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Metal–organic species can be designed to self-assemble in large-scale, atomically defined, supramolecular architectures. A particular example is hybrid quantum wells, where inorganic two-dimensional (2D) planes are separated by organic ligands. The ligands effectively form an intralayer confinement for charge carriers resulting in a 2D electronic structure, even in multilayered assemblies. Air-stable layered transition metal organic chalcogenides have recently been found to host tightly bound 2D excitons with strong optical anisotropy in a bulk matrix. Here, we investigate the excited carrier dynamics in the prototypical metal–organic chalcogenide [AgSePh]∞, disentangling three excitonic resonances by low temperature transient absorption spectroscopy. Our analysis suggests a complex relaxation cascade comprising ultrafast screening and renormalization, interexciton relaxation, and self-trapping of excitons within a few picoseconds (ps). The ps-decay provided by the self-trapping mechanism may be leveraged to unlock the material’s potential for ultrafast optoelectronic applications.

Silver benzeneselenolate [AgSePh]∞is a coordination polymer that hosts a hybrid quantum well structure. The recent advancements in the study of its tightly bound excitons (∼300 meV) and photoconductive properties (recently employed in UV photodetection) make it an interesting representative of a material platform that is an environmentally stable alternative to 2D metal halide perovskites in terms of optoelectronic properties. To this aim, several challenges are to be addressed, among which is the lack of control over the metal–organic reaction process in the reported synthesis of the [AgSePh]∞nanocrystal film (NC). This issue contributed to cast doubts over the origin of its intrabandgap electronic states. In this article we study all the steps to obtain phase pure [AgSePh]∞NC films, from thin silver films deposition through its oxidation followed by a chemical vapor–solid reaction with benzeneselenol, by means of UV–vis, XRD, SEM, and AFM. Raman and FTIR spectroscopies are also employed to provide vibrational peaks assignment for the first time on this polymer. Our analysis supports an acid–base reaction scheme based on an acid attacking the metal oxide precursor, generating water as a byproduct of the polymeric synthesis, speeding up the reaction by solvating the PhSeH. The reaction readily goes to completion within 30 min in a supersaturated PhSeH/N2atmosphere at 90 °C. Our analysis suggests the absence of the precursor’s leftovers or oxidized species that could contribute to the intragap states. By tuning the reaction parameters, we gained control of film morphology to obtain substrate-parallel oriented microcrystals showing different excitonic absorption intensities. Finally, centimeter-size high-quality [AgSePh]∞NC films could be obtained, enabling exploitation of their optoelectronic properties, such as UV photodetection, in large-area applications.

Here, we lay the design rules for linking microporous polymer membrane architecture and pore chemistry to membrane stability, conductivity, and transport selectivity in aqueous electrolytes over a broad range of pH. We tie these attributes to prospects for crossover-free electrochemical cell operation. These guiding principles are applied to two emerging cell chemistries for grid batteries: specifically, Zn–TEMPO-4-sulfate and Zn–K4Fe(CN)6cells. Key to our success is the placement of ionizable amidoxime functionalities, which are stable at high pH, within the pores of microporous ladder polymer membranes, yielding a family of charge-neutral and cation exchange membranes at low and high pH, respectively—which we call AquaPIMs. Their notably high conductivity (up to 21.5 mS cm−1in 5.0 M aqueous KOH) and high transport selectivity (up to 104reduction in active-material permeability through the membrane) suggest exciting opportunities for battery development, even beyond those presently demonstrated.

Ternary structure is an important design strategy to obtain high-efficiency non-fullerene organic photovoltaics (OPVs). However, the role of the third component to the standard binary system is still unclear. Here, a wide-bandgap small-molecule acceptor, denoted IDT-T, is synthesized and used together with a wide-bandgap donor polymer, PBDB-T, and a low-bandgap acceptor, ITIC, for fullerene-free ternary solar cells. The ternary cell features an enhanced power conversion efficiency (PCE) up to 12.2%, together with improved photocurrent density, open-circuit voltage (VOC), and fill factor. Studies of the thin films indicate that IDT-T functions as an energy-level mediator, a fluorescence resonance energy-transfer donor, an electron acceptor, and a crystallization modulator in the blend, which contribute synergistically in the ternary blend to deliver a higher VOC, more efficient exciton generation, suppressed bimolecular charge recombination and enhanced charge transport, and an overall high photovoltaic performance.

CdS nanocrystals (NCs) synthesized by colloidal chemistry methods have been intensively studied for various applications. However, little attention has been paid to the interaction between the oxygen molecules present in air and the NC surface, which has a strong influence on the electrical properties of NC films. Here, we discuss the effect of oxygen adsorption at the NC surface on the photoconductivity of CdS NC films that were treated by propyltrichlorosilane, which is known to replace the native ligands at the NC surface with chloride ions. The photocurrent–voltage (PIV) characteristics of NC@Cl films recorded under oxygen atmosphere reveal a significant reduction in the photocurrent, as compared to those recorded under argon or vacuum. We demonstrate that this reduction can be related to adsorbed oxygen ions that effectively passivate the NC surface. This passivation reduces the free electron concentration and thereby reduces the photocurrent. Furthermore, we have investigated the light intensity dependence of the photocurrent dynamics of our devices in argon and in oxygen. These measurements confirm that the adsorption of oxygen is a photo-assisted process. Eventually, the potential of using our devices as oxygen sensors is assessed. A remarkable sensitivity of 35 is obtained at room temperature for 10% (concentration) oxygen flow, which is at least one order of magnitude higher than the results reported in the literature. Our work clarifies the mechanism of the photoconductivity reduction in CdS NC films upon oxygen adsorption and opens up opportunities of exploring such devices for gas sensing applications.

We demonstrate a process for batch production of large-area (100−3000 μm2) patterned free-standing graphene membranes on Cu scaffolds using chemical vapor deposition (CVD)-grown graphene. This technique avoids the use of silicon and transfers of graphene. As one application of this technique, we fabricate transmission electron microscopy (TEM) sample supports. TEM characterization of the graphene membranes reveals relatively clean, highly TEM-transparent, single-layer graphene regions (∼50% by area) and, despite the polycrystalline nature of CVD graphene, membrane yields as high as 75−100%. This high yield verifies that the intrinsic strength and integrity of CVD-grown graphene films is sufficient for sub-100 μm width membrane applications. Elemental analysis (electron energy loss spectroscopy (EELS) and X-ray energy-dispersive spectroscopy (EDS)) of the graphene membranes reveals some nanoscaled contamination left over from the etching process, and we suggest several ways to reduce this contamination and improve the quality of the graphene for electronic device applications. This large-scale production of suspended graphene membranes facilitates access to the two-dimensional physics of graphene that are suppressed by substrate interactions and enables the widespread use of graphene-based sample supports for electron and optical microscopy.