Isovalent alloying in printable metal dichalcogenide nanomaterials enables precise, application-targeted property tuning. However, a scalable platform offering broad optical and electrical tunability has so far remained elusive. Herein, we establish a powder-based, solution-processed route to access the full domain of SnSxSe(2-x) alloy nanosheets, providing control over a wide range of properties through chalcogenide composition. The n-type nanosheet alloy series shows a wide spread in optical and in-plane electrical properties, ranging from 1.67 eV and low bandgap metallic-like behavior for 2D SnSe2, to 2.46 eV and wide bandgap semiconducting behavior with high-resistivity for 2D SnS2. The out-of-plane conductivity is also tunable, showing nonmonotonic behavior with an optimal chalcogenide ratio of x = 1.2 – 1.6. Using photoelectrochemistry as an example, we highlight how the interplay of these tunable properties enables optimized performance for targeted applications. The exceptional range of tailorable properties reported here provides a roadmap for tuning these alloys, thereby opening avenues for their potential application in a multitude of fields. ... Read more

Carrier multiplication (CM), where a single high-energy photon generates multiple electron–hole pairs, offers a promising route to enhance the efficiency of solar cells and photodetectors.Transition metal dichalcogenides, such as 2H-MoTe2 and 2H-WSe2, exhibit efficient CM. Given the similar electronic band structure of 2H-MoSe2, it is expected to show comparable CM efficiency. In this study, we establish the occurrence and efficiency of CM in a solution-processed thin film of bulk-like 2H-MoSe2. We characterize the dynamics of excitons and free charge carriers by using ultrafast transient optical absorption and terahertz spectroscopy. At higher photon energy the efficiency is comparable to literature results for 2H-MoTe2 grown by chemical vapor deposition (CVD) or in bulk crystalline form. At higher photon energies the experimental CM efficiency is reproduced by theoretical modeling. We also observe CM for photon energies below the energetic threshold of twice the band gap, which is most probably due to subgap defect states. Transient optical absorption spectra of 2H-MoSe2 exhibit features of trions from which we infer that photoexcitation leads to free charge carriers. We find no signatures of excitons at the indirect band gap. From analysis of the frequency dependence of the terahertz conductivity we infer that scattering of charge carriers in our sample is less than for CVD grown or bulk crystalline 2H-MoTe2. Our findings make solution-processed 2H-MoSe2 an interesting material for exploitation of CM in photovoltaic devices. ... Read more

High aspect-ratio 2D materials are promising for solution-processed electronics, yet the factors controlling exfoliation remain unclear and relatively few solution-processed networks have been electrically characterized. Here we combine theory and experiment to show that electrochemical exfoliation of layered crystals with sufficient stiffness-anisotropy (in-plane/out-of-plane Young’s modulus ratio >1.7) yields high aspect-ratio nanosheets with intrinsic mobilities μ_NS = 20–75 cm²V⁻¹s⁻¹ across transition metal dichalcogenides and related alloys. Impedance spectroscopy indicates that solution-deposited networks can achieve junction-to-nanosheet resistance ratios (R_J/R_NS) as low as ~3, supporting theoretical predictions that μ_NS/μ_Net = R_J/R_NS + 1 and suggesting that further reductions in R_J will increase μ_Net toward the nanosheet limit (μ_NS). These networks display n-type, p-type, and ambipolar behaviour, with on/off ratios up to 10⁵ and mobilities μ_Net = 13 cm²V⁻¹s⁻¹. Here, we show that such high-performing 2D materials enable functional solution-processed circuits, including inverters, buffers, a 4-bit digital-to-analog converter, and a circuit capable of encoding and decoding 7-bit ASCII messages. ... Read more

Networks of nanowires, nanotubes, and nanosheets are important for many applications in printed electronics. However, the network conductivity and mobility are usually limited by the resistance between the particles, often referred to as the junction resistance. Minimising the junction resistance has proven to be challenging, partly because it is difficult to measure. Here, we develop a simple model for electrical conduction in networks of 1D or 2D nanomaterials that allows us to extract junction and nanoparticle resistances from particle-size-dependent DC network resistivity data. We find junction resistances in porous networks to scale with nanoparticle resistivity and vary from 5 Ω for silver nanosheets to 24 GΩ for WS2 nanosheets. Moreover, our model allows junction and nanoparticle resistances to be obtained simultaneously from AC impedance spectra of semiconducting nanosheet networks. Through our model, we use the impedance data to directly link the high mobility of aligned networks of electrochemically exfoliated MoS2 nanosheets (≈ 7 cm2 V−1 s−1) to low junction resistances of ∼2.3 MΩ. Temperature-dependent impedance measurements also allow us to comprehensively investigate transport mechanisms within the network and quantitatively differentiate intra-nanosheet phonon-limited bandlike transport from inter-nanosheet hopping. ... Read more

Photo-conductive antennas (PCAs) are the workhorse of time-domain THz sensing and imaging. In this work, we employ a rigorous Norton equivalent circuit model to identify and estimate the substrate-related parasitic effects, that might limit the THz emission, to better design future PCAs. ... Read more