells were investigated through photoluminescence and impedance measurements. The flexible and transparent CNT network film shows great potential for realizing flexible and semitransparent perovskite solar cells.

In this work, we report a novel and feasible strategy for the practical applications of one-dimensional ultrasensitive phototransistors made of tungsten-doped VO2 single nanowires. The photoconductive response of the single nanowire device was investigated under different visible light excitations (405 nm, 532 nm, and 660 nm). The phototransistor device exhibited ultrafast photoresponse, high responsivity, broad multispectral response, and rapid saturation characteristic curves. These promising results help to promote the applications of this material in nano-scale optoelectronic devices such as efficient multispectral phototransistors and optical switches.

In this work, we report a new cobalt(III) complex, tris[2-(1H-pyrazol-1-yl)pyrimidine]cobalt(III) tris[bis(trifluoromethylsulfonyl)imide] (MY11), with deep redox potential (1.27 V vs NHE) as dopant for 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). This dopant possesses, to the best of our knowledge, the deepest redox potential among all cobalt-based dopants used in solar cell applications, allowing it to dope a wide range of hole-conductors. We demonstrate the tuning of redox potential of the Co dopant by incorporating pyrimidine moiety in the ligand. We characterize the optical and electrochemical properties of the newly synthesized dopant and show impressive spiro-to-spiro(+) conversion. Lastly, we fabricate high efficiency perovskite-based solar cells using MY11 as dopant for molecular hole-conductor, spiro-OMeTAD, to reveal the impact of this dopant in photovoltaic performance. An overall power conversion efficiency of 12% is achieved using MY11 as p-type dopant to spiro-OMeTAD., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a novel electron-rich molecule based on 3,4-ethylenedioxythiophene (H101). When used as the hole-transporting layer in a perovskite-based solar cell, the power-conversion efficiency reached 13.8 % under AM 1.5G solar simulation. This result is comparable with that obtained using the well-known hole transporting material 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). This is the first heterocycle-containing material achieving >10 % efficiency in such devices, and has great potential to replace the expensive spiro-OMeTAD given its much simpler and cheaper synthesis., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Solution processed zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated by varying the Zn/Sn composition. The addition of Sn to the zinc oxide (ZnO) films resulted in improved electrical characteristics, with devices of Zn0.7Sn0.3O composition showing the highest mobility of 7.7 cm(2)/(V s). An improvement in subthreshold swings was also observed, indicative of a reduction of the interfacial trap densities. Mobility studies at low temperature have been carried out, which indicated that the activation energy was reduced with Sn incorporation. Kelvin probe force microscopy was performed on the films to evaluate work function and correlated to the metal-semiconductor barrier indicating Zn0.7Sn0.3O films had the smallest barrier for charge injection. Organic-inorganic hybrid complementary inverters with a maximum gain of 10 were fabricated by integrating ZTO TFTs with poly-3-hexylthiophene (P3HT) transistors.

Two cyanobiphenyl liquid crystals (LCs), 5CB (4-cyano-4'-pentylbiphenyl) and 8CB (4-cyano-4'-octylbiphenyl), are introduced as additives into Co(II/III) electrolytes for dye-sensitized solar cells (DSCs). An electrolyte containing a combination of these LCs and 4-tert-butylpyridine (TBP) exhibits higher photovoltage than one with only TBP, resulting in higher power conversion efficiency.

Chemical welding of oppositely charged dissimilar metal chalcogenide nanomaterials is reported to produce a quaternary metal chalcogenide. CuSe and In2S3 nanoparticles were synthesized with opposite surface charges by stabilizing with polyacrylic acid and polydiallyldimethylammonium chloride. Upon mixing these nanoparticles at room temperature, the electrostatic attraction induced coalescence of these nanoparticles and led to the formation of CuInSxSe1-x nanoparticles.

A facile route for sensitive label-free detection of bio-toxins using aligned single walled carbon nanotubes is described. This approach involves patterning of a catalyst on the surface of a quartz substrate using a sub-100 μm stripe-patterned polydimethylsiloxane stamp for aligned carbon nanotube generation followed by fabrication of field effect transistor (FET). Atomic force microscopy, field emission scanning electron microscopy and Raman spectroscopy are employed to characterize the synthesized nanotubes. Unlike previous reports, the adopted approach enables direct electronic detection of bio-toxins with sensitivities comparable to ELISA. As a proof of concept, the fabricated FET responds to nM concentration levels (with a LOD of ∼2 nM) of epsilon toxin produced by Clostridium perfringens and a prominent food toxin. This facile approach could be customized to detect other classes of toxins and biomarkers upon appropriate functionalization of the aligned carbon nanotubes. Finally, we demonstrate the use of the FET-platform for detection of toxin in more complex matrices such as orange juice., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Zinc sulfide (ZnS) thin films have been synthesized by spray pyrolysis at 310 °C using an aqueous solution of zinc chloride (ZnCl2) and thioacetamide (TAA). Highly crystalline films were obtained by applying TAA instead of thiourea (TU) as the sulfur source. X-ray diffraction (XRD) analyses show that the films prepared by TAA contained a wurtzite structure, which is usually a high temperature phase of ZnS. The crystallinity and morphology of the ZnS films appeared to have a strong dependence on the spray rate as well. The asymmetric polar structure of the TAA molecule is proposed to be the intrinsic reason of the formation of highly crystalline ZnS at comparatively low temperatures. The violet and green emissions from photoluminescence (PL) spectroscopy reflected the sulfur and zinc vacancies in the film. Accordingly, the photodetectors fabricated using these films exhibit excellent response to green and red photons of 525 nm and 650 nm respectively, though the band gaps of the materials, estimated from optical absorption spectroscopy, are in the range of 3.5-3.6 eV.

The effect of semiconductor passivation on quantum-dot-sensitized solar cells (QDSCs) has been systematically characterized for CdS and CdS/ZnS. We have found that passivation strongly depends on the passivation agent, obtaining an enhancement of the solar cell efficiency for compounds containing amine and thiol groups and, in contrast, a decrease in performance for passivating agents with acid groups. Passivation can induce a change in the position of TiO2 conduction band and also in the recombination rate and nature, reflected in a change in the β parameter. Especially interesting is the finding that β, and consequently the fill factor can be increased with the passivation treatment. Applying this strategy, record cells of 4.65% efficiency for PbS-based QDSCs have been produced.