Growth of BaZrS3 Chalcogenide Perovskite Thin Films Without Post Annealing

Tin oxide (SnO2) as effective electron selective layer material in hybrid organic–inorganic metal halide perovskite solar cells

Layered hybrid organic–inorganic metal‐halide perovskites (HOIPs) can acquire chirality from molecules incorporated into their structure showing exciting possibilities in optoelectronics and spintronics. However, researchers have focused their attention on the study of bulk compounds, namely unstable and toxic Pb HOIPs. Herein, the chiroptical properties of R‐ and S‐β‐methylphenethylammonium Mn chloride HOIPs are reported in both the bulk and the few‐layer limit as exfoliated flakes. Red photoluminescence (PL) emission originating from the octahedrally coordinated Mn2+ is observed, with a PL shift to longer wavelengths when passing from bulk to flakes. Circular dichroism and circularly polarized PL mirrored‐signals for enantiomers are found in bulk samples, while in flakes, a degree of circularly polarized emission (P) of up to 17% at 80 K is achieved, comparable to Pb‐based HOIPs. Moreover, angle‐resolved PL measurements on flakes show that the PL emission and P are isotropic. These findings highlight the potential of these HOIPs from bulk to flakes for spin‐optoelectronic applications.

Ion migration in inorganic and hybrid organic-inorganic metal halide perovskites causes unusual phenomena in photovoltaic devices, such as current-voltage hysteresis and photoinduced phase transformations. It is now well established that metal halide perovskites are mixed ionic-electronic conductors and halide ions are mobile at room temperature. The effect of various physical stimuli like light, heat, pressure, and applied bias can affect the distribution and movement of ions. However, the impact of each stimulus is not understood as the measured response includes a combination of factors. We explore, using first-principles density functional theory (DFT), halide migration mediated by vacancies in model cubic phases of CsPbX3 (X = Cl, Br, I) and systematically control the electronic, chemical, and mechanical conditions. We assess the potential energy landscape for ion migration and how device-relevant conditions and compositional engineering can influence the physical behaviour of halide perovskites.

ConspectusOwing to the remarkable progress achieved over the past decade with research efforts from the perspectives of material synthesis, device configuration, and theoretical investigation, metal halide perovskites have emerged as a revolutionary class of light-absorbing semiconductors. The perovskite photovoltaic devices have demonstrated an impressive increase in power conversion efficiency. For single-junction perovskite solar cells, the value has risen from the initial one-digit maximum to the state-of-art record of 25.5%. Among various chemical and structural variations of perovskites, inorganic lead halides possess a more favorable operational stability and hold greater potential for perovskite/silicon tandem photovoltaics' top cells. At the initial stage of exploring all-inorganic perovskites for optoelectronic applications, many concepts, technical routes, and modification strategies were directly adopted from research on the more-developed field of organic-inorganic hybrid perovskite (OIHP). However, as understandings on inorganic perovskite deepen with research experience gained from both experimental and theoretical progression, it has been found that the difference between the asymmetric, volatile organic cations and the spherical, stable inorganic cations can lead to drastic changes on overall material properties and the subsequent device performances. In detail, the disparities reflect the crystalline and phase profiles of the material, the fabrication and passivation rationales of perovskite thin films, and the photophysics in the assembled optoelectronic devices. Therefore, the discussions of all-inorganic perovskites have their own exclusivity and are worthy of a specialized scrutinization.Here in this Account, the latest progress on the stabilization of inorganic lead halide perovskites for efficient photovoltaic applications is highlighted. A library of chemical compositions will be discussed with a focus on notable works about CsPbI3, which possesses a more favorable bandgap as a tandem to commercialized silicon solar cells. To underscore the influence of the crystal phase on the stability of inorganic perovskites, fundamental investigations regarding the chemical and physical properties, including experimental and theoretical studies, will be summarized as a means of phase control. The stability of inorganic lead halide perovskites can also be improved by the strategic introduction of external components to the light-absorbing layer, such as the incorporation of inorganic halides, organic cations, OIHPs with low dimension, etc. These strategies can synergistically improve the stability and efficiency of the fabricated devices from the perspectives of compositional tuning, dimensional engineering, surface termination, and low-dimension capping. On the basis of a careful examination and an analysis of works achieved in these categories from our group and others, we will then discuss some promising approaches toward achieving more stable and efficient photovoltaics using inorganic lead halide perovskites.

Hybrid organic-inorganic metal halide perovskite (HOIP)-based memristors have captured strong attention not only as an emerging candidate for next-generation high-density information storage technology but also for use in healthcare technology and the Internet of Things (IoT) because of their unique properties: low weight, flexibility, compatibility, stretchability, and low power consumption. In this Perspective, we review the recent advances of various aspects of flexible memristors focusing on the selection of the flexible substrates, materials, interfaces, several resistive switching mechanisms, and different methodologies of perovskite growth. The current state of the art of the memristor as an artificial synapse, light-induced resistive switching, and logic gates is comprehensively and systematically reviewed. Finally, we briefly discuss the stability factors of perovskites and present the conclusion with a broad outlook on the progress and challenges in the field of perovskite-based flexible memristors.

Tandem solar cells based on hybrid organic–inorganic metal halide perovskites have reached efficiencies up to 28%, but major concerns for long-term stability and the presence of Pb have raised inte...

Low-dimensional hybrid organic–inorganic metal halide perovskites are rapidly emerging as a fascinating sub-class of the three-dimensional parent structures, thanks to their appealing charge and thermal transport properties, paired to better chemical and thermal stabilities. Extensive investigations of the thermal behavior in these systems are of paramount relevance to understand their optoelectronic and thermoelectric applications. Herein, we present a complete thermophysical characterization of imidazolium lead iodide, (IMI)PbI3, a 1D pseudo-perovskite with chains of face-sharing octahedra, and histammonium lead iodide, (HIST)PbI4, a 2D layered perovskite with corner-sharing octahedra. Upon heating, the two compounds show highly anisotropic thermal expansion effects and high thermal stability until 250–300 °C. The thermal diffusivity of pelletized powders was measured with the laser flash technique from room temperature up to 225 °C. To account for the reduced density of the pelletized powders with respect to the bulk, the diffusivity data in different atmospheres were modeled as a function of the volume fraction and dimensionality of the pores, allowing to extrapolate the thermal conductivity of the bulk materials. The two compounds exhibit an ultralow thermal conductivity of 0.15 W/m K, two to three times lower than that reported on 3D MAPbI3 using the same technique. This finding suggests the primary role of the organic molecules within the hybrid systems, regardless of the octahedra connectivity and dimensionality.

Reactive defects in hybrid organic–inorganic metal halide perovskites that limit material functionality and durability, factors which ultimately dictate (opto)electronic device performance, are difficult to probe. Herein, we expand an electrochemical methodology for near-valence defect quantification, using a solid-state electrolyte “top contact,” to increase energy resolution and sensitivity via a differential pulse protocol. A new low level of detection of ca. 2 × 1015 cm–3 is reported for reactive defects in a triple-cation system. We confirmed that these defects are associated with mobile iodide ions in grain boundaries and at interfaces by using iodide and bromide spiked electrolytes. The detection limit for this electrochemical method is estimated to be ca. 1014 cm–3, well below that of many electrical or spectroscopic approaches. We predict this methodology lends itself to operando defect characterization during and after processing, at scale, of extremely low defect density perovskites and related optoelectronic platforms, ultimately providing an in-line approach to real-time performance and stability optimization.

Hybrid organic–inorganic metal halide perovskites have shown outstanding results to be used in various optoelectronic applications. These materials possess interesting properties such as defect tolerance, better charge separation, low recombination, higher conversion efficiency and many more. Over the period, presence of ferroelectricity has been argued to be a reason for the efficient charge separation mechanism in these systems. However, the existence of ferroelectricity in these class of materials is debated which also raises questions regarding the structure, more specifically about the polar or non-polar nature of the system. Present work, is focused on the investigation of existence/non-existence of ferroelectricity in the MAPbBr3 single crystal. Structure of this system has also been explored. For that, good quality single crystal of MAPbBr3 with rocking width of 0.12 degree have been synthesized. Two structural phase transition from orthorhombic to tetragonal and tetragonal to cubic phase has been observed at 145 K and 250 K, respectively. It has been confirmed that MAPbBr3 perovskite is not ferroelectric in any of its structural phases,with the help of temperature-dependent X-ray diffraction, dielectric permittivity measurement, P-E (Polarization versus electric field) and PUND (positive up negative down) measurements. These findings will contribute to better understanding about the structure and consequently the ferroelectric nature of these systems.

Hybrid organic–inorganic metal halide perovskites have become one of the leading thin-film semiconductors for renewable energy conversion in photovoltaics. These soft ionic materials feature remarkable optoelectronic properties and solar-to-electric power conversion efficiencies; however, they are unstable under operating conditions, such as against external environmental factors (i.e. oxygen and moisture) and internal ion migration that is accelerated upon temperature changes, voltage bias, and light. To address this challenge, various strategies have been developed to stabilise hybrid perovskite materials and their photovoltaic devices, which rely on compositional, interfacial, and device engineering. In particular, controlling their supramolecular assemblies with the organic components by tailoring various noncovalent interactions, such as hydrogen bonding, halogen bonding, van der Waals or π-based interactions, has been pertinent. This involves the use of molecular modulators that assemble at the interface with hybrid perovskites, as well as organic spacer cations templating lower-dimensional perovskite frameworks with enhanced operational stabilities. This chapter provides insights into emerging supramolecular strategies for stabilising hybrid perovskite materials and devices, advancing their applications in photovoltaics.

Aqueous phase synthesis of trimethylsulfoxonium lead triiodide for moisture-stable perovskite solar cells

Hybrid organic–inorganic metal halide perovskites have probably become the most famous and prospective class of materials for photovoltaic application in the past decade. The extremely fast increase of certified power conversion efficiencies, from 3.8 to 22.7% in less than seven years, encourages researchers around the globe and indicates the materials advantageous optoelectronic properties. The most important properties for future commercialization have turned out to be the low cost of precursor materials and the simplicity of solution processability. This article reviews the latest advancements in the solution-based sequential deposition of planar perovskite absorber layers, which show promise to be multifaceted, reproducible, and controllable. Strong research interest has recently been devoted to the optimization of the surface coverage and morphology, both of which considerably influence the photovoltaic performance. Herein, we first concentrate on the deposition of lead-containing precursors from typical polar solvents and review modifications via additive incorporation and pre-/post-treatment. Afterward, innovative methods for the conversion reaction in the usually alcoholic solvent are summarized, and the influence on the final crystal morphology is highlighted. We conclude with a short discussion about future directions and challenges.

Hybrid organic–inorganic metal halide perovskite nanocrystals (NCs) are among the candidates for color conversion materials in displays, especially in NC-based micro-light-emitting diode (micro-LED) displays. However, these NCs are still lacking long-term stability, which has hindered their large-scale applications. We mimic the working conditions, which include ultraviolet light illumination at 323 K and three different types of atmosphere (N2, vacuum, and air), respectively, to investigate the stability of CH3NH3PbBr3 NCs embedded in the polyvinylidene fluoride matrix. X-ray diffraction results indicate the generation of NH4Pb2Br5, which is produced from the encapsulated CH3NH3PbBr3 NCs in all three atmospheres, and the decomposition generates a large amount of accompanying interface defects at the surface area of NCs, resulting in the significant decrease of the photoluminescence (PL) intensity. This work highlights the stability-related mechanism of CH3NH3PbBr3 NCs under combined external stresses that mimic operating conditions. In addition, this work also suggests a new method for conducting aging tests and contributes to developing effective routes towards higher stability of perovskite NCs.

The halogen chemistry of halide perovskites

Insights on the opto-electronic structure of the inorganic mixed halide perovskites γ-CsPb(I1-xBrx)3 with low symmetry black phase