Ferroelectric PVDF nanofiber membrane for high-efficiency PM0.3 air filtration with low air flow resistance.

The significant public health concerns related to particulate matter (PM) air pollutants and the airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have led to considerable interest in high-performance air filtration membranes. Highly ferroelectric polyvinylidene fluoride (PVDF) nanofiber (NF) filter membranes are successfully fabricated via electrospinning for high-performance low-cost air filtration. Spectroscopic and ferro-/piezoelectric analyses of PVDF NF show that a thinner PVDF NF typically forms a ferroelectric ß phase with a confinement effect. A 70-nm PVDF NF membrane exhibits the highest fraction of ß phase (87%) and the largest polarization behavior from piezoresponse force microscopy. An ultrathin 70-nm PVDF NF membrane exhibits a high PM0.3 filtration efficiency of 97.40% with a low pressure drop of 51 Pa at an air flow of 5.3 cm/s owing to the synergetic combination of the slip effect and ferroelectric dipole interaction. Additionally, the 70-nm PVDF NF membrane shows excellent thermal and chemical stabilities with negligible filtration performance degradation (air filtration efficiency of 95.99% and 87.90% and pressure drop of 55 and 65 Pa, respectively) after 24 h of heating at 120 °C and 1 h immersion in isopropanol.

An improvement of performance in n-channel organic field effect transistors with N-phenyl[60]fulleropyrrolidines by molecular doping.

The high performance of soluble [60]fulleropyrrolidine upon its use as the active layer of n-channel organic field-effect transistors (OFETs) is reported. The two materials, N-phenyl derivatives C60-fused-N-phenyl-2-phenylpyrrolidine ([C60]PhNPh) and C60-fused N-phenyl-2-hexylpyrrolidine ([C60]HexNPh), have well-controlled molecular structures with a modification of the pyrrolidine ring, with no increase in the LUMO level, achieving a high mobility and highly ambient stable n-type OFET. The top-gate, bottom-contact device shows a high electron charge-carrier mobility of up to 0.14 and 0.08 cm(2) V(-1) s(-1) for [C60]PhNPh and [C60]HexNPh, respectively, (Ion/Ioff = 10(6)) with the commonly used CYTOP dielectric. Excess carriers introduced by a small amount of chemical doping of polyethyleneimine (PEI) compensate traps by shifting the Fermi level (EF) toward the respective transport energy levels and therefore increase charge-carrier mobility (0.26 and 0.1 cm(2) V(-1) s(-1)) and provide good ambient operational stability compared with pristine devices.

Improved electron transport properties of n-type naphthalenediimide polymers through refined molecular ordering and orientation induced by processing solvents.

To determine the role played by the choice of processing solvents in governing the photophysics, microstructure, and charge carrier transport in naphthalenediimide (NDI)-based polymers, we have prepared two new NDI-bithiophene (T2)- and NDI-thienothiophene (TTh)-containing polymers with hybrid siloxane pentyl chains (SiC5) (P(NDI2SiC5-T2) and P(NDI2SiC5-TTh)). Among the various processing solvents studied here, the films prepared using chloroform exhibited far better electron mobilities (0.16 ± 0.1-0.21 ± 0.05 cm(2) V(-1) s(-1)) than the corresponding samples prepared from different solvents, exceeding one order of magnitude higher, indicating the significant influence of the processing solvent on the charge transport. Upon thin-film analysis using atomic force microscopy and grazing incidence X-ray diffraction, we discovered that molecular ordering and orientation are affected by the choice of the processing solvent, which is responsible for the change in the transport characteristics of this class of polymers.

Controlling charge injection properties in polymer field-effect transistors by incorporation of solution processed molybdenum trioxide.

A simply and facilely synthesized MoO3 solution was developed to fabricate charge injection layers for improving the charge-injection properties in p-type organic field-effect transistors (OFETs). By dissolving MoO3 powder in ammonium (NH3) solvent under an air atmosphere, an intermediate ammonium molybdate ((NH4)2MoO4) precursor is made stable, transparent and spin-coated to form the MoO3 interfacial layers, the thickness and morphology of which can be well-controlled. When the MoO3 layer was applied to OFETs with a cost-effective molybdenum (Mo) electrode, the field-effect mobility (µFET) was significantly improved to 0.17 or 1.85 cm(2) V(-1)s(-1) for polymer semiconductors, regioregular poly(3-hexylthiophene) (P3HT) or 3,6-bis-(5bromo-thiophen-2-yl)-N,N'-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-c]pyrrole (DPPT-TT), respectively. Device analysis indicates that the MoO3-deposited Mo contact exhibits a contact resistance RC of 1.2 MΩ cm comparable to that in a device with the noble Au electrode. Kelvin-probe measurements show that the work function of the Mo electrode did not exhibit a dependence on the thickness of MoO3 film. Instead, ultraviolet photoemission spectroscopy results show that a doping effect is probably induced by casting the MoO3 layer on the P3HT semiconductor, which leads to the improved hole injection.

Hydroxycinnamic acid derivatives for UV-selective and visibly transparent dye-sensitized solar cells.

Naturally abundant dyes are very attractive for the development of dye-sensitized solar cells (DSSCs). Hydroxycinnamic acid derivatives, such as caffeic acid (CA), ferulic acid (FA), and p-coumaric acid (PA), were considered for the selective harvesting of ultraviolet A (UVA) (315-400 nm) photons. Their spectroscopic and electrochemical properties were investigated both theoretically and experimentally. They were further successfully adopted as photosensitizers in UV-selective and visibly transparent DSSCs, which exhibited a power conversion efficiency of 0.22-0.38% under AM (air mass) 1.5G (global) illumination (100 mW/cm2) and 3.40-3.62% under UVA irradiation (365 nm, 115.22 mW/cm2), with a corresponding visible light transmittance (VLT) of 49.07-43.72% and a general color rendering index (Ra) of 93-90.

Transparent Platinum Counter Electrode Prepared by Polyol Reduction for Bifacial, Dye-Sensitized Solar Cells.

Pt catalytic nanoparticles on F-doped SnO2/glass substrates were prepared by polyol reduction below 200 °C. The polyol reduction resulted in better transparency of the counter electrode and high power-conversion efficiency (PCE) of the resultant dye-sensitized solar cells (DSSCs) compared to conventional thermal reduction. The PCEs of the DSSCs with 5 µm-thick TiO2 photoanodes were 6.55% and 5.01% under front and back illumination conditions, respectively. The back/front efficiency ratio is very promising for efficient bifacial DSSCs.

Manganese Oxide Nanoparticle as a New p-Type Dopant for High-Performance Polymer Field-Effect Transistors.

We report a new p-type dopant, manganese oxide (Mn3O4) nanoparticle, to enhance the performance of organic field-effect transistors (OFETs) with conjugated polymers, including poly(3-hexylthiophene-2,5-diyl), poly[[N,N 9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)], and poly[[2,5-bis(2-octyldodecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2'-(2,5-thiophene)bis-thieno(3,2b) thiophene]-5,5'-diyl]] (DPPT-TT). Incorporating a small amount of Mn3O4 nanoparticles in the semiconductor film significantly improved the hole mobility and decreased the threshold voltage for all OFETs, indicating efficient Mn3O4 nanoparticle p-type doping. The Mn3O4 nanoparticle showed a better doping efficiency than the widely used FeCl3 dopant due to better mixability with the host conjugated polymers. In particular, doped DPPT-TT OFETs showed significantly improved mobility up to 2.35 (±0.4) cm2/(V·s) with enhanced air and operational stability at 0.1 wt % doping concentration from 1.2 cm2/(V·s) for pristine devices.

Universal diffusion-limited injection and the hook effect in organic thin-film transistors.

The general form of interfacial contact resistance was derived for organic thin-film transistors (OTFTs) covering various injection mechanisms. Devices with a broad range of materials for contacts, semiconductors, and dielectrics were investigated and the charge injections in staggered OTFTs was found to universally follow the proposed form in the diffusion-limited case, which is signified by the mobility-dependent injection at the metal-semiconductor interfaces. Hence, real ohmic contact can hardly ever be achieved in OTFTs with low carrier concentrations and mobility, and the injection mechanisms include thermionic emission, diffusion, and surface recombination. The non-ohmic injection in OTFTs is manifested by the generally observed hook shape of the output conductance as a function of the drain field. The combined theoretical and experimental results show that interfacial contact resistance generally decreases with carrier mobility, and the injection current is probably determined by the surface recombination rate, which can be promoted by bulk-doping, contact modifications with charge injection layers and dopant layers, and dielectric engineering with high-k dielectric materials.