Side Chain Effects on the Conductivity of Phenothiazine-Derived Polyaniline

Side chain alkyl groups have become the standard for incorporating solubilizing groups into conjugated polymers. However, the variety of alkyl groups available and their location on the polymer’s backbone can contribute to the packing of the polymer chains in many different ways, resulting in many different morphologies in the polymer that can affect its properties and performances. In this paper, we investigate the effects on the conductivity of nine phenothiazine-containing polyaniline derivatives (P1–P9) with alkyl or aryl side chains on the phenothiazine core while also varying the number of methyl groups on the p-phenylenediamine unit. 1H nuclear magnetic resonance spectroscopy, ultraviolet–visible spectroscopy, differential scanning calorimetry, scanning electron microscopy, atomic force microscopy, and wide-angle X-ray scattering (WAXS) were all used to study the polymers’ structures, physical and thermal properties, and morphologies. The t-butylphenyl substituent on the phenothiazine core seems to provide more rigidity in the polymer’s backbone resulting in higher Tg for series 3, while series 2 containing the 2-hexyldecyl-substituted polymers had the lowest Tg, which is attributed to the large volume of the side chain, that limits interchain interactions. Consequently, series 2 had the lowest conductivity. However, the strongest effect on the conductivity was seen from the tetramethyl groups on the PPDA unit, which resulted in the lowest conductivity in each series due to torsional strain (twisting) in the polymer’s backbone. The WAXS data suggest mostly amorphous films; thus, the conductivity in these materials seems to be dominated by a multiscale charge transport phenomenon that occurs in amorphous conjugated materials. Our results will aid in the understanding of side chain engineering of PANI derivatives for their optimum performances

Variable-Temperature Scattering and Spectroscopy Characterizations for Temperature-Dependent Solution Assembly of PffBT4T-Based Conjugated Polymers

The solution structure of conjugated polymers (CPs) from which the films are cast is critical for tailoring the thin-film morphology thus device performance. Here, we used multimodal variable-temperature scattering and spectroscopy tools to fully quantify the solution assembly of poly­[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-dialkyl-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T) polymers with varying side-chain lengths at different assembly temperatures. The conformational and aggregation behaviors for PffBT4T-based CPs were found to be very sensitive to both temperature and side chain length using ultraviolet–visible (UV–vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). We found that with slightly increasing side chain length from 2-octyldodecyl (C8C12) to 2-nonyltridecyl (C9C13), PffBT4T-based CPs show a significant decrease in aggregation-to-dissolved chain transition temperature (10 °C), degree of aggregation, enthalpy change of aggregation, and size of the aggregates in solution. At room temperature, PffBT4T polymer strongly aggregated to form fabric structure with the film thickness of a few nanometers in thickness and hundreds of nanometers in length, as probed by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and dynamic light scattering (DLS). At the elevated temperature above the aggregation-to-dissolved chain transition temperature, PffBT4T is fully dissolved and adopts a semiflexible coil conformation with the persistence length of 3.1 nm for PffBT4T-C8C12 and a slightly increased persistence length of 3.4 nm for PffBT4T-C9C13, according to temperature-dependent SANS measurements. Longer side chains of PffBT4T-C9C13 also lead to less aggregation enthalpy gain compared with PffBT4T-C8C12. This work provides a solution structure manipulating strategy of CPs and thus will inspire the molecular design and processing protocols of CPs toward higher performance electronic devices

Effects of Poly(3-hexylthiophene) Molecular Weight and the Aging of Spinning Solution on the Electrospun Fiber Properties

The electrospinning technique is an attractive route for processing conjugated polymers in a significant quantity for large-scale applications. However, the processing–structure–property relationship of the electrospinning process for conjugated polymers is not well understood. Here, we report the electrospinning of poly(3-hexylthiophene) (P3HT) for three different molecular weights of P3HT: 31, 58, and 83 kDa. Chloroform was used as a solvent, and a high molecular weight poly(ethylene oxide) (PEO) was utilized to facilitate the processing of P3HT. Electrospinning was performed on the freshly prepared and 24 h aged spinning solutions. The aging of the spinning solution led to the self-assembly of P3HT chains, particularly with dominant H-aggregation for 83 kDa P3HT. The structure development and properties of the fibers were investigated, including the single-fiber electrical conductivity measured using a custom-built setup. Electrical conductivity has been found to increase with increasing molecular weight, and as high as a fivefold enhancement in single-fiber electrical conductivity was obtained for the fibers from the aged solution compared to the fiber from the freshly prepared solution. Despite a 25% PEO concentration in the fibers, the maximum electrical conductivity of a single fiber was found to be ≈2.7 × 10–5 S/cm, similar to the pristine P3HT thin films. Our study provides an additional understanding of P3HT structure development in electrospun fibers as a function of polymer molecular weight and processing steps and relates that to fiber properties

First fossil evidence for a new frog from the Early Cretaceous of the Jiuquan Basin, Gansu Province, north-western China

Based on a well-preserved incomplete skeleton, a new frog, Gansubatrachus qilianensis gen. et sp. nov., is described from the Lower Cretaceous Zhonggou Formation of Jiuquan Basin, Gansu Province, north-western China. This species differs from other frogs in a unique combination of characteristics, such as a robust and non-bifurcated alary process on the premaxilla, a ‘V’-shaped parahyoid, a paired sphenethmoid, eight presacral vertebrae, three pairs of free ribs, and unexpanded sacral diapophyses. Phylogenetic analysis based on parsimony suggests that Gansubatrachus is a basal Lalagobatrachia. This discovery of a new frog fossil from the Early Cretaceous of north-west China expands the diversity of fossil frogs in East Asia and provides new material for further studies on the distribution and evolutionary history of Cretaceous Asian anurans. http://zoobank.org/urn:lsid:zoobank.org:pub:A80B417A-F9C6-4704-B473-FBBA6CDC8C2B</p

Impact of Molecular Design on Degradation Lifetimes of Degradable Imine-Based Semiconducting Polymers

Transient electronics are a rapidly emerging field due to their potential applications in the environment and human health. Recently, a few studies have incorporated acid-labile imine bonds into polymer semiconductors to impart transience; however, understanding of the structure–degradation property relationships of these polymers is limited. In this study, we systematically design and characterize a series of fully degradable diketopyrrolopyrrole-based polymers with engineered sidechains to investigate the impact of several molecular design parameters on the degradation lifetimes of these polymers. By monitoring degradation kinetics via ultraviolet–visible spectroscopy, we reveal that polymer degradation in solution is aggregation-dependent based on the branching point and Mn, with accelerated degradation rates facilitated by decreasing aggregation. Additionally, increasing the hydrophilicity of the polymers promotes water diffusion and therefore acid hydrolysis of the imine bonds along the polymer backbone. The aggregation properties and degradation lifetimes of these polymers rely heavily on solvent, with polymers in chlorobenzene taking six times as long to degrade as in chloroform. We develop a new method for quantifying the degradation of polymers in the thin film and observe that similar factors and considerations (e.g., interchain order, crystallite size, and hydrophilicity) used for designing high-performance semiconductors impact the degradation of imine-based polymer semiconductors. We found that terpolymerization serves as an attractive approach for achieving degradable semiconductors with both good charge transport and tuned degradation properties. This study provides crucial principles for the molecular design of degradable semiconducting polymers, and we anticipate that these findings will expedite progress toward transient electronics with controlled lifetimes

Strain-Induced Nanocavitation in Block Copolymer Thin Films for High Performance Filtration Membranes

A new pore formation process was investigated for the manufacture of composite ultrafiltration membranes. Phase-separated block copolymer (BCP) thin films supported on a compliant macroporous poly­(ether sulfone) (PES) support craze under tensile strain, leaving behind pores of predictable size based on the self-assembled nanoscopic domains. The high aspect ratio pores formed in this process were used to create membranes that were highly permeable (959 L/(m2 h bar) with near complete rejection of 40 nm diameter gold nanoparticles (AuNP). By use of BCP’s inherent ability to cavitate under strain, tedious block removal steps are avoided. Membranes can thus be prepared in a simple, roll-to-roll ready, one-step process. In this initial study, BCP craze formation and filtration performance were characterized for various polymer types, molecular weights, and thicknesses. All these factors influenced the BCP’s thin film morphology, mechanical performance, deformation mechanism, and ultimately filtration performance. This work demonstrates a possible new path toward achieving scalable, BCP-based ultrafiltration membranes

Efficient and Stable Self-Passivation Perovskite Solar Cells Prepared in Ambient Air Based on an Antisolvent-Free Method

Solution processable perovskite solar cells (PSCs) are one of the most promising candidates for commercialization. However, the perovskite film preparation method is limited by the mandatory antisolvent process under an inert gas atmosphere which significantly influenced its mass production. In this study, we developed a perovskite film preparation without the requirement of antisolvent dripping in air. We employed various solvents to prepare perovskite films and studied their influence on perovskite nucleation and morphology for the respective solvents. Among them, the perovskite prepared using dimethylacetamide (DMAc), which has low solubility and high interaction with PbI2, demonstrated a highly crystalline perovskite black phase without antisolvent dripping. Furthermore, we found that the perovskite concentration played an important role in the perovskite film quality, where the high concentration DMAc-based perovskite produced a smooth and dense perovskite film by the antisolvent-free method in air. PSCs fabricated using this technique delivered a champion power conversion efficiency (PCE) of 20.1%. At the same time, the best device prepared by the blade-coated method also got 18% PCE. Moreover, the unencapsulated devices exhibited excellent stability, which retained more than 90% of their initial efficiency after 47 days in air. This work provides a facile and cost-effective method toward a controllable fabrication of high-performance antisolvent-free MAPbI3-based solar cells

Strong Acceptor Annulation Enables Control of Electronic Structure and Spin Configuration in Donor–Acceptor Conjugated Polymers

Open-shell conjugated polymers (CPs) offer new opportunities to integrate the spin degree of freedom within emerging technologies. Central to their realization are strong acceptors that stabilize unpaired spins within the π-conjugated backbones. Here, we demonstrate a high-spin CP composed of alternating benzo[1,2-b:4,5-b′]dithiophene donors and a new, strongly electron-withdrawing 6,7,8,9-tetrachloro-[1,2,5]thiadiazolo[3,4-b]phenazine acceptor. A comparative study with a 6,7-dimethyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) acceptor demonstrates that annulation and chlorination of the TQ framework facilitates a transition between closed-shell aromatic and high-spin quinoidal forms. This is accompanied by a concomitant reduction of the bandgap, high electron affinity, delocalization of spin density, and n-type conduction. These insights enable access to a broader range of open-shell CPs and the manipulation of important properties such as topology, exchange interactions, and carrier polarity

Efficient and Stable Self-Passivation Perovskite Solar Cells Prepared in Ambient Air Based on an Antisolvent-Free Method

Solution processable perovskite solar cells (PSCs) are one of the most promising candidates for commercialization. However, the perovskite film preparation method is limited by the mandatory antisolvent process under an inert gas atmosphere which significantly influenced its mass production. In this study, we developed a perovskite film preparation without the requirement of antisolvent dripping in air. We employed various solvents to prepare perovskite films and studied their influence on perovskite nucleation and morphology for the respective solvents. Among them, the perovskite prepared using dimethylacetamide (DMAc), which has low solubility and high interaction with PbI2, demonstrated a highly crystalline perovskite black phase without antisolvent dripping. Furthermore, we found that the perovskite concentration played an important role in the perovskite film quality, where the high concentration DMAc-based perovskite produced a smooth and dense perovskite film by the antisolvent-free method in air. PSCs fabricated using this technique delivered a champion power conversion efficiency (PCE) of 20.1%. At the same time, the best device prepared by the blade-coated method also got 18% PCE. Moreover, the unencapsulated devices exhibited excellent stability, which retained more than 90% of their initial efficiency after 47 days in air. This work provides a facile and cost-effective method toward a controllable fabrication of high-performance antisolvent-free MAPbI3-based solar cells

FAPbI₃ Perovskite Films Prepared by Solvent Self-Volatilization for Photovoltaic Applications

Developing a simple method to synthesize the perovskite layer without the antisolvent technique can facilitate the industrial production of perovskite solar cells (PSCs). Limited progress has been made for the antisolvent-free method on formamidinium lead triiodide perovskite layers because of the phase stability issue. Here, we use N-methyl pyrrolidone (NMP) as an additive to inhibit the nonperovskite phase of FAPbI3 to fabricate the formamidinium iodide (FAI)–PbI2–NMP intermediate phase via the self-volatilization of volatile solvent 2-methoxyethanol instead of the traditional antisolvent method. The high-quality pure α phase of FAPbI3 films is obtained by phase transition via annealing. The photovoltaic properties of the perovskite films affected by different NMP amounts are studied. The corresponding PSCs show a PCE of 20.1% compared to 15.6% for the PSCs fabricated with the classical antisolvent technique. The unencapsulated devices exhibit ∼75% efficiency of their initial PCE values after 35 days of storage. This method can be used in the scalable production of PSCs because of high reproducibility and easy operation