Showing papers on "Thin film published in 2015"
TL;DR: A solution-based hot-casting technique is demonstrated to grow continuous, pinhole-free thin films of organometallic perovskites with millimeter-scale crystalline grains that are applicable to several other material systems plagued by polydispersity, defects, and grain boundary recombination in solution-processed thin films.
Abstract: State-of-the-art photovoltaics use high-purity, large-area, wafer-scale single-crystalline semiconductors grown by sophisticated, high-temperature crystal growth processes. We demonstrate a solution-based hot-casting technique to grow continuous, pinhole-free thin films of organometallic perovskites with millimeter-scale crystalline grains. We fabricated planar solar cells with efficiencies approaching 18%, with little cell-to-cell variability. The devices show hysteresis-free photovoltaic response, which had been a fundamental bottleneck for the stable operation of perovskite devices. Characterization and modeling attribute the improved performance to reduced bulk defects and improved charge carrier mobility in large-grain devices. We anticipate that this technique will lead the field toward synthesis of wafer-scale crystalline perovskites, necessary for the fabrication of high-efficiency solar cells, and will be applicable to several other material systems plagued by polydispersity, defects, and grain boundary recombination in solution-processed thin films.
2,960 citations
TL;DR: The homologous 2D halide perovskites define a promising class of stable and efficient light-absorbing materials for solid-state photovoltaics and other applications.
Abstract: We report on the fabrication and properties of the semiconducting 2D (CH3(CH2)3NH3)2(CH3NH3)n–1PbnI3n+1 (n = 1, 2, 3, and 4) perovskite thin films. The band gaps of the series decrease with increasing n values, from 2.24 eV (CH3(CH2)3NH3)2PbI4 (n = 1) to 1.52 eV CH3NH3PbI3 (n = ∞). The compounds exhibit strong light absorption in the visible region, accompanied by strong photoluminescence at room temperature, rendering them promising light absorbers for photovoltaic applications. Moreover, we find that thin films of the semi-2D perovskites display an ultrahigh surface coverage as a result of the unusual film self-assembly that orients the [PbnI3n+1]− layers perpendicular to the substrates. We have successfully implemented this 2D perovskite family in solid-state solar cells, and obtained an initial power conversion efficiency of 4.02%, featuring an open-circuit voltage (Voc) of 929 mV and a short-circuit current density (Jsc) of 9.42 mA/cm2 from the n = 3 compound. This result is even more encouraging con...
1,589 citations
TL;DR: The preparation of high-mobility 4-inch wafer-scale films of monolayer molybdenum disulphide and tungsten disulPHide, grown directly on insulating SiO2 substrates, with excellent spatial homogeneity over the entire films are reported, a step towards the realization of atomically thin integrated circuitry.
Abstract: The large-scale growth of semiconducting thin films forms the basis of modern electronics and optoelectronics. A decrease in film thickness to the ultimate limit of the atomic, sub-nanometre length scale, a difficult limit for traditional semiconductors (such as Si and GaAs), would bring wide benefits for applications in ultrathin and flexible electronics, photovoltaics and display technology. For this, transition-metal dichalcogenides (TMDs), which can form stable three-atom-thick monolayers, provide ideal semiconducting materials with high electrical carrier mobility, and their large-scale growth on insulating substrates would enable the batch fabrication of atomically thin high-performance transistors and photodetectors on a technologically relevant scale without film transfer. In addition, their unique electronic band structures provide novel ways of enhancing the functionalities of such devices, including the large excitonic effect, bandgap modulation, indirect-to-direct bandgap transition, piezoelectricity and valleytronics. However, the large-scale growth of monolayer TMD films with spatial homogeneity and high electrical performance remains an unsolved challenge. Here we report the preparation of high-mobility 4-inch wafer-scale films of monolayer molybdenum disulphide (MoS2) and tungsten disulphide, grown directly on insulating SiO2 substrates, with excellent spatial homogeneity over the entire films. They are grown with a newly developed, metal-organic chemical vapour deposition technique, and show high electrical performance, including an electron mobility of 30 cm(2) V(-1) s(-1) at room temperature and 114 cm(2) V(-1) s(-1) at 90 K for MoS2, with little dependence on position or channel length. With the use of these films we successfully demonstrate the wafer-scale batch fabrication of high-performance monolayer MoS2 field-effect transistors with a 99% device yield and the multi-level fabrication of vertically stacked transistor devices for three-dimensional circuitry. Our work is a step towards the realization of atomically thin integrated circuitry.
1,499 citations
TL;DR: The current technologies for multilayer thin-film deposition using layer-by-layer assembly are reviewed, and the different properties and applications arising from the technologies are discussed.
Abstract: Multilayer thin films have garnered intense scientific interest due to their potential application in diverse fields such as catalysis, optics, energy, membranes, and biomedicine Here we review the current technologies for multilayer thin-film deposition using layer-by-layer assembly, and we discuss the different properties and applications arising from the technologies We highlight five distinct routes of assembly—immersive, spin, spray, electromagnetic, and fluidic assembly—each of which offers material and processing advantages for assembling layer-by-layer films Each technology encompasses numerous innovations for automating and improving layering, which is important for research and industrial applications Furthermore, we discuss how judicious choice of the assembly technology enables the engineering of thin films with tailor-made physicochemical properties, such as distinct-layer stratification, controlled roughness, and highly ordered packing
1,235 citations
TL;DR: In this paper, it was shown that hydrated crystal phases are formed when methylammonium lead iodide perovskite (MAPI) is exposed to water vapor at room temperature and these phase changes are fully reversed when the material is subsequently dried.
Abstract: Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that (i) hydrated crystal phases are formed when MAPI is exposed to water vapor at room temperature and (ii) these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was observed using time-resolved XRD and ellipsometry of thin films prepared using “solvent engineering”, single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH3NH3PbI3·H2O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single-crystal optical constants and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were m...
1,079 citations
TL;DR: It is found that by using a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster, which allows us to obtain ultrasmooth and almost pinhole-free perovSKite films by a simple one-step solution coating with only a few minutes annealing.
Abstract: To date, there have been a plethora of reports on different means to fabricate organic-inorganic metal halide perovskite thin films; however, the inorganic starting materials have been limited to halide-based anions. Here we study the role of the anions in the perovskite solution and their influence upon perovskite crystal growth, film formation and device performance. We find that by using a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster, which allows us to obtain ultrasmooth and almost pinhole-free perovskite films by a simple one-step solution coating with only a few minutes annealing. This synthesis leads to improved device performance in planar heterojunction architectures and answers a critical question as to the role of the anion and excess organic component during crystallization. Our work paves the way to tune the crystal growth kinetics by simple chemistry.
829 citations
TL;DR: Large area, flexible thin-film black gold membranes are demonstrated, which have multiscale structures of varying metallic nanoscale gaps (0–200 nm) as well as microscale funnel structures that allow heat localization within the few micrometre-thick layer and continuous water provision through micropores.
Abstract: Efficient steam generation under solar irradiation is of interest for energy harvesting applications. Here, Bae et al. develop a plasmonic nanofocusing film consisting of metal coated alumina nanowires to efficiently generate solar vapour with an efficiency up to 57% at 20 kWm−2.
748 citations
TL;DR: The coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.
Abstract: The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin ( 5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.
740 citations
TL;DR: In this article, a simple, non-toxic and low-cost antimony selenide (Sb2Se3) material with an optimal solar bandgap of ∼1.1
Abstract: Solar cells based on inorganic absorbers, such as Si, GaAs, CdTe and Cu(In,Ga)Se2, permit a high device efficiency and stability. The crystals’ three-dimensional structure means that dangling bonds inevitably exist at the grain boundaries (GBs), which significantly degrades the device performance via recombination losses. Thus, the growth of single-crystalline materials or the passivation of defects at the GBs is required to address this problem, which introduces an added processing complexity and cost. Here we report that antimony selenide (Sb2Se3)—a simple, non-toxic and low-cost material with an optimal solar bandgap of ∼1.1 eV—exhibits intrinsically benign GBs because of its one-dimensional crystal structure. Using a simple and fast (∼1 μm min–1) rapid thermal evaporation process, we oriented crystal growth perpendicular to the substrate, and produced Sb2Se3 thin-film solar cells with a certified device efficiency of 5.6%. Our results suggest that the family of one-dimensional crystals, including Sb2Se3, SbSeI and Bi2S3, show promise in photovoltaic applications. Materials with a one-dimensional crystal structure, such as antimony selenide, show considerable potential for making efficient thin-film solar cells.
700 citations
TL;DR: In this paper, a two-step deposition approach is described for the preparation of large grain (>1 μm) and continuous thin films of the lead-free layered perovskite derivative Cs3Sb2I9.
Abstract: Computational, thin-film deposition, and characterization approaches have been used to examine the ternary halide semiconductor Cs3Sb2I9. Cs3Sb2I9 has two known structural modifications, the 0-D dimer form (space group P63/mmc, no. 194) and the 2-D layered form (P3m1, no. 164), which can be prepared via solution and solid-state or gas-phase reactions, respectively. Our computational investigations suggest that the layered form, which is a one-third Sb-deficient derivative of the ubiquitous perovskite structure, is a potential candidate for high-band gap photovoltaic (PV) applications. In this work, we describe details of a two-step deposition approach that enables the preparation of large grain (>1 μm) and continuous thin films of the lead-free layered perovskite derivative Cs3Sb2I9. Depending on the deposition conditions, films that are c-axis oriented or randomly oriented can be obtained. The fabricated thin films show enhanced stability under ambient air, compared to methylammonium lead(II) iodide per...
596 citations
TL;DR: It is demonstrated that the addition of hypophosphorous acid in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices.
Abstract: Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I−, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.
TL;DR: A facile but efficient method of modifying the ZnO-coated substrates with 3-aminopropanioc acid (C3-SAM) to direct the crystalline evolution and achieve the optimal morphology of CH3NH3PbI3 perovskite film is developed.
Abstract: Morphology control is critical to achieve high efficiency CH3NH3PbI3 perovskite solar cells (PSC). The surface properties of the substrates on which crystalline perovskite thin films form are expected to affect greatly the crystallization and, thus, the resulting morphology. However, this topic is seldom examined in PSC. Here we developed a facile but efficient method of modifying the ZnO-coated substrates with 3-aminopropanioc acid (C3-SAM) to direct the crystalline evolution and achieve the optimal morphology of CH3NH3PbI3 perovskite film. With incorporation of the C3-SAM, highly crystalline CH3NH3PbI3 films were formed with reduced pin-holes and trap states density. In addition, the work function of the cathode was better aligned with the conduction band minimum of perovskite for efficient charge extraction and electronic coupling. As a result, the PSC performance remarkably increased from 9.81(±0.99)% (best 11.96%) to 14.25(±0.61)% (best 15.67%). We stress the importance of morphology control through ...
TL;DR: This work has identified that excess organic component can reduce the colloidal size of and tune the morphology of the coordination framework in relation to final perovskite grains and partial chlorine substitution can accelerate the crystalline nucleation process of perovkite.
Abstract: The precursor of solution-processed perovskite thin films is one of the most central components for high-efficiency perovskite solar cells. We first present the crucial colloidal chemistry visualization of the perovskite precursor solution based on analytical spectra and reveal that perovskite precursor solutions for solar cells are generally colloidal dispersions in a mother solution, with a colloidal size up to the mesoscale, rather than real solutions. The colloid is made of a soft coordination complex in the form of a lead polyhalide framework between organic and inorganic components and can be structurally tuned by the coordination degree, thereby primarily determining the basic film coverage and morphology of deposited thin films. By utilizing coordination engineering, particularly through employing additional methylammonium halide over the stoichiometric ratio for tuning the coordination degree and mode in the initial colloidal solution, along with a thermal leaching for the selective release of ex...
TL;DR: In this article, the authors systematically investigated the origin of the thermal instability of perovskite solar cells fabricated using ZnO electron transport layers, and they showed that the basic nature of the znO surface leads to proton-transfer reactions at the CH3NH3PbI3 interface.
Abstract: The rapid development of organometal halide perovskite solar cells has led to reports of power conversion efficiencies of over 20%. Despite this excellent performance, their instability remains the major challenge limiting their commercialization. In this report, we systematically investigate the origin of the thermal instability of perovskite solar cells fabricated using ZnO electron transport layers. Through in situ grazing incidence X-ray diffraction experiments and density functional theory calculations, we show that the basic nature of the ZnO surface leads to proton-transfer reactions at the ZnO/CH3NH3PbI3 interface, which results in decomposition of the perovskite film. The decomposition process is accelerated by the presence of surface hydroxyl groups and/or residual acetate ligands; calcination of the ZnO layer results in a more thermally stable ZnO/CH3NH3PbI3 interface, albeit at the cost of a small decrease in power conversion efficiency.
TL;DR: The complex refractive index of planar CH3NH3PbI3 thin films at room temperature is investigated by variable angle spectroscopic ellipsometry and spectrophotometry and results agree well with previously reported data of the absorption coefficient and are consistent with Kramers-Kronig transformations.
Abstract: The complex refractive index (dielectric function) of planar CH3NH3PbI3 thin films at room temperature is investigated by variable angle spectroscopic ellipsometry and spectrophotometry. Knowledge of the complex refractive index is essential for designing photonic devices based on CH3NH3PbI3 thin films such as solar cells, light-emitting diodes, or lasers. Because the directly measured quantities (reflectance, transmittance, and ellipsometric spectra) are inherently affected by multiple reflections, the complex refractive index has to be determined indirectly by fitting a model dielectric function to the experimental spectra. We model the dielectric function according to the Forouhi-Bloomer formulation with oscillators positioned at 1.597, 2.418, and 3.392 eV and achieve excellent agreement with the experimental spectra. Our results agree well with previously reported data of the absorption coefficient and are consistent with Kramers-Kronig transformations. The real part of the refractive index assumes a value of 2.611 at 633 nm, implying that CH3NH3PbI3-based solar cells are ideally suited for the top cell in monolithic silicon-based tandem solar cells.
IBM1
TL;DR: In this article, a structural study on the origin of ferroelectricity in Gd doped HfO2 thin films is presented, which provides unambiguous evidence for the existence of a non-centrosymmetric orthorhombic phase that can support spontaneous polarization.
Abstract: Here, we present a structural study on the origin of ferroelectricity in Gd doped HfO2 thin films. We apply aberration corrected high-angle annular dark-field scanning transmission electron microscopy to directly determine the underlying lattice type using projected atom positions and measured lattice parameters. Furthermore, we apply nanoscale electron diffraction methods to visualize the crystal symmetry elements. Combined, the experimental results provide unambiguous evidence for the existence of a non-centrosymmetric orthorhombic phase that can support spontaneous polarization, resolving the origin of ferroelectricity in HfO2 thin films.
TL;DR: A comprehensive and well-controlled study of the effect of moisture exposure on methylammonium lead halide perovskite film formation and properties finds that films formed in higher humidity atmospheres have a less continuous morphology but significantly improved photoluminescence, and that film formation is faster.
Abstract: Moisture, in the form of ambient humidity, has a significant impact on methylammonium lead halide perovskite films. In particular, due to the hygroscopic nature of the methylammonium component, moisture plays a significant role during film formation. This issue has so far not been well understood and neither has the impact of moisture on the physical properties of resultant films. Herein, we carry out a comprehensive and well-controlled study of the effect of moisture exposure on methylammonium lead halide perovskite film formation and properties. We find that films formed in higher humidity atmospheres have a less continuous morphology but significantly improved photoluminescence, and that film formation is faster. In photovoltaic devices, we find that exposure to moisture, either in the precursor solution or in the atmosphere during formation, results in significantly improved open-circuit voltages and hence overall device performance. We then find that by post-treating dry films with moisture exposure,...
TL;DR: It is demonstrated that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-Trapping, i.e., WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance.
Abstract: There is keen interest in the use of amorphous WO3 thin films as cathodic electrodes in transmittance-modulating electrochromic devices1–4. However, these films suer from ion-trapping-induced degra ...
TL;DR: In this article, a non-crystalline thin films of chalcogenide Cd 50 S 50−x Se x system were obtained by thermal evaporation technique onto a pre-cleaned glass substrate at a vacuum of 8.2 × 10 −4 ǫ.
TL;DR: The ferroelectric properties and crystal structure of doped HfO2 thin films were investigated for different thicknesses, electrode materials, and annealing conditions in this paper.
Abstract: The ferroelectric properties and crystal structure of doped HfO2 thin films were investigated for different thicknesses, electrode materials, and annealing conditions Metal-ferroelectric-metal capacitors containing Gd:HfO2 showed no reduction of the polarization within the studied thickness range, in contrast to hafnia films with other dopants A qualitative model describing the influence of basic process parameters on the crystal structure of HfO2 was proposed The influence of different structural parameters on the field cycling behavior was examined This revealed the wake-up effect in doped HfO2 to be dominated by interface induced effects, rather than a field induced phase transition TaN electrodes were shown to considerably enhance the stabilization of the ferroelectric phase in HfO2 compared to TiN electrodes, yielding a Pr of up to 35 μC/cm2 This effect was attributed to the interface oxidation of the electrodes during annealing, resulting in a different density of oxygen vacancies in the Gd:Hf
TL;DR: In this article, molecular dynamics simulations aimed at unraveling the atomistic details of the interaction between the methylammonium lead iodide (MAPbI3) perovskite surfaces and a liquid water environment are presented.
Abstract: Protecting organohalide perovskite thin films from water and ambient humidity represents a paramount challenge for the commercial uptake of perovskite solar cells and, in general, of related optoelectronic devices. Therefore, understanding the perovskite/water interface is of crucial importance. As a step in this direction, here we present ab initio molecular dynamics simulations aimed at unraveling the atomistic details of the interaction between the methylammonium lead iodide (MAPbI3) perovskite surfaces and a liquid water environment. According to our calculations, MAI-terminated surfaces undergo a rapid solvation process, driven by the interaction of water molecules with Pb atoms, which prompts the release of I atoms. PbI2-terminated surfaces, instead, seem to be more robust to degradation, by virtue of the stronger (shorter) Pb–I bonds formed on these facets. We also observe the incorporation of a water molecule into the PbI2-terminated slab, which could represent the first step in the formation of a...
TL;DR: Low-temperature, solution-processable Cu-doped NiOX (Cu:NiOx ), prepared via combustion chemistry, is demonstrated as an excellent hole-transporting layer (HTL) for thin-film perovskite solar cells (PVSCs).
Abstract: Low-temperature, solution-processable Cu-doped NiOX (Cu:NiOx ), prepared via combustion chemistry, is demonstrated as an excellent hole-transporting layer (HTL) for thin-film perovskite solar cells (PVSCs). Its good crystallinity, conductivity, and hole-extraction properties enable the derived PVSC to have a high power conversion efficiency (PCE) of 17.74%. Its general applicability for various elecrode materials is also revealed.
TL;DR: In this article, the current status of CH3NH3PbX3 (X = I, Br, Cl) based photovoltaic devices and their properties are discussed.
Abstract: Perovskite solar cells have received considerable attention in recent years as a promising material capable of developing high performance photovoltaic devices at a low cost. Their high absorption coefficient, tunable band gap, low temperature processing and abundant elemental constituents provide numerous advantages over most thin film absorber materials. In this review, we discuss the current status of CH3NH3PbX3 (X = I, Br, Cl) based photovoltaic devices and provide a comprehensive review of CH3NH3PbX3 device structures, film properties, fabrication methods, and photovoltaic performance. We emphasize the importance of perovskite film formation and properties in achieving highly efficient photovoltaic devices. The flexibility and simplicity of perovskite fabrication methods allow use of mesoporous and planar device architectures. A variety of processing techniques are currently employed to form the highest quality CH3NH3PbX3 films that include precursor modifications, thermal annealing and post-deposition treatments. Here we outline and discuss the resulting material qualities and device performances. Suggestions regarding needed improvements and future research directions are provided based on the current field of available literature.
TL;DR: In this article, the authors performed a life cycle assessment for two types of solution-processed perovskite solar modules to shed light on the environmental performance of this promising class of PVs.
Abstract: The past few years have witnessed a rapid evolution of perovskite solar cells, an unprecedented photovoltaic (PV) technology with both relatively low cost and high power conversion efficiency. In this paper, we perform a life cycle assessment for two types of solution-processed perovskite solar modules to shed light on the environmental performance of this promising class of PVs. One module is equipped with FTO glass, a gold cathode, and mesoporous TiO2 scaffold; the other is equipped with ITO glass, a silver cathode, and ZnO thin film. We develop comprehensive life cycle inventories (LCIs) for all components used in the modules. Based on the LCI results, we conduct life cycle impact assessment for 16 common life cycle impact indicators, Eco-indicator 99, and two sustainable indicators: the energy payback time (EPBT) and the CO2 emission factor. We compare the results of Eco-indicator 99, the EPBT, and the CO2 emission factor among existing PV technologies, and further perform uncertainty analysis and sensitivity analysis for the two modules. The results demonstrate that perovskite solar modules possess the shortest EPBT, and future research should be directed to improving the system performance ratio and the device lifetime, and reducing precious metal consumption and energy-intensive operations in order to lower the CO2 emission factor.
TL;DR: The chemical protonation of graphitic carbon nitride (CN) solids with strong oxidizing acids, for example HNO3, is demonstrated as an efficient pathway for the sol processing of a stable CN colloidal suspension, which can be translated into thin films by dip/disperse-coating techniques.
Abstract: The chemical protonation of graphitic carbon nitride (CN) solids with strong oxidizing acids, for example HNO3, is demonstrated as an efficient pathway for the sol processing of a stable CN colloidal suspension, which can be translated into thin films by dip/disperse-coating techniques. The unique features of CN colloids, such as the polymeric matrix and the reversible hydrogen bonding, result in the thin-film electrodes derived from the sol solution exhibiting a high mechanical stability with improved conductivity for charge transport, and thus show a remarkably enhanced photo-electrochemical performance. The polymer system can in principle be broadly tuned by hybridization with desired functionalities, thus paving the way for the application of CN for specific tasks, as exemplified here by coupling with carbon nanotubes.
TL;DR: In this article, a room-temperature solvent-solvent extraction (SSE) method is used for the deposition of hybrid-perovskite thin films over large areas, and its versatility in depositing high quality thin films of controlled thicknesses and various compositions (CH3NH3PbI(3−x)Brx; x = 0, 1, 2, or 3) is demonstrated.
Abstract: The room-temperature solvent–solvent extraction (SSE) concept is used for the deposition of hybrid-perovskite thin films over large areas. In this simple process, perovskite precursor solution is spin-coated onto a substrate, and instead of the conventional thermal annealing treatment, the coated substrate is immediately immersed in a bath of another solvent at room temperature. This results in efficient extraction of the precursor-solvent and induces rapid crystallization of uniform, ultra-smooth perovskite thin films. The mechanisms involved in the SSE process are studied further, and its versatility in depositing high quality thin films of controlled thicknesses (20 to 700 nm) and various compositions (CH3NH3PbI(3−x)Brx; x = 0, 1, 2, or 3) is demonstrated. Planar perovskite solar cells (PSCs) based on SSE-deposited CH3NH3PbI3 perovskite thin films deliver power conversion efficiency (PCE) up to 15.2%, and most notably an average PCE of 10.1% for PSCs with sub-100 nm semi-transparent perovskite thin films. The SSE method has generic appeal, and its key attributes—room-temperature process, rapid crystallization, large-area uniform deposition, film-thickness control, ultra-smoothness, and compositional versatility—make the SSE method potentially suitable for roll-to-roll scalable processing of hybrid-perovskite thin films for future multifunctional PSCs.
TL;DR: The discovery of methylamine induced defect-healing (MIDH) of CH3NH3PbI3 perovskite thin films based on their ultrafast, reversible chemical reaction with CH3 NH2 gas at room temperature represents a new direction in the formation of defect-free films of hybrid perovSKites.
Abstract: We report herein the discovery of methylamine (CH3NH2) induced defect-healing (MIDH) of CH3NH3PbI3 perovskite thin films based on their ultrafast (seconds), reversible chemical reaction with CH3NH2 gas at room temperature. The key to this healing behavior is the formation and spreading of an intermediate CH(3)NH(3)PbI(3)xCH(3)NH(2) liquid phase during this unusual perovskite-gas interaction. We demonstrate the versatility and scalability of the MIDH process, and show dramatic enhancement in the performance of perovskite solar cells (PSCs) with MIDH. This study represents a new direction in the formation of defect-free films of hybrid perovskites.
TL;DR: Atomic layer etching (ALE) is a technique for removing thin layers of material using sequential reaction steps that are self-limiting as mentioned in this paper, which has been studied in the laboratory for more than 25 years.
Abstract: Atomic layer etching (ALE) is a technique for removing thin layers of material using sequential reaction steps that are self-limiting. ALE has been studied in the laboratory for more than 25 years. Today, it is being driven by the semiconductor industry as an alternative to continuous etching and is viewed as an essential counterpart to atomic layer deposition. As we enter the era of atomic-scale dimensions, there is need to unify the ALE field through increased effectiveness of collaboration between academia and industry, and to help enable the transition from lab to fab. With this in mind, this article provides defining criteria for ALE, along with clarification of some of the terminology and assumptions of this field. To increase understanding of the process, the mechanistic understanding is described for the silicon ALE case study, including the advantages of plasma-assisted processing. A historical overview spanning more than 25 years is provided for silicon, as well as ALE studies on oxides, III–V compounds, and other materials. Together, these processes encompass a variety of implementations, all following the same ALE principles. While the focus is on directional etching, isotropic ALE is also included. As part of this review, the authors also address the role of power pulsing as a predecessor to ALE and examine the outlook of ALE in the manufacturing of advanced semiconductor devices.
TL;DR: A detailed overview of established precipitation and microemulsion methods for synthesizing molecularly imprinted polymer (MIP) nanoparticles (NPs) can be found in this paper.
Abstract: During the last years, artificial nanostructured materials attracted increasing scientific interest due to some remarkable properties such as high surface-to-volume ratio, low cost and straightforward preparation and handling. Among others, such materials show high potential for highly selective recognition in different fields of Analytical Chemistry, such as chemical sensor design. Carrying forward the approach of molecular imprinting from bulk/thin film to nanoparticles is one possible way to actually achieve that goal. Recent years have hence seen substantial increase in the number of MIP nanoparticle publications. This review gives a detailed overview of established precipitation and microemulsion methods for synthesising molecularly imprinted polymer (MIP) nanoparticles (NPs) as well as giving an outlook on improving those by “living” polymerisation techniques to achieve controlled geometry and thickness as well as post-synthesis functionalisation. Besides these techniques, novel solid-phase imprinting approaches have recently emerged that show high potential for automatically synthesising MIP NP and transferring the protocols to large-scale production at reduced costs. In terms of sensor application, MIP NPs lead to appreciable sensitivity and selectivity. Moreover, nano-composite materials can be tailored to include additional functionality such as magnetic and semi-conductive cores. Within optical sensors, implementation of quantum dots (QDs) as optosensing material with a MIP shell even allows for fluorescence detection of non-optically active analytes. Sensitivity can be substantially improved by introducing Surface Plasmon Resonance (SPR) and Surface-Enhanced Raman Scattering (SERS), which have recently been successfully combined with MIP NPs and are promising chemical and biological sensors. Finally, MIP NPs have also proven very useful as plastic antibodies in pseudo-immunoassays.