Prediction of the Active Layer Nanomorphology in Polymer Solar Cells Using Molecular Dynamics Simulation

Active layer nanomorphology is a major factor that determines the efficiency of bulk heterojunction polymer solar cells (PSCs). Synthesizing diblock copolymers in which acceptor and donor materials are the constituent blocks is the most recent method to control the structure of the active layer. In the current work, a computational method is proposed to predict the nanomorphology of the active layer consisting of a diblock copolymer. Diblock copolymers have a tendency to self-organize and form well-defined nanostructures. The shape of the structure depends on the Flory–Huggins interaction parameter (i.e., χ), the total degree of polymerization (<i>N</i>) and volume fractions of the constituent blocks (φ_i). In this work, molecular dynamics (MD) simulations were used to calculate χ parameters for two different block copolymers used in PSCs: P3HT-<i>b</i>-poly­(S₈A₂)-C₆₀ and P3HT-<i>b</i>-poly­(n-butyl acrylate-<i>stat</i>-acrylate perylene) also known as P3HT-<i>b</i>-PPerAcr. Such calculations indicated strong segregation of blocks into cylindrical structure for P3HT-<i>b</i>-poly­(S₈A₂)-C₆₀ and intermediate segregation into cylindrical structure for P3HT-<i>b</i>-PPerAcr. Experimental results of P3HT-<i>b</i>-poly­(S₈A₂)-C₆₀ and P3HT-<i>b</i>-PTP4AP, a diblock copolymer having very similar structure to P3HT-<i>b</i>-PPerAcr, validate our predictions

Multinuclear Magnetic Resonance Tracking of Hydro, Thermal, and Hydrothermal Decomposition of CH₃NH₃PbI₃

An NMR investigation of methylammonium lead iodide, the leading member of the hybrid organic–inorganic perovskite class of materials, and of its putative decomposition products as a result of exposure to heat and humidity, has been undertaken. We show that the ²⁰⁷Pb NMR spectra of the compound of interest and of the proposed lead-containing decomposition products, CH₃NH₃PbI₃·H₂O, (CH₃NH₃)₄PbI₆·2H₂O, and PbI₂, have distinctive chemical shifts spanning over 1400 ppm, making ²⁰⁷Pb NMR an ideal tool for investigating this material; further information may be gained from ¹³C and ¹H NMR spectra. As reported in many investigations of CH₃NH₃PbI₃ on films, the bulk material hydrates in the presence of high relative humidity (approximately 80%), yielding the monohydrated perovskite CH₃NH₃PbI₃·H₂O. This reaction is reversible by heating the sample to 341 K. We show that neither (CH₃NH₃)₄PbI₆·2H₂O nor PbI₂ is observed as a decomposition product and that, in contrast to many studies on CH₃NH₃PbI₃ films, the bulk material does not decompose or degrade beyond CH₃NH₃PbI₃·H₂O upon prolonged exposure to humidity at ambient temperature. However, exposing CH₃NH₃PbI₃ concurrently to heat and humidity, or directly exposing it to liquid water, leads to the irreversible formation of PbI₂. In spite of its absence among the decomposition products, the response of (CH₃NH₃)₄PbI₆·2H₂O to heat was also investigated. It is stable at temperatures below 336 K but then rapidly dehydrates, first to CH₃NH₃PbI₃·H₂O and then to CH₃NH₃PbI₃. The higher stability of the bulk material as reported here is a promising advance, since stability is a major concern in the development of commercial applications for this material

Schottky Barrier Thin Film Transistors Using Solution-Processed <i>n</i>‑ZnO

Solution-processed ZnO thin films are attractive as active materials in thin film transistors (TFTs) for low-cost electronic device applications. However, the lack of true enhancement mode operation, low mobility, and unreliability in transistor characteristics due to the high density of traps and other defects present challenges in using such TFTs in circuits. We demonstrate in this report that the electrical characteristics of such TFTs can be improved by source injection barriers. Asymmetrical Schottky source metal–oxide–semiconductor field-effect transistors (MOSFETs) have been fabricated by utilizing heavily doped solution-processed ZnO as the active layer. <i>n</i>^<i>+</i>-ZnO was obtained by using triethylamine as the stabilizer in the solution process instead of the more commonly used monoethanolamine. Au was chosen for source metallization to create a Schottky contact to the ZnO and an Al ohmic contact was chosen as the drain. Voltage applied to the gate induced field emission through the Schottky barrier and allowed modulation of the drain current by varying the width of the barrier. By operating the asymmetrical MOSFET when the Schottky contact is reverse biased, effective control over the transistor characteristics was obtained

Mechanochemical Synthesis of Methylammonium Lead Mixed–Halide Perovskites: Unraveling the Solid-Solution Behavior Using Solid-State NMR

Mixed-halide lead perovskite (MHP) materials are rapidly advancing as next-generation high-efficiency perovskite solar cells due to enhanced stability and bandgap tunability. In this work, we demonstrate the ability to readily and stoichiometrically tune the halide composition in methylammonium-based MHPs using a mechanochemical synthesis approach. Using this solvent-free protocol we are able to prepare domain-free MHP solid solutions with randomly distributed halide ions about the Pb center. Up to seven distinct [PbCl_<i>x</i>Br_6–x]^4– environments are identified, based on the ²⁰⁷Pb NMR chemical shifts, which are also sensitive to the changes in the unit cell dimensions resulting from the substitution of Br by Cl, obeying Vegard’s law. We demonstrate a straightforward and rapid synthetic approach to forming highly tunable stoichiometric MHP solid solutions while avoiding the traditional solution synthesis method by redirecting the thermodynamically driven compositions. Moreover, we illustrate the importance of complementary characterization methods, obtaining atomic-scale structural information from multinuclear, multifield, and multidimensional solid-state magnetic resonance spectroscopy, as well as from quantum chemical calculations and long-range structural details using powder X-ray diffraction. The solvent-free mechanochemical synthesis approach is also compared to traditional solvent synthesis, revealing identical solid-solution behavior; however, the mechanochemical approach offers superior control over the stoichiometry of the final mixed-halide composition, which is essential for device engineering

Nanosecond Laser Confined Bismuth Moiety with Tunable Structures on Graphene for Carbon Dioxide Reduction

Substrate-supported catalysts with atomically dispersed metal centers are promising for driving the carbon dioxide reduction reaction (CO2RR) to produce value-added chemicals; however, regulating the size of exposed catalysts and optimizing their coordination chemistry remain challenging. In this study, we have devised a simple and versatile high-energy pulsed laser method for the enrichment of a Bi “single atom” (SA) with a controlled first coordination sphere on a time scale of nanoseconds. We identify the mechanistic bifurcation routes over a Bi SA that selectively produce either formate or syngas when bound to C or N atoms, respectively. In particular, C-stabilized Bi (Bi–C) exhibits a maximum formate partial current density of −29.3 mA cm–2 alongside a TOF value of 2.64 s–1 at −1.05 V vs RHE, representing one of the best SA-based candidates for CO2-to-formate conversion. Our results demonstrate that the switchable selectivity arises from the different coupling states and metal-support interactions between the central Bi atom and adjacent atoms, which modify the hybridizations between the Bi center and *OCHO/*COOH intermediates, alter the energy barriers of the rate-determining steps, and ultimately trigger the branched reaction pathways after CO2 adsorption. This work demonstrates a practical and universal ultrafast laser approach to a wide range of metal–substrate materials for tailoring the fine structures and catalytic properties of the supported catalysts and provides atomic-level insights into the mechanisms of the CO2RR on ligand-modified Bi SAs, with potential applications in various fields

Tunable Absorption and Emission in Mixed Halide Bismuth Oxyhalides for Photoelectrochemical Water Splitting

Layered materials such as bismuth oxyhalides (especially BiOBr and BiOI) are the focus of research attention as photocatalysts due to their visible light activity, unique electronic structure, excellent chemical and physical stability, and internal electric field effect. We report the solvothermal synthesis of BiOX solid solutions with continuously tunable optical absorption and photoluminescence spectra. We employed solid-state nuclear magnetic resonance (SSNMR) characterization to probe the local environment around Bi atoms. We determined that the synthesized BiOX solid solutions exhibit good agreement with Vegard’s law through refinement of the lattice parameters using powder X-ray diffraction (PXRD) and complementary atomic-level 209Bi SSNMR spectroscopy. The solid solution strategy makes it possible to modulate the light absorption of BiOX and tune the redox potentials corresponding to the electronic band edges to drive chemical reactions. The BiOX solid solutions demonstrated superior performance in sunlight-driven photoelectrochemical and photocatalytic water splitting. The best performing solid solution generated a photocurrent density of 1.5 mA cm–2 and a H2 evolution rate of 16.32 μmol g–1 h–1 for photoelectrochemical water splitting and photocatalytic hydrogen generation, respectively, and the enhanced performance is attributed to a higher specific surface area, a shorter carrier transit distance, and a higher electron density. The approximate order of magnitude performance improvement compared to pristine BiOBr and BiOI photoanodes was primarily due to optimal light harvesting combined with adequate thermodynamic driving force to drive water oxidation and proton reduction

Composition-Tunable Formamidinium Lead Mixed Halide Perovskites via Solvent-Free Mechanochemical Synthesis: Decoding the Pb Environments Using Solid-State NMR Spectroscopy

Mixed-halide lead perovskites are becoming of paramount interest in the optoelectronic and photovoltaic research fields, offering band gap tunability, improved efficiency, and enhanced stability compared to their single halide counterparts. Formamidinium-based mixed halide perovskites (FA-MHPs) are critical to obtaining optimum solar cell performance. Here, we report a solvent-free mechanochemical synthesis (MCS) method to prepare FA-MHPs, starting with their parent compounds (FAPbX₃; X = Cl, Br, I), achieving compositions not previously accessible through the solvent synthesis (SS) technique. By probing local Pb environments in MCS FA-MHPs using solid-state nuclear magnetic resonance spectroscopy, along with powder X-ray diffraction for long-range crystallinity and reflectance measurements to determine the optical band gap, we show that MCS FA-MHPs form atomic-level solid solutions between Cl/Br and Br/I MHPs. Our results pave the way for advanced methods in atomic-level structural understanding while offering a one-pot synthetic approach to prepare MHPs with superior control of stoichiometry