The alloying of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an established route to produce robust semiconductors with continuously tunable optoelectronic properties. However, typically reported methods for fabricating alloyed 2D TMD nanosheets are not suitable for the inexpensive, scalable production of large-area (m2) devices. Herein we describe a general method to afford large quantities of compositionally-tunable 2D TMD nanosheets using commercially available powders and liquid-phase exfoliation. Beginning with Mo(1-x)WxS(2) nanosheets, we demonstrate tunable optoelectronic properties as a function of composition. We extend this method to produce Mo0.5W0.5Se2 MoSSe, WSSe, and quaternary Mo0.5W0.5SSe nanosheets. High-resolution scanning transmission electron microscopy (STEM) imaging confirms the atomic arrangement of the nanosheets, while an array of spectroscopic techniques is used to characterize the chemical and optoelectronic properties. This transversal method represents an important step towards upscaling tailored TMD nanosheets with a broad range of tunable optoelectronic properties for large-area devices.

Layered halide perovskites (LHPs) are emerging semiconductor materials due to their superior environmental stability compared to traditional halide perovskites. While LHPs have tunable optoelectronic properties, quantum and dielectric confinement effects due to organic spacer layers limit their application. Recent attempts to mitigate the high exciton binding energy (Eb) of LHPs by organic cation engineering have been demonstrated, however systematic studies to decouple the influence of interlayer spacing and molecular dipole are very limited. Here, we designed a new class of organic spacer employing a malononitrile (MN) functionality giving a calculated dipole moment of 7.9 D. Malononitrile phenethyl ammonium (MNPEA) was successfully incorporated into lead iodide-based LHPs thin films and as single crystals. Comparing the MNPEA-based LHP to phenethyl ammonium (PEA) and biphenethyl ammonium (BPEA), selected as reference cations to elucidate the influence of increased dipole moment while excluding the contribution of increased interlayer distance, clarified the effect of the large organic dipole. Binding energies, Eb, estimated by temperature-dependent photoluminescence spectroscopy for MNPEA2PbI4, PEA2PbI4 and BPEA2PbI4 were 122, 354 and 183 meV, respectively. Moreover, the similar interlayer spacing of BPEA2PbI4 and MNPEA2PbI4 (21.04 Å and 21.36 Å, respectively) confirms the importance of dipole on tuning the optoelectronic properties. Photovoltaic devices with n = 1 LHPs demonstrated a higher fill factor and open circuit voltage with MNPEA2PbI4 compared to the reference layered perovskites likely due to the favored charge dissociation and transport afforded by the malononitrile-based cation.

Incorporating organic semiconductor building blocks as spacer cations into layered hybrid perovskites provides an opportunity to develop new materials with novel optoelectronic properties, including nanoheterojunctions that afford spatial separation of electron and hole transport. However, identifying organics with suitable structure and electronic energy levels to selectively absorb visible light has been a challenge in the field. In this work, we introduce a new lead-halide-based Ruddlesden-Popper perovskite structure based on a visible-light-absorbing naphthalene-iminoimide cation (NDI-DAE). Thin films of (NDI-DAE)(2)PbI4 show a quenched photoluminescence and transient absorption dynamics consistent with the formation of a charge transfer state or free charge carriers when either the inorganic or organic layer is photoexcited, suggesting the formation of a type II nanoheterostructure. Time-resolved microwave conductivity analysis supports free charge generation with sum mobilities up to 4 x 10(-4) cm(2) V-1 s(-1). Mixed halide (NDI-DAE)(2)Pb(I-x Br1-x )(4 )films show modified inorganic layer band gaps and a photoluminescent reversed type I nanoheterostructure with high bromide content (e.g., for x = 0). At x = 0.5, transient absorption and microwave conductivity measurements provide strong evidence that selective visible-light absorbance by the NDI-DAE cation generates separated free carriers via hole transfer to the inorganic layer (leaving photogenerated electrons in the organic layer), which represents an important step toward enhancing light harvesting and affording the spatial separation of charge carrier transport in stable layered perovskite-based devices.

An electron-accepting spacer di-cation based on naphthalene diimide is incorporated into layered and quasi-layered perovskite structure, and the effect of the resulting type II heterostructure on the optoelectronic structure is investigated.

Photoelectrochemical (PEC) CO2 reduction has received considerable attention given the inherent sustainability and simplicity of directly converting solar energy into carbon-based chemical fuels. However, complex photocathode architectures with protecting layers and cocatalysts are typically needed for selective and stable operation. We report herein that bare CuIn0.3Ga0.7S2 photocathodes can drive the PEC CO2 reduction with a benchmarking 1 Sun photocurrent density of over 2 mA/cm2 (at -2 V vs Fc+/Fc) and a product selectivity of up to 87% for CO (CO/all products) production while also displaying long-term stability for syngas production (over 44 h). Importantly, spectroelectrochemical analysis using PEC impedance spectroscopy (PEIS) and intensity-modulated photocurrent spectroscopy (IMPS) complements PEC data to reveal that tailoring the proton donor ability of the electrolyte is crucial for enhancing the performance, selectivity, and durability of the photocathode. When a moderate amount of protons is present, the density of photogenerated charges accumulated at the interface drops significantly, suggesting a faster charge transfer process. However, with a high concentration of proton donors, the H2 evolution reaction is preferred.

Gas diffusion electrodes are essential components of common fuel and electrolysis cells but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance and thus limit the development of gas‐phase based photoelectrochemical devices. Herein, the simple and scalable preparation of F‐doped SnO2 (FTO) coated SiO2 interconnected fiber felt substrates is reported. Using 2–5 µm diameter fibers at a loading of 4 mg cm−2, the resulting substrates have porosity of 90%, roughness factor of 15.8, and Young's Modulus of 0.2 GPa. A 100 nm conformal coating of FTO via atmospheric chemical vapor deposition gives sheet resistivity of 20 ± 3 Ω sq−1 and loss of incident light of 41% at illumination wavelength of 550 nm. The coating of various semiconductors on the substrates is established including Fe2O3 (chemical bath deposition), CuSCN and Cu2O (electrodeposition), and conjugated polymers (dip coating), and liquid‐phase photoelectrochemical performance commensurate with flat FTO substrates is confirmed. Finally, gas phase H2 production is demonstrated with a polymer semiconductor photocathode membrane assembly at 1‐Sun photocurrent density on the order of 1 mA cm−2 and Faradaic efficiency of 40%.

Cu2O is a model p-type semiconductor for photocathodesin photoelectrochemical (PEC) water splitting cells. However, majorchallenges remain in controlling its deposition into thin andhomogeneous semitransparentfilms. Herein, we report a new route toconstruct thin homogeneous Cu2O layers on transparentfluorine dopedtin oxide (FTO) substrates via thein situelectroconversion of CuSCN toCu2O. We highlight the morphology control of the resulting convertedCu2O thinfilms while demonstrating that they maintain promisingperformance for solar-driven hydrogen production with a maximumincident photon to current efficiency (IPCE) reaching 60% (at 0 V vsRHE and 450 nm) for a 180 nm thickfilm and integrated solarphotocurrents up to 4 mA cm-2. In addition, altering the depositionconditions (e.g., applied potential, electrolyte compositions, and pH)gives important insight into the mechanism and operation of theelectroconversion process.

Layered hybrid organic-inorganic perovskite (LHOIP) materialsconstructed with low-band-gap chromophore-based organic spacer cations are anemerging class of materials that promise unique tunability of their optoelectronicproperties. However, the large size of such chromophore-based spacer cationschallenges their incorporation into a layered perovskite structure and requires furtherinsight into the layered perovskite phase formation mechanism. Herein, we report thepreparation and incorporation of asymmetric naphthalenediimide (NDI) spacerchromophore cations with different amine-bearing alkyl linker chains into thinfilmsof LHOIPs. Usingin situUV-vis spectroscopic kinetic studies of the quantum wellformation, we show that shorter linker chain lengths require higher annealingtemperatures to form the LHOIP structure. Avrami analysis of the layered perovskiteformation shows a larger Avrami coefficient (n= 3.64) for short linker chain-bearing cations compared to that for longer alkyl chain-bearing cations (n= 2.43), suggesting an evolution from three-dimensional to quasi-two-dimensional crystal growth with increasinglinker chain length. Additionally, transient absorption spectroscopy and broad-bandfluorescent upconversion spectroscopy indicatefast photoinduced charge transfer from the inorganic layer to the electron-accepting NDI-spacer cation.

The tandem synthesis of benzimidazole and other azoles can be achived by the N-formylation of ortho-substituted anilines followed by a cyclization reaction. However, CO2-based N-formylations with hydrosilane reducing agents are base catalyzed whereas the cyclization reaction is acid catalyzed. The mismatch in catalytic conditions means that only one of the steps can be catalyzed in a single pot reaction. While the N-formylation reaction is frequently the target of catalyst development, the cyclization reaction requires comparably much harsher reaction conditions. Identification of these difficulties lead us to the development of a one-pot, two-step synthesis of benzimidazole under mild reaction conditions employing acid catalysts.