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Competing Interests: Competing interests: The authors declare no competing interests.

The stability of hybrid organic-inorganic halide perovskite semiconductors remains a significant obstacle to their application in photovoltaics. To this end, the use of low-dimensional (LD) perovskites, which incorporate hydrophobic organic moieties, provides an effective strategy to improve their stability, yet often at the expense of their performance. To address this limitation, supramolecular engineering of noncovalent interactions between organic and inorganic components has shown potential by relying on hydrogen bonding and conventional van der Waals interactions. Here, the capacity to access novel LD perovskite structures that uniquely assemble through unorthodox S-mediated interactions is explored by incorporating benzothiadiazole-based moieties. The formation of S-mediated LD structures is demonstrated, including one-dimensional (1D) and layered two-dimensional (2D) perovskite phases assembled via chalcogen bonding and S-π interactions. This involved a combination of techniques, such as single crystal and thin film X-ray diffraction, as well as solid-state NMR spectroscopy, complemented by molecular dynamics simulations, density functional theory calculations, and optoelectronic characterization, revealing superior conductivities of S-mediated LD perovskites. The resulting materials are applied in n-i-p and p-i-n perovskite solar cells, demonstrating enhancements in performance and operational stability that reveal a versatile supramolecular strategy in photovoltaics., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Hybrid halide perovskites are attractive candidates for resistive switching memories in neuromorphic computing applications due to their mixed ionic-electronic conductivity. Moreover, their exceptional optoelectronic characteristics make them effective as semiconductors in photovoltaics, opening perspectives for self-powered memory elements. These devices, however, remain unexploited, which is related to the variability in their switching characteristics, weak endurance, and retention, which limit their performance and practical use. To address this challenge, we applied low-dimensional perovskite capping layers onto 3D mixed halide perovskites using two perfluoroarene organic cations, namely (perfluorobenzyl)ammonium and (perfluoro-1,4-phenylene)dimethylammonium iodide, forming Ruddlesden-Popper and Dion-Jacobson 2D perovskite phases, respectively. The corresponding mixed-dimensional perovskite heterostructures were used to fabricate resistive switching memories based on perovskite solar cell architectures, showing that the devices based on perfluoroarene heterostructures exhibited enhanced performance and stability in inert and ambient air atmosphere. This opens perspectives for multidimensional perovskite materials in durable self-powered memory elements in the future.

Hybrid metal halide perovskites have demonstrated remarkable performances in modern photovoltaics, although their stabilities remain limited. We assess the capacity to advance their properties by relying on interfacial modulators featuring helical chirality based on P , M -(1-methylene-3-methyl-imidazolium)[6]helicene iodides. We investigate their characteristics, demonstrating comparable charge injection for enantiomers and the racemic mixture. Overall, they maintain the resulting photovoltaic performance while improving operational stability, challenging the role of helical chirality in the interfacial modulation of perovskite solar cells., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Perovskite solar cells have demonstrated exceptional development over the past decade, but their stability remains a challenge toward the application of this technology. Several strategies have been used to address this, and the use of host-guest complexation has recently attracted more interest. However, this approach has primarily been exploited in conventional perovskite solar cells based on n-i-p architectures, while its use in inverted p-i-n devices remains unexplored. Herein, we employ representative crown ether, dibenzo-24-crown-8, for interfacial host-guest complexation in inverted perovskite solar cells based on methylammonium and methylammonium-free formamidinium-cesium halide perovskite compositions. Upon post-treatment of the perovskite films, we observed nanostructures on the surface that were associated with the reduced amount of trap states at the interface with the electron transport layer. As a result, we demonstrate improved efficiencies and operational stabilities following ISOS-D-2I and ISOS-L-2I protocols, demonstrating the viability of this approach to advance device stability., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

The understanding of mixed ionic-electronic conductivity in hybrid perovskites has enabled major advances in the development of optoelectronic devices based on this class of materials. While recent investigations revealed the potential of using dimensionality effects for various applications, the implication of this strategy on mixed conductivity is yet to be established. Here, we present a systematic analysis of mixed conduction in layered (2D) hybrid halide perovskite films based on 1,4-phenylenedimethylammonium (PDMA) and benzylammonium (BzA) organic spacers in (PDMA)PbI 4 and (BzA) 2 PbI 4 compositions, forming representative Dion-Jacobson (DJ) and Ruddleson-Popper (RP) phases, respectively. Electrochemical measurements of charge transport parallel to the layered structure reveal mixed ionic-electronic conduction with electronic transport mediated by electron holes in both DJ and RP phases. In comparison to the 3D perovskites, larger activation energies for both ionic and electronic conductivities are observed which result in lower absolute values. While the layered perovskites still allow for a relatively efficient exchange of iodine with the gas phase, the lower change of conductivity on the variation of the iodine partial pressure compared with 3D perovskites is consistent with the exchange affecting only a fraction of the film, with implications for the encapsulating efficacy of these materials. We complement the analysis with a demonstration of the superior thermal stability of DJ structures compared to their RP counterparts. This can guide future explorations of dimensionality and composition to control the transport and stabilization properties of 2D perovskite films., Competing Interests: There are no conflicts to declare. Open Access funding provided by the Max Planck Society., (This journal is © The Royal Society of Chemistry.)

Artificial synapses based on resistive switching have emerged as a promising avenue for brain-inspired computing. Hybrid metal halide perovskites have provided the opportunity to simplify resistive switching device architectures due to their mixed electronic-ionic conduction, yet the instabilities under operating conditions compromise their reliability. We demonstrate reliable resistive switching and synaptic behaviour in layered benzylammonium (BzA) based halide perovskites of (BzA) 2 PbX 4 composition (X = Br, I), showing a transformation of the resistive switching from digital to analog with the change of the halide anion. While (BzA) 2 PbI 4 devices demonstrate gradual set and reset processes with reduced power consumption, the (BzA) 2 PbBr 4 system features a more abrupt switching behaviour. Moreover, the iodide-based system displays excellent retention and endurance, whereas bromide-based devices achieve a superior on/off ratio. The underlying mechanism is attributed to the migration of halide ions and the formation of halide vacancy conductive filaments. As a result, the corresponding devices emulate synaptic characteristics, demonstrating the potential for neuromorphic computing. Such resistive switching and synaptic behaviour highlight (BzA) 2 PbX 4 perovskites as promising candidates for non-volatile memory and neuromorphic computing., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Pressing global challenges, such as climate change, the COVID-19 pandemic, or antibiotic resistance, require coordinated international responses guided by evidence-informed decisions. For this purpose, it is critical that scientists engage in providing insights during the decision-making process. However, the mechanisms for the engagement of scientists in policy-making are complex and vary internationally, which often poses significant challenges to their involvement. Herein, we address some of the mechanisms and barriers for scientists to engage in policy-making with a global perspective by early-career scientists. We highlight the importance of scientific academies, societies, universities, and early-career networks as stakeholders and how they can adapt their structures to actively contribute to shaping global policies, with representative examples from chemistry-related disciplines. We showcase the importance of raising awareness, providing resources and training, and leading discussions about connecting emerging scientists with global decision-makers to address societal challenges through policies., (© 2023 Wiley-VCH Verlag GmbH.)

The industrialization of perovskite solar cells requires adequate materials and processes to make them economically viable and environmentally sustainable. Despite promising results in terms of power conversion efficiency and operational stability, several hole-transport layers currently in use still need to prove their industrial feasibility. This work demonstrates the use of nanocrystalline nickel oxide produced through flash infrared annealing (FIRA), considerably reducing the materials cost, production time, energy, and the amount of solvents required for the hole transport layer. X-ray photoelectron spectroscopy reveals a better conversion to nickel oxide and a higher oxygen-to-nickel ratio for the FIRA films as compared to control annealing methods, resulting in higher device efficiency and operational stability. Planar inverted solar cells produced with triple cation perovskite absorber result in 16.7% power conversion efficiency for 1 cm 2 devices, and 15.9% averaged over an area of 17 cm 2 ., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Dynamic crystalline materials have emerged as a unique category of condensed phase matter that combines crystalline lattice with components that display dynamic behavior in the solid state. This has involved a range of materials incorporating dynamic functional units in the form of stimuli-responsive molecular switches and machines, among others. In particular, it has been possible by relying on framework materials, such as porous molecular frameworks and other hybrid organic-inorganic systems that demonstrated potential for serving as scaffolds for dynamic molecular functions. As functional dynamics increase the level of complexity, the associated phenomena are often overlooked and need to be explored. In this perspective, we discuss a selection of recent developments of dynamic solid-state materials across material classes, outlining opportunities and fundamental and methodological challenges for their advancement toward innovative functionality and applications., (© 2023. The Author(s).)

Organic materials can tune the optical properties in layered (2D) hybrid perovskites, although their impact on photophysics is often overlooked. Here, we use transient absorption spectroscopy to probe the Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) 2D perovskite phases. We show the formation of charge transfer excitons in DJ phases, resulting in a photoinduced Stark effect which is shown to be dependent on the spacer size. By using electroabsorption spectroscopy, we quantify the strength of the photoinduced electric field, while temperature-dependent measurements demonstrate new features in the transient spectra of RP phases at low temperatures resulting from the quantum-confined Stark effect. This study reveals the impact of spacer size and perovskite phase configuration on charge transfer excitons in 2D perovskites of interest to their advanced material design.

The instability of hybrid organic-inorganic halide perovskites presents one of the pressing challenges for their application. This is associated with the sensitivity to moisture as well as mixed ionic-electronic conductivity that leads to enhanced ion migration under conditions of voltage and light bias. Some of the most effective strategies to stabilize hybrid perovskite materials during operation involve the use of interfacial molecular assemblies and low-dimensional perovskite architectures based on hydrophobic organic moieties that could suppress the effects of moisture or ion migration. For this purpose, perfluoroarenes have provided a versatile platform due to their enhanced hydrophobicity as well as the capacity to engage in various noncovalent interactions that affect the characteristics of the resulting assemblies as well as ion migration. This Perspective discusses the emerging role of perfluoroarenes in stabilizing hybrid perovskite materials and their photovoltaic devices through different modes of action, offering insights for the design of advanced materials.

Solar-to-electric energy conversion has provided one of the most powerful renewable energy technologies. In particular, hybrid organic-inorganic halide perovskites have recently emerged as leading thin-film semiconductors for new generation photovoltaics. However, their instability under operating conditions remains an obstacle to their application. To address this, we relied on supramolecular engineering in the development of organic systems that can interact with the surface of hybrid perovskites through different noncovalent interactions and enhance their operational stabilities. Moreover, we have utilized the uniquely soft yet crystalline structure of hybrid perovskites and their mixed ionic-electronic conductivity to provide a platform for advancing their functionality beyond photovoltaics. This account reviews our recent progress in supramolecular engineering of hybrid perovskites in photovoltaics and discusses their perspectives in the development of smart technologies., (Copyright 2022 Jovana V. Milic. License: This work is licensed under a Creative Commons Attribution 4.0 International License.)

During the global crisis triggered by the COVID-19 pandemic, university programs, meetings, and conferences have moved to virtual settings, with consequent erosion of mentorship opportunities for students and early-career professionals. This calls for mentorship platforms that are adapted to the new landscape in order to bring about a positive change. Our Viewpoint Article shares the perspective of the Transformative Education program and Mentorship Talks initiative at the American University of Beirut in Lebanon, with the aim of providing insights that could stimulate other mentorship platforms., (© 2022 Wiley-VCH GmbH.)

Layered hybrid perovskites are based on organic spacers separating hybrid perovskite slabs. We employ arene and perfluoroarene moieties based on 1,4-phenylenedimethylammonium (PDMA) and its perfluorinated analogue (F-PDMA) in the assembly of hybrid layered Dion-Jacobson perovskite phases. The resulting materials are investigated by X-ray diffraction, UV-vis absorption, photoluminescence, and solid-state NMR spectroscopy to demonstrate the formation of layered perovskite phases. Moreover, their behaviour was probed in humid environments to reveal nanoscale segregation of layered perovskite species based on PDMA and F-PDMA components, along with enhanced stabilities of perfluoroarene systems, which is relevant to their application.

Layered Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) hybrid perovskites are promising materials for optoelectronic applications due to their modular structure. To fully exploit their functionality, mechanical stimuli can be used to control their properties without changing the composition. However, the responsiveness of these systems to pressure compatible with practical applications (<1 GPa) remains unexploited. Hydrostatic pressure is used to investigate the structure-property relationships in representative iodide and bromide DJ and RP 2D perovskites based on 1,4-phenylenedimethylammonium (PDMA) and benzylammonium (BzA) spacers in the 0-0.35 GPa pressure range. Pressure-dependent X-ray scattering measurements reveal that lattices of these compositions monotonically shrink and density functional theory calculations provide insights into the structural changes within the organic spacer layer. These structural changes affect the optical properties; the most significant shift in the optical absorption is observed in (BzA) 2 PbBr 4 under 0.35 GPa pressure, which is attributed to an isostructural phase transition. Surprisingly, the RP and DJ perovskites behave similarly under pressure, despite the different binding modes of the spacer molecules. This study provides important insights into how the manipulation of the crystal structure affects the optoelectronic properties of such materials, whereas the reversibility of their response expands the perspectives for future applications., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Dion-Jacobson (DJ) iodoplumbates based on 1,4-phenylenedimethanammonium (PDMA) have recently emerged as promising light absorbers for perovskite solar cells. While PDMA is one of the simplest aromatic spacers potentially capable of forming a DJ structure based on (PDMA)A n -1 Pb n I 3 n +1 composition, the crystallographic proof has not been reported so far. Single crystal structure of a DJ phase based on PDMA is presented and high-field solid-state NMR spectroscopy is used to characterize the structure of PDMA-based iodoplumbates prepared as thin films and bulk microcrystalline powders. It is shown that their atomic-level structure does not depend on the method of synthesis and that it is ordered and similar for all iodoplumbate homologues. Moreover, the presence of lower (n) homologues in thin films is identified through UV-Vis spectroscopy, photoluminescence spectroscopy, and X-ray diffraction measurements, complemented by cathodoluminescence mapping. A closer look using cathodoluminescence shows that the micron-scale microstructure corresponds to a mixture of different layered homologues that are well distributed throughout the film and the presence of layer edge states which dominate the emission. This work therefore determines the formation of DJ phases based on PDMA as the spacer cation and reveals their properties on a multi-length scale, which is relevant for their application in optoelectronics., (© 2021 The Authors. Small published by Wiley-VCH GmbH.)

Layered hybrid perovskites based on Dion-Jacobson phases are of interest to various optoelectronic applications. However, the understanding of their structure-property relationships remains limited. Here, we present a systematic study of Dion-Jacobson perovskites based on (S)PbX 4 ( n = 1) compositions incorporating phenylene-derived aromatic spacers (S) with different anchoring alkylammonium groups and halides (X = I, Br). We focus our study on 1,4-phenylenediammonium (PDA), 1,4-phenylenedimethylammonium (PDMA), and 1,4-phenylenediethylammonium (PDEA) spacers. Systems based on PDA did not form a well-defined layered structure, showing the formation of a 1D structure instead, whereas the extension of the alkyl chains to PDMA and PDEA rendered them compatible with the formation of a layered structure, as shown by X-ray diffraction and solid-state NMR spectroscopy. In addition, the control of the spacer length affects optical properties and environmental stability, which is enhanced for longer alkyl chains and bromide compositions. This provides insights into their design for optoelectronic applications.

ConspectusHybrid halide perovskite materials have become one of the leading candidates for various optoelectronic applications. They are based on organic-inorganic structures defined by the AMX 3 composition, were A is the central cation that can be either organic (e.g., methylammonium, formamidinium (FA)) or inorganic (e.g., Cs + ), M is a divalent metal ion (e.g., Pb 2+ or Sn 2+ ), and X is a halide anion (I - , Br - , or Cl - ). In particular, FAPbI 3 perovskites have shown remarkable optoelectronic properties and thermal stabilities. However, the photoactive α-FAPbI 3 (black) perovskite phase is not thermodynamically stable at ambient temperature and forms the δ-FAPbI 3 (yellow) phase that is not suitable for optoelectronic applications. This has stimulated intense research efforts to stabilize and realize the potential of the α-FAPbI 3 perovskite phase. In addition, hybrid perovskites were proven to be unstable against the external environmental conditions (air and moisture) and under device operating conditions (voltage and light), which is related to various degradation mechanisms. One of the strategies to overcome these instabilities has been based on low-dimensional hybrid perovskite materials, in particular layered two-dimensional (2D) perovskite phases composed of organic layers separating hybrid perovskite slabs, which were found to be more stable toward ambient conditions and ion migration. These materials are mostly based on S x A n -1 Pb n X 3 n +1 composition with various mono- ( x = 1) or bifunctional ( x = 2) organic spacer cations that template hybrid perovskite slabs and commonly form either Ruddlesden-Popper (RP) or Dion-Jacobson (DJ) phases. These materials behave as natural quantum wells since charge carriers are confined to the inorganic slabs, featuring a gradual decrease in the band gap as the number of inorganic layers ( n ) increases from n = 1 (2D) to n = ∞ (3D). While various layered 2D perovskites have been developed, their FA-based analogues remain under-represented to date. Over the past few years, several research advances enabled the realization of FA-based layered perovskites, which have also demonstrated a unique templating effect in stabilizing the α-FAPbI 3 phase. This, for instance, involved the archetypical n -butylammonium and 2-phenylethylammonium organic spacers as well as guanidinium, 5-ammonium valeric acid, iso -butylammonium, benzylammonium, n -pentylammonium, 2-thiophenemethylammonium, 2-(perfluorophenyl)ethylammonium, 1-adamantylmethanammonium, and 1,4-phenylenedimethanammonium. FAPbBr 3 -based layered perovskites have also demonstrated potential in various optoelectronic applications, yet the opportunities associated with FAPbI 3 -based perovskites have attracted particular attention in photovoltaics, stimulating further developments. This Account provides an overview of some of these recent developments, with a particular focus on FAPbI 3 -based layered perovskites and their utility in photovoltaics, while outlining challenges and opportunities for these hybrid materials in the future.

Formamidinium lead iodide perovskites are promising light-harvesting materials, yet stabilizing them under operating conditions without compromising optimal optoelectronic properties remains challenging. We report a multimodal host-guest complexation strategy to overcome this challenge using a crown ether, dibenzo-21-crown-7, which acts as a vehicle that assembles at the interface and delivers Cs + ions into the interior while modulating the material. This provides a local gradient of doping at the nanoscale that assists in photoinduced charge separation while passivating surface and bulk defects, stabilizing the perovskite phase through a synergistic effect of the host, guest, and host-guest complex. The resulting solar cells show power conversion efficiencies exceeding 24% and enhanced operational stability, maintaining over 95% of their performance without encapsulation for 500 h under continuous operation. Moreover, the host contributes to binding lead ions, reducing their environmental impact. This supramolecular strategy illustrates the broad implications of host-guest chemistry in photovoltaics.

Global societal challenges emphasize the importance of collaboration between scientists and policy-makers, while the participation of a diverse group of professionals, including early-career scientists, is critical towards a sustainable future. The European Young Chemists' Network (EYCN) has been actively working with the European Chemical Society (EuChemS) to create a platform for early-career chemists in policy advice. This article comments on the possible roles of scientists in policy-making and provides an overview of relevant initiatives and platforms at the European level that could facilitate involvement. Opportunities for participation in policy advice from the perspective of early-career chemists are discussed and examples of impact are provided, hoping to stimulate further discussions and engagement in policy-making., (© 2021 Wiley-VCH GmbH.)

The use of layered perovskites is an important strategy to improve the stability of hybrid perovskite materials and their optoelectronic devices. However, tailoring their properties requires accurate structure determination at the atomic scale, which is a challenge for conventional diffraction-based techniques. We demonstrate the use of nuclear magnetic resonance (NMR) crystallography in determining the structure of layered hybrid perovskites for a mixed-spacer model composed of 2-phenylethylammonium (PEA + ) and 2-(perfluorophenyl)ethylammonium (FEA + ) moieties, revealing nanoscale phase segregation. Moreover, we illustrate the application of this structure in perovskite solar cells with power conversion efficiencies that exceed 21%, accompanied by enhanced operational stability.

The use of molecular modulators to reduce the defect density at the surface and grain boundaries of perovskite materials has been demonstrated to be an effective approach to enhance the photovoltaic performance and device stability of perovskite solar cells. Herein, we employ crown ethers to modulate perovskite films, affording passivation of undercoordinated surface defects. This interaction has been elucidated by solid-state nuclear magnetic resonance and density functional theory calculations. The crown ether hosts induce the formation of host-guest complexes on the surface of the perovskite films, which reduces the concentration of surface electronic defects and suppresses nonradiative recombination by 40%, while minimizing moisture permeation. As a result, we achieved substantially improved photovoltaic performance with power conversion efficiencies exceeding 23%, accompanied by enhanced stability under ambient and operational conditions. This work opens a new avenue to improve the performance and stability of perovskite-based optoelectronic devices through supramolecular chemistry.

Formamidinium (FA) lead iodide perovskite materials feature promising photovoltaic performances and superior thermal stabilities. However, conversion of the perovskite α-FAPbI 3 phase to the thermodynamically stable yet photovoltaically inactive δ-FAPbI 3 phase compromises the photovoltaic performance. A strategy is presented to address this challenge by using low-dimensional hybrid perovskite materials comprising guaninium (G) organic spacer layers that act as stabilizers of the three-dimensional α-FAPbI 3 phase. The underlying mode of interaction at the atomic level is unraveled by means of solid-state nuclear magnetic resonance spectroscopy, X-ray crystallography, transmission electron microscopy, molecular dynamics simulations, and DFT calculations. Low-dimensional-phase-containing hybrid FAPbI 3 perovskite solar cells are obtained with improved performance and enhanced long-term stability., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

There has been an ongoing effort to overcome the limitations associated with the stability of hybrid organic-inorganic perovskite solar cells by using different organic agents as additives to the perovskite formulations. The functionality of organic additives has been predominantly limited to exploiting hydrogen-bonding interactions, while the relevant atomic-level binding modes remain elusive. Herein, we introduce a bifunctional supramolecular modulator, 1,2,4,5-tetrafluoro-3,6-diiodobenzene, which interacts with the surface of the triple-cation double-halide perovskite material via halogen bonding. We elucidate its binding mode using two-dimensional solid-state 19 F NMR spectroscopy in conjunction with density functional theory calculations. As a result, we demonstrate a stability enhancement of the perovskite solar cells upon supramolecular modulation, without compromising the photovoltaic performances.

Chemical doping of inorganic-organic hybrid perovskites is an effective way of improving the performance and operational stability of perovskite solar cells (PSCs). Here we use 5-ammonium valeric acid iodide (AVAI) to chemically stabilize the structure of α-FAPbI 3 . Using solid-state MAS NMR, we demonstrate the atomic-level interaction between the molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find that one-step deposition of the perovskite in the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. As a result, we achieve greatly enhanced solar cell performance for the optimized AVA-based devices with a maximum power conversion efficiency (PCE) of 18.94%. The devices retain 90% of the initial efficiency after 300 h under continuous white light illumination and maximum-power point-tracking measurement.

The quest for nanoscale molecular machines has inspired the search for their close relatives, molecular grippers. This path was paved by the development of resorcin[4]arene cavitands and their quinone-based redox-active congeners. In this Concept article, the efforts to design and establish the control of quinone-functionalized resorcin[4]arenes by electronic and electromagnetic stimuli is described. This was achieved by relying on paramagnetic semiquinone radical anions formed electrochemically or by photoredox catalysis. The gripper-like motion of such species could not be studied by conventional NMR spectroscopy. Instead, an entirely different approach had to be developed that included various electroanalytical and spectroelectrochemical methods, including UV/Vis/NIR spectroelectrochemistry, pulsed EPR and Davies 1 H ENDOR spectroscopy, transient absorption spectroscopy, and time-resolved luminescence measurements, besides density functional theory calculations and X-ray crystallography. The conceptual breakthroughs are reviewed as well as the current state and future perspectives of photoredox-switchable molecular grippers., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Preventing the degradation of metal perovskite solar cells (PSCs) by humid air poses a substantial challenge for their future deployment. We introduce here a two-dimensional (2D) A 2 PbI 4 perovskite layer using pentafluorophenylethylammonium (FEA) as a fluoroarene cation inserted between the 3D light-harvesting perovskite film and the hole-transporting material (HTM). The perfluorinated benzene moiety confers an ultrahydrophobic character to the spacer layer, protecting the perovskite light-harvesting material from ambient moisture while mitigating ionic diffusion in the device. Unsealed 3D/2D PSCs retain 90% of their efficiency during photovoltaic operation for 1000 hours in humid air under simulated sunlight. Remarkably, the 2D layer also enhances interfacial hole extraction, suppressing nonradiative carrier recombination and enabling a power conversion efficiency (PCE) >22%, the highest reported for 3D/2D architectures. Our new approach provides water- and heat-resistant operationally stable PSCs with a record-level PCE.

Hybrid organic-inorganic perovskites have become one of the leading thin-film semiconductors for optoelectronics. Their broad application will greatly depend on overcoming the key obstacles associated with poor stability and limited scalability. There has been an ongoing effort to diminish some of these limitations by using organic additives. However, considering the lack of understanding of the underlying structure-property relationships, this progress was greatly based on trial and error as molecular-level design remains challenging. Our approach for enhancing the stability of hybrid perovskites without compromising their efficiency is based on judicious molecular design of multifunctional molecular modulators through fine-tuning of noncovalent interactions and exploiting their structural adaptability. The design principles were scrutinized by solid-state NMR spectroscopy to unravel a new path for stable and scalable perovskite solar cells, which we review in this article.

Three-dimensional (3D) perovskite materials display remarkable potential in photovoltaics owing to their superior solar-to-electric power conversion efficiency, with current efforts focused on improving stability. Two-dimensional (2D) perovskite analogues feature greater stability toward environmental factors, such as moisture, owing to a hydrophobic organic cation that acts as a spacer between the inorganic layers, which offers a significant advantage over their comparatively less stable 3D analogues. Here, we demonstrate the first example of a formamidinium (FA) containing Dion-Jacobson 2D perovskite material characterized by the BFA n-1 Pb n I 3 n+1 formulation through employing a novel bifunctional organic spacer (B), namely 1,4-phenylenedimethanammonium (PDMA). We achieve remarkable efficiencies exceeding 7% for (PDMA)FA 2 Pb 3 I 10 based 2D perovskite solar cells resisting degradation when exposed to humid ambient air, which opens up new avenues in the design of stable perovskite materials.

Chalcogen bonding (CB) is the focus of increased attention for its applications in medicinal chemistry, materials science, and crystal engineering. However, the origin of sulfur's recognition properties remains controversial, and experimental evidence for supporting theories is still emerging. Here, a comprehensive evaluation of sulfur CB interactions is presented by investigating 2,1,3-benzothiadiazole X-ray crystallographic structures gathered from the Cambridge Structure Database (CSD), Protein Data Bank (PDB), and own laboratory findings. Through the systematic analysis of substituent effects on a subset library of over thirty benzothiadiazole derivatives, the competing interactions have been categorized into four main classes, namely 2S-2N CB square, halogen bonding (XB), S⋅⋅⋅S, and hydrogen-bonding (HB). A geometric model is employed to characterize the 2S-2N CB square motifs and discuss the role of electrostatic, dipole, and orbital contributions toward the interaction., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Perovskite solar cells present one of the most prominent photovoltaic technologies, yet their stability, scalability, and engineering at the molecular level remain challenging. We demonstrate a concept of multifunctional molecular modulation of scalable and operationally stable perovskite solar cells that exhibit exceptional solar-to-electric power conversion efficiencies. The judiciously designed bifunctional molecular modulator SN links the mercapto-tetrazolium (S) and phenylammonium (N) moieties, which passivate the surface defects, while displaying a structure-directing function through interaction with the perovskite that induces the formation of large grain crystals of high electronic quality of the most thermally stable formamidinium cesium mixed lead iodide perovskite formulation. As a result, we achieve greatly enhanced solar cell performance with efficiencies exceeding 20% for active device areas above 1 cm 2 without the use of antisolvents, accompanied by outstanding operational stability under ambient conditions.