Surface passivated halide perovskite single-crystal for efficient photoelectrochemical synthesis of dimethoxydihydrofuran

Flexible Single-Crystal Perovskite Photodetectors via Polymer-Controlled Transfer

The large-sized perovskite single-crystal sheet (SCS) serves as the ideal research platform for perovskite photodetectors due to its outstanding carrier photophysics, pronounced geometric aspect ratio, and ultrahigh material utilization rate. However, its performance in flexible device applications is relatively lackluster due to the rigid and brittle nature of the three-dimensional cubic lattices. In this work, the indium tin oxide (ITO)-based multimillimeter-sized MAPbBr3 SCS is transformed into MAPbI3 SCS via ion exchange strategy. Significantly, we proposed and implemented a polymer-controlled transfer strategy─utilizing the dichloromethane (DCM) solution of poly(methyl methacrylate) (PMMA)─to nondestructively transfer the whole perovskite SCS off the ITO substrates and subsequently adhere it onto a flexible polyethylene terephthalate (PET) substrate of interdigital electrode, thereby fabricating a lateral-structured photodetector with a PMMA-SCS-Au-PET multilayer configuration. The tight self-encapsulation between the top PMMA membrane and the bottom PET substrate imparts excellent waterproof stability and concurrently excellent mechanical flexibility to these devices; additionally, the MAPbI3 device exhibits comprehensively superior performance to the MAPbBr3 one. This work represents a proactive attempt and exploration of the high-performance advancement of large-sized SCS photodetectors, undoubtedly introducing novel momentum and solutions to this domain.

Orthogonal Electrochemical Stability of Bulk and Surface in Lead Halide Perovskite Thin Films and Nanocrystals

Lead halide perovskites have attracted significant attention for their wide-ranging applications in optoelectronic devices. A ubiquitous element in these applications is that charging of the perovskite is involved, which can trigger electrochemical degradation reactions. Understanding the underlying factors governing these degradation processes is crucial for improving the stability of perovskite-based devices. For bulk semiconductors, the electrochemical decomposition potentials depend on the stabilization of atoms in the lattice-a parameter linked to the material's solubility. For perovskite nanocrystals (NCs), electrochemical surface reactions are strongly influenced by the binding equilibrium of passivating ligands. Here, we report a spectro-electrochemical study on CsPbBr3 NCs and bulk thin films in contact with various electrolytes, aimed at understanding the factors that control cathodic degradation. These measurements reveal that the cathodic decomposition of NCs is primarily determined by the solubility of surface ligands, with diminished cathodic degradation for NCs in high-polarity electrolyte solvents where ligand solubilities are lower. However, the solubility of the surface ligands and bulk lattice of NCs are orthogonal, such that no electrolyte could be identified where both the surface and bulk are stabilized against cathodic decomposition. This poses inherent challenges for electrochemical applications: (i) The electrochemical stability window of CsPbBr3 NCs is constrained by the reduction potential of dissolved Pb2+ complexes, and (ii) cathodic decomposition occurs well before the conduction band can be populated with electrons. Our findings provide insights to enhance the electrochemical stability of perovskite thin films and NCs, emphasizing the importance of a combined selection of surface passivation and electrolyte.

Photoelectrochemical Ni-catalyzed cross-coupling of aryl bromides with amine at ultra-low potential

Photoelectrochemical (PEC) cell is an ideal platform for organic transformation because of its green benefits and minimal energy consumption. As an emerging methodology, the reaction types of photoelectrocatalytic organic synthesis (PECOS) are limited to simple oxidation and C-H activation at current stage. Metal catalysis for the construction of C(sp2)-N bonds has not been touched yet in PECOS. We introduce here a PEC method that successfully engages Ni catalysis for the mild production of aniline derivatives. Experimental and computational investigations elucidate that the addition of photoanode-generated amine radical to Ni catalyst avoids the sluggish nucleophilic attack, enabling the reaction to proceed at an ultra-low potential (-0.4 V vs. Ag/AgNO3) and preventing the overoxidation of products in conventional electrochemical synthesis. This synergistic catalysis strategy exhibits good functional group tolerance and wide substrate scope on both aryl halides and amines, by which some important natural products and pharmaceutical chemicals have been successfully modified.

Multifunctional Buffer Layer Engineering for Efficient and Stable Wide-Bandgap Perovskite and Perovskite/Silicon Tandem Solar Cells

Inverted perovskite solar cells (PSCs) are preferred for tandem applications due to their superior compatibility with diverse bottom solar cells. However, the solution processing and low formation energy of perovskites inevitably lead to numerous defects at both the bulk and interfaces. We report a facile and effective strategy for precisely modulating the perovskite by incorporating AlOx deposited by atomic layer deposition (ALD) on the top interface. We find that Al3+ can not only infiltrate the bulk phase and interact with halide ions to suppress ion migration and phase separation but also regulate the arrangement of energy levels and passivate defects on the perovskite surface and grain boundaries. Additionally, ALD-AlOx exhibits an encapsulation effect through a dense interlayer. Consequently, the ALD-AlOx treatment can significantly improve the power conversion efficiency (PCE) to 21.80 % for 1.66 electron volt (eV) PSCs. A monolithic perovskite-silicon TSCs using AlOx-modified perovskite achieved a PCE of 28.5 % with excellent photothermal stability. More importantly, the resulting 1.55 eV PSC and module achieved a PCE of 25.08 % (0.04 cm2) and 21.01 % (aperture area of 15.5 cm2), respectively. Our study provides an effective way to efficient and stable wide-band gap perovskite for perovskite-silicon TSCs and paves the way for large-area inverted PSCs.

Full-color fiber light-emitting diodes based on perovskite quantum wires

Fiber light-emitting diodes (Fi-LEDs), which can be used for wearable lighting and display devices, are one of the key components for fiber/textile electronics. However, there exist a number of impediments to overcome on device fabrication with fiber-like substrates, as well as on device encapsulations. Here, we uniformly grew all-inorganic perovskite quantum wire arrays by filling high-density alumina nanopores on the surface of Al fibers with a dip-coating process. With a two-step evaporation method to coat a surrounding transporting layer and semitransparent electrode, we successfully fabricated full-color Fi-LEDs with emission peaks at 625 nanometers (red), 512 nanometers (green), and 490 nanometers (sky-blue), respectively. Intriguingly, additional polydimethylsiloxane packaging helps instill the mechanical bendability, stretchability, and waterproof feature of Fi-LEDs. The plasticity of Al fiber also allows the one-dimensional architecture Fi-LED to be shaped and constructed for two-dimensional or even three-dimensional architectures, opening up a new vista for advanced lighting with unconventional formfactors.

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Surface Engineering of Perovskite Single Crystals by Atomic Layer Deposited Tin Oxide for Optical Communication

Perovskite single crystals with excellent physical properties have broad prospects in the field of optoelectronics. However, the presence of dangling bonds, surface dislocations, and chemical impurities results in high surface defect density and sensitivity to humidity. Unfortunately, there are relatively few surface engineering strategies for single perovskite single crystals. We present a strategy utilizing atomic layer deposited SnOx to passivate surface defects in perovskite single crystals. The photodetector prepared based on the modified FAPbBr3 single crystals exhibits a low dark current of 1.89 × 10-9 A at a 5 V bias, close to 4 times lower with respect to the pristine device, a high detectivity of 2.3 × 1010 jones, and a fast response time of 27 μs. Moreover, the photodetectors feature long-term operational stability because the presence of a dense SnOx capping layer hinders the ingress of moisture and diffusion of ions. We further demonstrate the promise of our perovskite single crystal detectors for real-time subaqueous optical communication.

A controlled non-radical chlorine activation pathway on hematite photoanodes for efficient oxidative chlorination reactions

Photo(electro)catalytic chlorine oxidation has emerged as a useful method for chemical transformation and environmental remediation. However, the reaction selectivity usually remains low due to the high activity and non-selectivity characteristics of free chlorine radicals. In this study, we report a photoelectrochemical (PEC) strategy for achieving controlled non-radical chlorine activation on hematite (α-Fe2O3) photoanodes. High selectivity (up to 99%) and faradaic efficiency (up to 90%) are achieved for the chlorination of a wide range of aromatic compounds and alkenes by using NaCl as the chlorine source, which is distinct from conventional TiO2 photoanodes. A comprehensive PEC study verifies a non-radical "Cl+" formation pathway, which is facilitated by the accumulation of surface-trapped holes on α-Fe2O3 surfaces. The new understanding of the non-radical Cl- activation by semiconductor photoelectrochemistry is expected to provide guidance for conducting selective chlorine atom transfer reactions.

Highly Selective Tandem Photoelectrochemical C-H Activation via Bromine Evolution Reaction in Two-Phase Electrolyte

The development of environmentally friendly and safe chemical processes using renewable energy sources is important. In this study, a photoelectrochemical (PEC) cell was used for the tandem bromination of sp3 carbon within a unique two-phase electrolyte system. By incorporation of a RuOx cocatalyst, the Ta3N5 photoelectrode demonstrated a remarkable selectivity for Br2 close to 100%. The kinetic study for charge carriers of photoelectrodes reveals that the improved charge transfer at Ta3N5/RuOx interfaces contributed to excellent photoelectrochemical Br2 evolution activity. The photoelectrochemically produced Br2 was utilized for bromination of α-sp3 carbon in toluene, 1-methylnaphthalene, ethylbenzene, or cyclohexane by the Ta3N5/RuOx photoanode with 100% regioselectivity. The coupling of the Ta3N5 photoanode and InP photocathode generated H2 and Br2 under light illumination without external bias. This study provides systematic insights into the design of photoelectrodes for solar-driven tandem bromination systems within the unique environment of a two-phase electrolyte system.

Al2 O3 -coated BiVO4 Photoanodes for Photoelectrocatalytic Regioselective C-H Activation of Aromatic Amines

Photoelectrochemistry is becoming an innovative approach to organic synthesis. Generally, the current photoelectrocatalytic organic transformations suffer from limited reaction type, low conversion efficiency and poor stability. Herein, we develop efficient and stable photoelectrode materials using metal oxide protective layer, with a focus on achieving regioselective activation of amine compounds. Notably, our photoelectrochemistry process is implemented under mild reaction conditions and does not involve any directing groups, transition metals or oxidants. The results demonstrate that beyond photocatalysis and electrocatalysis, photoelectrocatalysis exhibits high efficiency, remarkable repeatability and good functional group tolerance, highlighting its great potential for applications.

A Perovskite Photovoltaic Mini-Module-CsPbBr3 Photoelectrochemical Cell Tandem Device for Solar-Driven Degradation of Organic Compounds

Recently, halide perovskites have been widely explored for high-efficiency photocatalysis or photoelectrochemical (PEC) cells. Here, in order to make an efficient photoanode electrode for the degradation of pollutants, concretely 2-mercaptobenzothiazole (MBT), nanoscale cesium lead bromide (CsPbBr3) perovskite was directly formed on the surface of mesoporous titanium dioxide (meso-TiO2) film using a two-step spin-coating process. This photoelectrode recorded a photocurrent of up to 3.02 ± 0.03 mA/cm2 under standard AM 1.5G (100 mW/cm2) illumination through an optimization process such as introducing a thin aluminum oxide (Al2O3) coating layer. Furthermore, to supply high voltage for efficient oxidation of MBT without an external bias, we developed a new photovoltaic/PEC tandem system using a methylammonium lead iodide (MAPbI3) based mini-module consisting of three solar cells interconnected in series and confirmed its successful operation. This approach looks very promising due to its applicability to various PEC reactions.

High-efficiency, flexible and large-area red/green/blue all-inorganic metal halide perovskite quantum wires-based light-emitting diodes

Metal halide perovskites have shown great promise as a potential candidate for next-generation solid state lighting and display technologies. However, a generic organic ligand-free and antisolvent-free solution method to fabricate highly efficient full-color perovskite light-emitting diodes has not been realized. Herein, by utilizing porous alumina membranes with ultra-small pore size as templates, we have successfully fabricated crystalline all-inorganic perovskite quantum wire arrays with ultrahigh density and excellent uniformity, using a generic organic ligand-free and anti-solvent-free solution method. The quantum confinement effect, in conjunction with the high light out-coupling efficiency, results in high photoluminescence quantum yield for blue, sky-blue, green and pure-red perovskite quantum wires arrays. Consequently, blue, sky-blue, green and pure-red LED devices with spectrally stable electroluminescence have been successfully fabricated, demonstrating external quantum efficiencies of 12.41%, 16.49%, 26.09% and 9.97%, respectively, after introducing a dual-functional small molecule, which serves as surface passivation and hole transporting layer, and a halide vacancy healing agent.

Combining π-Conjugation and Cation-π Interaction for Water-Stable and Photoconductive One-Dimensional Hybrid Lead Bromide

Hybrid lead halide perovskites and their derivatives are important optoelectronic materials but suffer from water instability. Combining both the optoelectronics and the water stability of such systems is a major challenge in material design today. To address this issue, we employ the well-known π-conjugation and cation-π interaction concepts in designing a hybrid lead halide perovskite derivative system. (4,4'-VDP)Pb₂Br₆ (VDP = vinylenedipyridinium) single crystals are prepared. They have a one-dimensional (1D) arrangement of inorganic Pb-Br sublattices connected via the 4,4'-VDP organic sublattice. The π-conjugation in the 4,4'-VDP sublattice allows electronic communication between the 1D Pb-Br units, reducing the band gap and improving the photoconductivity. Importantly, N⁺ of one 4,4'-VDP molecular ion interacts with the π-electron cloud of the adjacent one. This intermolecular cation-π interaction extends throughout the organic sublattice, making the hybrid crystal stable when stored under water for more than a year without requiring any encapsulations.

Subsurface Engineering Induced Fermi Level De-pinning in Metal Oxide Semiconductors for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-O_v ) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-O_v were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated O_v located at sub ∼2-5 nm region. Mott-Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm^-2 at 1.23 V vs. RHE were achieved on BiVO₄ , Bi₂ O₃ , TiO₂ with outstanding stability for 72 h, outperforming most reported works under the identical conditions.

Charge transport dynamics of a C6H4NH2CuBr2I/TiO2 heterojunction in aqueous solution under reverse bias

The photocurrent output of the C₆H₄NH₂CuBr₂I/TiO₂ heterojunction photoelectrode in an aqueous solution is super stable even after 30 000 s. However, the photocurrent is extremely weak. Intensity-modulated photocurrent spectroscopy revealed that the electron transfer in the C₆H₄NH₂CuBr₂I/TiO₂ photoelectrode without bias is not sufficiently fast to compete with the charge recombination process due to the short diffusion length (∼23 nm), resulting in a low photocurrent. The charge separation and charge transfer efficiency in the bulk of C₆H₄NH₂CuBr₂I could be significantly improved under a small reverse electric field (E_r), resulting in an enhanced photocurrent.

Activating C-H Bonds by Tuning Fe Sites and an Interfacial Effect for Enhanced Methanol Oxidation

The interaction mechanism between the reacting species and the active site of α-Fe₂ O₃ -based photoanodes in photoelectrochemical methanol conversion reaction is still ambiguous. Herein, a simple two-step strategy is demonstrated to fabricate a porous α-Fe₂ O₃ /CoFe₂ O₄ heterojunction for the methanol conversion reaction. The influence of the electronic structure of active site and interfacial effect on the reaction are investigated by constructing two different FeO₆ octahedral configurations and heterogeneous structures. The optimal sample ZnFeCo-2 affords high photocurrent density of 1.17 mA cm^-2 at 0.5 V vs Ag/AgCl, which is 3.2 times than that of ZnFe (0.37 mA cm^-2 ). Meanwhile, the ZnFeCo-2 also exhibits 97.8% Faraday efficiency of CH₃ OH to HCHO, and long-term stability over 40 h. Furthermore, density functional theory calculations reveal that the heterostructured α-Fe₂ O₃ /CoFe₂ O₄ with favorable electron transfer effectively lowers methanol adsorption, C-H bond activation, and HCHO desorption energy relative to the pristine α-Fe₂ O₃ , resulting in excellent methanol conversion efficiency.

A universal all-solid synthesis for high throughput production of halide perovskite

Halide perovskites show ubiquitous presences in growing fields at both fundamental and applied levels. Discovery, investigation, and application of innovative perovskites are heavily dependent on the synthetic methodology in terms of time-/yield-/effort-/energy- efficiency. Conventional wet chemistry method provides the easiness for growing thin film samples, but represents as an inefficient way for bulk crystal synthesis. To overcome these, here we report a universal solid state-based route for synthesizing high-quality perovskites, by means of simultaneously applying both electric and mechanical stress fields during the synthesis, i.e., the electrical and mechanical field-assisted sintering technique. We employ various perovskite compositions and arbitrary geometric designs for demonstration in this report, and establish such synthetic route with uniqueness of ultrahigh yield, fast processing and solvent-free nature, along with bulk products of exceptional quality approaching to single crystals. We exemplify the applications of the as-synthesized perovskites in photodetection and thermoelectric as well as other potentials to open extra chapters for future technical development.

Lewis Base Plays a Double-Edged-Sword Role in Trap State Engineering of Perovskite Polycrystals

We report the double-edged-sword effect of the thiourea (a typical Lewis base) additive for tailoring the trap state distribution of perovskite polycrystalline films. Through the thiourea treatment, the polycrystal grain size is greatly increased because of the reduced crystallization activation energy, which, together with the surface defect passivation, alters the density of the energetically "deep" and "shallow" trap states in a trade-off manner. Based on this finding and further photoelectric and spectral studies, the nonmonotonic dependence of the photoluminescence intensity on the thiourea concentration and the complicated time-resolved photoluminescence behavior are excellently clarified. As a proof of concept, the photophysical performance of perovskite polycrystals is optimized via a modified Lewis base treatment by taking the proposed double-edged-sword effect into account.

Metal Halide Perovskites for Solar Fuel Production and Photoreactions

Photocatalysis is an easily configurable and cost-effective technology for the conversion of solar energy into chemical energy. Recently, increasing attention has been given to metal halide perovskite (MHP) photocatalysts because of the development of stabilization strategies for MHPs under reaction conditions. From this perspective, we first describe several substantial breakthroughs in the photocatalytic application of MHPs. Performance trends in the solar fuel production applications of MHPs, including photocatalytic H₂ generation and photocatalytic CO₂ reduction reactions, are then described. Recent developments to extend the use of MHPs to various photocatalytic organic transformations are also highlighted. Finally, we propose several scientific challenges for the practical implications of MHPs for solar fuel production and various photoreactions.

Introducing Intermolecular Cation-π Interactions for Water-Stable Low Dimensional Hybrid Lead Halide Perovskites

Optoelectronically active hybrid lead halide perovskites dissociate in water. To prevent this dissociation, here, we introduce long-range intermolecular cation-π interactions between A-site cations of hybrid perovskites. An aromatic diamine like 4,4'-trimethylenedipyridine, if protonated, can show a long-range cation-π stacking, and therefore, serves as our A-site cation. Consequently, 4,4'-trimethylenedipyridinium lead bromide [(4,4'-TMDP)Pb₂ Br₆ ], a one-dimensional hybrid perovskite, remains completely stable after continuous water treatment for six months. Mechanistic insights about the cation-π interactions are obtained by single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy. The concept of long-range cation-π interaction is further extended to another A-site cation 4,4'-ethylenedipyridinium ion (4,4'-EDP), forming water-stable (4,4'-EDP)Pb₂ Br₆ perovskite. These water-stable perovskites are then used to fabricate white light-emitting diode and for light up-conversion through tunable third-harmonic generation. Note that the achieved water stability is the intrinsic stability of perovskite composition, unlike the prior approach of encapsulating the unstable perovskite material (or device) by water-resistant materials. The introduced cation-π interactions can be a breakthrough strategy in designing many more compositions of water-stable low-dimensional hybrid perovskites.

Limits to Electrical Mobility in Lead-Halide Perovskite Semiconductors

Semiconducting polycrystalline thin films are cheap to produce and can be deposited on flexible substrates, yet high-performance electronic devices usually utilize single-crystal semiconductors, owing to their superior charge-carrier mobilities and longer diffusion lengths. Here we show that the electrical performance of polycrystalline films of metal-halide perovskites (MHPs) approaches that of single crystals at room temperature. Combining temperature-dependent terahertz conductivity measurements and ab initio calculations we uncover a complete picture of the origins of charge-carrier scattering in single crystals and polycrystalline films of CH₃NH₃PbI₃. We show that Fröhlich scattering of charge carriers with multiple phonon modes is the dominant mechanism limiting mobility, with grain-boundary scattering further reducing mobility in polycrystalline films. We reconcile the large discrepancy in charge-carrier diffusion lengths between single crystals and films by considering photon reabsorption. Thus, polycrystalline films of MHPs offer great promise for devices beyond solar cells, including light-emitting diodes and modulators.