Transparent, conductive solution processed spincast 2D Ti2CTx (MXene) films

Herein, we spincast aqueous colloidal Ti2CTx (MXene) solutions into conductive, transparent films with figures of merit (FOM), that are as good as Ti3C2Tx or un-doped chemically vapor-deposited graphene. When normalized by the number of transition metal atoms, the FOM is the highest ever reported for a MXene film. At about 2.7 × 105 cm–1 the absorbance coefficient of Ti2CTx is quite comparable to that of Ti3C2Tx. Quantitative relationships between film properties—conductance and transparency—and colloidal solution concentration and spin speeds are developed providing a road map for future work

Transparent, conductive solution processed spincast 2D Ti₂CT<i>_x</i> (MXene) films

<p>Herein, we spincast aqueous colloidal Ti₂CT<i>_x</i> (MXene) solutions into conductive, transparent films with figures of merit (FOM), that are as good as Ti₃C₂T<i>_x</i> or un-doped chemically vapor-deposited graphene. When normalized by the number of transition metal atoms, the FOM is the highest ever reported for a MXene film. At about 2.7 × 10⁵ cm^–1 the absorbance coefficient of Ti₂CT_x is quite comparable to that of Ti₃C₂T_x. Quantitative relationships between film properties—conductance and transparency—and colloidal solution concentration and spin speeds are developed providing a road map for future work.</p> <p><b>IMPACT STATEMENT</b></p> <p>In a first, we spincast aqueous colloidal Ti₂CT<i>_x</i> (MXene) solutions into conductive, transparent films with figures of merit—5—that are as good as Ti₃C₂T<i>_x</i> or un-doped CVD graphene.</p

Slow Electron–Hole Recombination in Lead Iodide Perovskites Does Not Require a Molecular Dipole

Hybrid organic/inorganic lead iodide perovskites of the formula APbI₃, where A is a molecular cation such as methylammonium, exhibit remarkably slow photoinduced charge carrier recombination rates, for reasons that remain uncertain. Prevalent hypotheses credit this behavior to the unique dipolar nature of the molecular cation. Herein, transient terahertz spectroscopy is applied to solution-processed, all-inorganic, perovskite-phase cesium lead iodide (CsPbI₃) thin films, which lack such a dipole. The recombination kinetics are studied as a function of the initial photoinduced carrier concentration and the wavelength of excitation. A kinetic model combining diffusion and recombination is fit to the data, from which the rate constants are determined, revealing a bimolecular recombination rate of 10^–10 cm³ s^–1, comparable to high-quality, single-crystal, direct-gap semiconductors. This rate, as well as a charge carrier mobility > 30 cm² V^–1 s^–1 measured herein for CsPbI₃, are similar to values reported for the hybrid perovskites, strongly suggesting that the organic cation does not confer a fundamental advantage

Thiocyanate-Capped PbS Nanocubes: Ambipolar Transport Enables Quantum Dot Based Circuits on a Flexible Substrate

We report the use of thiocyanate as a ligand for lead sulfide (PbS) nanocubes for high-performance, thin-film electronics. PbS nanocubes, self-assembled into thin films and capped with the thiocyanate, exhibit ambipolar characteristics in field-effect transistors. The nearly balanced, high mobilities for electrons and holes enable the fabrication of CMOS-like inverters with promising gains of ∼22 from a single semiconductor material. The mild chemical treatment and low-temperature processing conditions are compatible with plastic substrates, allowing the realization of flexible, nonsintered quantum dot circuits

Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature optical properties of CdSe quantum dot solids after exchanging native aliphatic ligands for thiocyanate and subsequent thermal annealing. In contrast to trends established at room temperature, our data show that at low temperature the band-edge absorptive bleach is dominated by 1S_3/2h hole occupation in the quantum dot interior. We find that our ligand treatments, which bring enhanced interparticle coupling, lead to faster surface state electron trapping, a greater proportion of surface-related photoluminescence, and decreased band-edge photoluminescence lifetimes