Reversible and irreversible trapping at room temperature in poly(thiophene) thin-film transistors

We measured the bias stress characteristics of poly(thiophene) semi-crystalline thin-film transistors (TFTs) as a function stress times, gate voltages and duty-cycles. At room temperature, the bias stress has two components: a fast reversible component and a slow irreversible component. We hypothesize that the irreversible component is due to charge trapping in the disordered areas of the semiconductor film. At low duty-cycle (<2%), the fast bias stress component is reversed during the off-part of the cycle therefore the observed VT shift in only caused by irreversible trapping. Irreversible trapping follows power-law kinetics with a time exponent approximately equal to 0.37. We use these findings to estimate the lifetime of TFTs used as switches in display backplanes

Intrinsic hole mobility and trapping in a regio-regular poly(thiophene)

The transport properties of high-performance thin-film transistors (TFT) made with a regio-regular poly(thiophene) semiconductor (PQT-12) are reported. The room-temperature field-effect mobility of the devices varied between 0.004 cm2/V s and 0.1 cm2/V s and was controlled through thermal processing of the material, which modified the structural order. The transport properties of TFTs were studied as a function of temperature. The field-effect mobility is thermally activated in all films at T<200 K and the activation energy depends on the charge density in the channel. The experimental data is compared to theoretical models for transport, and we argue that a model based on the existence of a mobility edge and an exponential distribution of traps provides the best interpretation of the data. The differences in room-temperature mobility are attributed to different widths of the shallow localized state distribution at the edge of the valence band due to structural disorder in the film. The free carrier mobility of the mobile states in the ordered regions of the film is the same in all structural modifications and is estimated to be between 1 and 4 cm2/V s.Comment: 20 pages, 8 figure

Recovery from water stress in laurel plants: influence of short term potassium fertilization

Plant xylem hydraulic conductance varies with changes in sap solute concentrations, particularly potassium, a phenomenon known as 'ionic effect'. In well-watered Laurus nobilis plants, short term potassium fertilization increased xylem sap potassium concentration, resulting in an increase in plant hydraulic conductance (Kplant), leaf-specific conductivity of the shoot (kshoot) and transpiration rate (Eplant). The ionic effect is enhanced in embolized stems, where it can compensate the cavitation-induced loss of hydraulic conductance. The aim of this work was to test if water-stressed potassium-starved laurel plants could recover earlier from stress when irrigated with a potassium solution instead of water. Two-year-old potted laurel seedlings, grown under potassium-starved conditions, were subjected to water stress by suspending irrigation until leaf conductance to water vapor (gL) dropped to less than 50% of its initial value and leaf water potential (YL) reached turgor loss point (YTLP). Plants were then irrigated either with water or 25 mM KCl and measurements were taken at 3, 6 or 24 hours after irrigation. No significant differences were found between the two groups of plants in terms of YL, gL, Eplant, Kplant or kshoot. Analysis of xylem sap potassium concentration showed there were no significant differences between treatments, and potassium levels were similar to those of potassium-starved well-watered plants. In conclusion, potassium uptake or release to xylem appeared to be impaired at least up to 24 hours after relief from water stress, so fertilization after the onset of stress did not result in any short term advantage for recovery from drought stress

Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) leverage ion injection from an electrolyte into an organic semiconductor film to yield compelling advances in biological interfacing, printed logic circuitry and neuromorphic devices. Their defining characteristic is the coupling between electronic and ionic charges within the volume of an organic film. In this review we discuss the mechanism of operation and the materials that are being used, overview the various form factors, fabrication technologies and proposed applications, and take a critical look at the future of OECT research and development

Tuning the bandgap of Cs2AgBiBr6 through dilute tin alloying.

The promise of lead halide hybrid perovskites for optoelectronic applications makes finding less-toxic alternatives a priority. The double perovskite Cs2AgBiBr6 (1) represents one such alternative, offering long carrier lifetimes and greater stability under ambient conditions. However, the large and indirect 1.95 eV bandgap hinders its potential as a solar absorber. Here we report that alloying crystals of 1 with up to 1 atom% Sn results in a bandgap reduction of up to ca. 0.5 eV while maintaining low toxicity. Crystals can be alloyed with up to 1 atom% Sn and the predominant substitution pathway appears to be a ∼2 : 1 substitution of Sn2+ and Sn4+ for Ag+ and Bi3+, respectively, with Ag+ vacancies providing charge compensation. Spincoated films of 1 accommodate a higher Sn loading, up to 4 atom% Sn, where we see mostly Sn2+ substitution for both Ag+ and Bi3+. Density functional theory (DFT) calculations ascribe the bandgap redshift to the introduction of Sn impurity bands below the conduction band minimum of the host lattice. Using optical absorption spectroscopy, photothermal deflection spectroscopy, X-ray absorption spectroscopy, 119Sn NMR, redox titration, single-crystal and powder X-ray diffraction, multiple elemental analysis and imaging techniques, and DFT calculations, we provide a detailed analysis of the Sn content and oxidation state, dominant substitution sites, and charge-compensating defects in Sn-alloyed Cs2AgBiBr6 (1:Sn) crystals and films. An understanding of heterovalent alloying in halide double perovskites opens the door to a wider breadth of potential alloying agents for manipulating their band structures in a predictable manner

Organic film thickness influence on the bias stress instability in Sexithiophene Field Effect Transistors

In this paper, the dynamics of bias stress phenomenon in Sexithiophene (T6) Field Effect Transistors (FETs) has been investigated. T6 FETs have been fabricated by vacuum depositing films with thickness from 10 nm to 130 nm on Si/SiO2 substrates. After the T6 film structural analysis by X-Ray diffraction and the FET electrical investigation focused on carrier mobility evaluation, bias stress instability parameters have been estimated and discussed in the context of existing models. By increasing the film thickness, a clear correlation between the stress parameters and the structural properties of the organic layer has been highlighted. Conversely, the mobility values result almost thickness independent

On the Potential of Optical Nanoantennas for Visibly Transparent Solar Cells

This study aims to determine the maximum possible energy conversion efficiency of visibly transparent solar cells using the detailed balance limit (also known as the Shockley–Queisser limit) and compare it to the efficiency of traditional single-junction solar cells. To achieve this, a new optical nanoantenna has been designed to absorb incoming light selectively, enhancing the average visible transmission while maintaining high absorption in the infrared and UV regions. The color appearance of the antennas has also been evaluated through colorimetrical characterization. Our findings indicate that it is possible to achieve high average visible transparency and energy conversion efficiency of over 80 and 18%, respectively, by carefully selecting semiconductor materials. Such solar cells are versatile enough to be integrated seamlessly into smart windows, agrivoltaic concepts in open and protected cultivation, mobile devices, and appliances without compromising their appearance or functionality. The dimensions and optics of the proposed antennas and visibly transparent solar cells have been thoroughly discussed