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High contact resistance has been a bottleneck in developing high-performance transition-metal dichalcogenide (TMD) based p-type transistors. We report degenerately doped few-layer WSe2transistors with contact resistance as low as 0.23 ± 0.07 kΩ·μm per contact by using platinum(IV) chloride (PtCl4) as the p-type dopant, which is composed of ions compatible with the complementary metal-oxide-semiconductor (CMOS) fabrication process. Top-gated devices with a gate length of 200 nm showed good switching behaviors, implying that the dopant diffusion into the gate stack is not significant. The devices showed nearly identical performance after being kept in air for 86 days without any encapsulation while retaining the degenerately doped states at 78 K with pressure lower than 10–5Torr, highlighting the stability of the dopants. The presented method sets forth the availability of highly stable methods for pattern doping the transistors with a thinned Schottky barrier width for low contact resistance devices.

Since coming to power in 1997, education has been at the heart of New Labour's domestic agenda, with Tony Blair declaring that 'education, education, education' were his top three domestic […]

Antimony sulfide (Sb2S3) is a promising light-absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb2S3was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240–300 °C) with elemental sulfur. Using a TiO2buffer layer and a platinum co-catalyst, photocurrent densities up to ∼9 mA cm–2were achieved at −0.4 V vs RHE in 1 M H2SO4under one sun illumination. Using X-ray photoelectron spectroscopy band alignment studies and potential-dependent incident photon-to-current efficiency measurements, a conduction band offset of 0.7 eV was obtained for the Sb2S3/TiO2junction as well as an unfavorable band bending at the heterointerface, which explains the low photovoltage that was observed (∼0.1 V). Upon inserting an In2S3buffer layer, which offers a better band alignment, a 0.15 V increase in photovoltage was obtained. The excellent photoelectrochemical water splitting performance and the identification of the origin of the low photovoltage of the Sb2S3photocathodes in this work pave the way for the further development of this promising earth-abundant light-absorbing semiconductor for solar fuel generation.

Intercalation is the process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on the intercalation of metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains challenging. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface. We investigate the intercalation of phosphorus pentoxide (P2O5) molecules directly from the vapor phase and confirm the formation of confined P2O5at the graphene-substrate heterointerface using various techniques. Density functional theory (DFT) corroborates the experimental results and reveals the intercalation mechanism, whereby P2O5dissociates into small fragments catalyzed by defects in the graphene that then permeates through lattice defects and reacts at the heterointerface to form P2O5. This process can also be used to form new confined metal phosphates (e.g., 2D InPO4). While the focus of this study is on P2O5intercalation, the possibility of intercalation from predissociated molecules catalyzed by defects in graphene may exist for other types of molecules as well. This in-depth study advances our understanding of intercalation routes of large molecules via the basal plane of graphene as well as heterointerface chemical reactions leading to the formation of distinctive confined complex oxide compounds.

Iron pyrite has received significant attention due to its high optical absorption. However, the loss of open circuit voltage (Voc) prevents its further application in photovoltaics. Herein, we have studied the photophysics of pyrite by ultrafast laser spectroscopy to understand fundamental limitation of low Vocby quantifying photocarrier losses in high quality, stoichiometric, and phase pure {100} faceted pyrite nanocubes. We found that fast carrier localization of photoexcited carriers to indirect band edge and shallow trap states is responsible for major carrier loss. Slow relaxation component reflects high density of defects within the band gap which is consistent with the observed Mott-variable range hopping (VRH) conduction from transport measurements. Magnetic measurements strikingly show the magnetic ordering associated with phase inhomogeneity, such as FeS2−δ(0 ≤ δ ≤ 1). This implies that improvement of iron pyrite solar cell performance lies in mitigating the intrinsic defects (such as sulfur vacancies) by blocking the fast carrier localization process. Photocarrier generation and relaxation model is presented by comprehensive analysis. Our results provide insight into possible defects that induce midgap states and facilitate rapid carrier relaxation before collection.

Replacement of lead in the hybrid organic–inorganic perovskite solar cells invokes the need for non-toxic materials such as Sn. Although solution processed CsSnI3has been demonstrated as a lead-free halide perovskite which can function as a light absorber with high photocurrent densities, the power conversion efficiencies were bottlenecked by low open circuit voltages. In this work, the open circuit voltages are modulated by chemical doping of CsSnI3with Br leading to formation of CsSnI3-xBrx(0 ≤ x≤ 3) perovskites. The beneficial effect of Br incorporation for Vocimprovement is evident for CsSnI3system even without the addition of SnF2. There is an evolution of the crystal structure of CsSnI3from orthorhombic to cubic for CsSnBr3accompanied by changes in its optical properties with a blue shift of the absorption and IPCE onset, as the Br–doping is increased. The Vocenhancement is attributed to the decrease in Sn vacancies which is reflected by the lower charge carrier densities of 1015cm–3and a high resistance to charge recombination in case of Br rich CsSnI3-xBrxperovskite. By the addition of SnF2to CsSnI3-xBrxperovskite, the current densities are improved significantly.

Iron pyrite has been the material of interest in the solar community due to its optical properties and abundance. However, the progress is marred due to the lack of control on the surface and intrinsic chemistry of pyrite. In this report, we show iron pyrite as an efficient counter electrode (CE) material alternative to the conventional Pt and poly(3,4-ethylenedioxythiophene (PEDOT) CEs in dye-sensitized solar cells (DSSCs). Pyrite film CEs prepared by spray pyrolysis are utilized in I3–/I–and Co(III)/Co(II) electrolyte-mediated DSSCs. From cyclic voltammetry and impedance spectroscopy studies, the catalytic activity is found to be comparable with that of Pt and PEDOT in I3–/I–and Co(III)/Co(II) electrolyte, respectively. With the I3–/I–electrolyte, photoconversion efficiency is found to be 8.0% for the pyrite CE and 7.5% for Pt, whereas with Co(III)/Co(II) redox DSSCs, efficiency is found to be the same for both pyrite and PEDOT (6.3%). The excellent performance of the pyrite CE in both the systems makes it a distinctive choice among the various CE materials studied.

A novel approach to produce earth-abundant Cu2FeSnS4(CFTS) thin film using spray pyrolysis of nontoxic aqueous precursors followed by sulfurization is reported. The CFTS phase formation was confirmed by both Raman spectroscopy and X-ray diffraction techniques. Hall measurements of these films reveal p-type conductivity with good charge carrier density and mobilities appropriate for solar harvesting devices. To the best of our knowledge, this is the first report on the electrical properties of solution-processed Cu2FeSnS4thin films estimated using Hall measurements. Dye-sensitized solar cells (DSSC) fabricated with CFTS thin film as a photocathode in iodine/iodide electrolyte exhibit good power conversion efficiency, 8.03%, indicating that CFTS would be a promising cheaper alternative to replace Pt as a counter electrode in DSSCs.

Solution processed zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated by varying the Zn/Sn composition. The addition of Sn to the zinc oxide (ZnO) films resulted in improved electrical characteristics, with devices of Zn0.7Sn0.3O composition showing the highest mobility of 7.7 cm2/(V s). An improvement in subthreshold swings was also observed, indicative of a reduction of the interfacial trap densities. Mobility studies at low temperature have been carried out, which indicated that the activation energy was reduced with Sn incorporation. Kelvin probe force microscopy was performed on the films to evaluate work function and correlated to the metal–semiconductor barrier indicating Zn0.7Sn0.3O films had the smallest barrier for charge injection. Organic–inorganic hybrid complementary inverters with a maximum gain of 10 were fabricated by integrating ZTO TFTs with poly-3-hexylthiophene (P3HT) transistors.

We first report the exceptional cycleability of SnO2anodes by atomic layer deposition (ALD) over directly on stainless steel substrates without any capacity fade for 500 cycles. Perfect choice of cycling potential (5–800mV vs.Li) and synthesis condition yielded such performance with reversible capacity of 646mAhg−1at current density of 5μAcm−2. Further, SnO2undergoes the conversion reaction along with alloying reaction enables higher capacity than alloying reaction, however, experiencing severe capacity fade during cycling. Obtained results on SnO2anodes by ALD technique certainly influence the impact on the development of solid-state, thin film and 3D Li-ion batteries.

One dimensional TiO2-B nanorods are synthesized by a conventional hydrothermal approach under highly concentrated alkali hydroxide solutions. Various characterization techniques such as X-ray diffraction, Raman studies, BET surface area measurements, scanning electron microscopy and transmission electron microscopy (TEM) are utilized. Electrochemical Li-insertion properties are evaluated by means of half-cell configuration (Li/TiO2-B) which delivered a discharge capacity of 195 mA h g−1at a current density of 150 mA g−1under ambient temperature conditions. The test cell, Li/TiO2-B, displayed good cycling profiles up to 500 cycles with columbic efficiency over 99.5%. Full-cell, LiMn2O4/TiO2-B, is fabricated and tested both in conventional liquid and PVdF-HFP membranes at a current density of 150 mA g−1and exhibited an excellent cycleability up to 1000 cycles at an operating potential of ∼2.5 V. The results demonstrate the improved electrochemical performance and durability of one dimensional nanostructures i.e.TiO2-B nanorods and electrospun membranes during prolonged cycling. In addition, ex-situTEM analysis revealed the retention of nanorod morphology along with the crystalline structure after 1000 cycles in full-cell assembly, which ensures excellent long-term cycleability of TiO2-B anodes.

Zn-doped SnO2nanocrystals with different doping concentrations were synthesized and the nanocrystal photoanode based DSSC achieved a PCE of 2.07% with a high Voc(0.67 V). TiCl4modification of the photoanode greatly improves the charge injection efficiency and charge collection efficiency and the resulting PCE increased to 4.32% despite a decreased dye adsorption. The Zn-doped SnO2nanocrystals will be of particular interest as photoanode material in DSSCs.