Non-chlorinated Solvents Research Articles

Fluorescent Aromatic Polyether Sulfones: Processable, Scalable, Efficient, and Stable Polymer Emitters and Their Single-Layer Polymer Light-Emitting Diodes.

In this study, fully aromatic polyether sulfones were developed, bearing blue, yellow, and orange-red π-conjugated semiconducting units. Carbazole-, anthracene-, and benzothiadiazole-based fluorophores are copolymerized with a diphenylsulfone moiety. A diphenylpyridine comonomer was additionally utilized, acting as both a solubilizing unit and a weak blue fluorescent group. Using this rationale, fluorescent polyarylethers with high molecular weights, up to 70 kDa, were developed, showing film formation ability and high thermal stability, while preserving excellent solubility in common organic, nonvolatile, and nonchlorinated solvents. Fine-tuning of the emission color was achieved through subtle changes of the comonomers' type and ratio. Single-chromophore-bearing copolymers emitted in the blue or the yellow region of the visible spectrum, while the dual-chromophore-bearing terpolymers emitted throughout the visible spectrum, resulting in white light emission. Solutions of 20 wt% in polar aprotic solvents at ambient conditions allowed the deposition of fluorescent copolyethers and printing from non-chlorinated solvents. All polyethers were evaluated for their structural and optoelectronic properties, and selected copolymers were successfully used in the emitting layer (EML) of organic light-emitting diode (OLED) devices, using either rigid or flexible substrates. Remarkable color stability was displayed in all cases for up to 15 V of bias voltage. The Commission Internationale de L'Eclairage (CIE) of the fabricated devices is located in the blue (0.16, 0.16), yellow (0.44, 0.50), or white region of the visible spectrum (0.33, 0.38) with minimal changes according to the ratio of the comonomers. The versatile methodology toward semiconducting polyethersulfones for polymer light-emitting diodes (PLEDs) developed herein led to the scaled-up production of luminescent polymers of up to 25 g of high-molecular-weight single batches, demonstrating the effectiveness of this approach as a straightforward tool to facilitate the synthesis of flexible and printable EMLs for large-area PLED coverage.

Chemical recycling of bromine-terminated polymers synthesized by ATRP.

Chemical recycling of polymers is one of the biggest challenges in materials science. Recently, remarkable achievements have been made by utilizing polymers prepared by controlled radical polymerization to trigger low-temperature depolymerization. However, in the case of atom transfer radical polymerization (ATRP), depolymerization has nearly exclusively focused on chlorine-terminated polymers, even though the overwhelming majority of polymeric materials synthesized with this method possess a bromine end-group. Herein, we report an efficient depolymerization strategy for bromine-terminated polymethacrylates which employs an inexpensive and environmentally friendly iron catalyst (FeBr2/L). The effect of various solvents and the concentration of metal salt and ligand on the depolymerization are judiciously explored and optimized, allowing for a depolymerization efficiency of up to 86% to be achieved in just 3 minutes. Notably, the versatility of this depolymerization is exemplified by its compatibility with chlorinated and non-chlorinated solvents, and both Fe(ii) and Fe(iii) salts. This work significantly expands the scope of ATRP materials compatible with depolymerization and creates many future opportunities in applications where the depolymerization of bromine-terminated polymers is desired.

Green-Processed Non-Fullerene Organic Solar Cells Based on Y-Series Acceptors.

The development of environmentally friendly and sustainable processes for the production of high-performance organic solar cells (OSCs) has become a critical research area. Currently, Y-series electron acceptors are widely used in high-performance OSCs, achieving power conversion efficiencies above 19%. However, these acceptors have large fused conjugated backbones that are well-soluble in halogenated solvents, such as chloroform and chlorobenzene, but have poor solubility in non-halogenated green solvents. To overcome this challenge, recent studies have focused on developing green-processed OSCs that use non-chlorinated and non-aromatic solvents to dissolve bulk-heterojunction photoactive layers based on Y-series electron acceptors, enabling environmentally friendly fabrication. In this comprehensive review, an overview of recent progress in green-processed OSCs based on Y-series acceptors is provided, covering the determination of Hansen solubility parameters, the use of non-chlorinated solvents, and the dispersion of conjugated nanoparticles in water/alcohol. It is hoped that the timely review will inspire researchers to develop new ideas and approaches in this important field, ultimately leading to the practical application of OSCs.

PNP]-Stabilized Niobium(IV) and Tantalum(IV) Complexes: Synthesis and Characterization of an Open-Shell Tantalum Alkylidene

A flexible [PNP] ligand (forming six-membered chelates upon coordination) was employed for the synthesis of niobium(IV) and tantalum(IV) complexes. Starting from the protioligand (H[PNP]) and the tetrachlorides NbCl4(thf)2 or TaCl4, the trichloro complexes [PNP]MCl3 (1-M, M = Nb, Ta) were prepared via in situ deprotonation using LiN(SiMe3)2. Attempts to alkylate complexes 1-M (M = Nb, Ta), however, were impeded due to their limited solubility in nonchlorinated solvents. Hence, the lithiated ligand was reacted with (thf)2Cl3M=CHCMe2Ph (M = Nb, Ta) to afford the d0-configured alkylidene complexes 2-Nb and 2-Ta, respectively. These meridionally coordinated and freely soluble complexes were found to be stable in nonchlorinated and chlorinated solvents, even at elevated temperature. Reduction of compounds 2-M with magnesium anthracene (2-Nb and 2-Ta) or sodium naphthalide (2-Ta) afforded the corresponding d1-configured alkylidenes (3-Nb and 3-Ta), although the reduced niobium derivative was found to decompose rapidly. A 10-line and an 8-line EPR pattern was detected for 3-Nb (I(93Nb) = 9/2) and 3-Ta (I(181Ta) = 7/2), respectively, confirming the metalloradical character of each complex. For 3-Ta, the molecular structure was elucidated by single crystal X-ray diffraction. With the molecular structure of this d1-configured (open-shell) tantalum alkylidene ascertained, its electronic structure was examined by DFT and CASSCF calculations.

A polymer library enables the rapid identification of a highly scalable and efficient donor material for organic solar cells.

The dramatic improvement of the PCE (power conversion efficiency) of organic photovoltaic devices in the past few years has been driven by the development of new polymer donor materials and non-fullerene acceptors (NFAs). In the design of such materials synthetic scalability is often not considered, and hence complicated synthetic protocols are typical for high-performing materials. Here we report an approach to readily introduce a variety of solubilizing groups into a benzo[c][1,2,5]thiadiazole acceptor comonomer. This allowed for the ready preparation of a library of eleven donor polymers of varying side chains and comonomers, which facilitated a rapid screening of properties and photovoltaic device performance. Donor FO6-T emerged as the optimal material, exhibiting good solubility in chlorinated and non-chlorinated solvents and achieving 15.4% PCE with L8BO as the acceptor (15.2% with Y6) and good device stability. FO6-T was readily prepared on the gram scale, and synthetic complexity (SC) analysis highlighted FO6-T as an attractive donor polymer for potential large scale applications.

Boosting electron transport in non-fullerene acceptors using non-chlorinated solvents

Chlorinated solvents are commonly used to process organic semiconductor devices but have several negative environmental impacts.

Star-shape non-fullerene acceptor featuring an aza-triangulene core for organic solar cells.

We present the simple synthesis of a star-shape non-fullerene acceptor (NFA) for application in organic solar cells. This NFA possesses a D(A)3 structure in which the electron-donating core is an aza-triangulene unit and we report the first crystal structure for a star shape NFA based on this motive. We fully characterized this molecule's optoelectronic properties in solution and thin films, investigating its photovoltaic properties when blended with PTB7-Th as the electron donor component. We demonstrate that the aza-triangulene core leads to a strong absorption in the visible range with an absorption edge going from 700 nm in solution to above 850 nm in the solid state. The transport properties of the pristine molecule were investigated in field effect transistors (OFETs) and in blends with PTB7-Th following a Space-Charge-Limited Current (SCLC) protocol. We found that the mobility of electrons measured in films deposited from o-xylene and chlorobenzene are quite similar (up to 2.70 × 10-4 cm2 V-1 s-1) and that the values are not significantly modified by thermal annealing. The new NFA combined with PTB7-Th in the active layer of inverted solar cells leads to a power conversion efficiency of around 6.3% (active area 0.16 cm2) when processed from non-chlorinated solvents without thermal annealing. Thanks to impedance spectroscopy measurements performed on the solar cells, we show that the charge collection efficiency of the devices is limited by the transport properties rather than by recombination kinetics. Finally, we investigated the stability of this new NFA in various conditions and show that the star-shape molecule is more resistant against photolysis in the presence and absence of oxygen than ITIC.

Near-ultraviolet emitters based on carbazole-imidazole for highly efficient solution-processed organic light-emitting diodes

Solution-processable near-ultraviolet (NUV) and deep-blue organic emitters are crucial for the development of organic light-emitting diodes (OLEDs) in large-area production. However, such wide band gap materials with high photoluminescence quantum yield (PLQY) and stable electroluminescence are sparse. Here, three NUV and deep-blue solution-processable emitters, carbazole-imidazole derivatives, BuCzI, BuCzI-CN and BuCzI-BCN, are synthesized by employing 3,6-di-tert-butyl-carbazole at N1 position of imidazole as electron donor to construct a twisted and rigid structure of donor-linker-acceptor. The combination of carbazole and imidazole fulfills saturated NUV and deep-blue emission in solution and film, accompanied with excellent solubility in non-chlorinated solvents. Furthermore, the bulky donor of 3,6-di-tert-butyl-carbazole not only enhances localized excited and keeps high PLQY in different solvents, but also suppresses emission red-shift which results from intramolecular charge transfer (ICT) to realize NUV emission. The solution-processed undoped OLEDs fabricated with BuCzI, BuCzI-CN and BuCzI-BCN as emitters achieve external quantum efficiency (EQE) up to 3.30 %, 2.20 % and 2.63 % with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.15, 0.04), (0.15, 0.06) and (0.15, 0.09), respectively. All devices retain stable NUV and deep-blue emission at varied applying voltages. The results of this work have provided a novel design strategy for NUV solution-processable organic emitters with high efficiency and stability.

A tailored fast thioacidolysis method incorporating multi-reaction monitoring mode of GC-MS for higher sensitivity on lignin monomer quantification

Abstract Thioacidolysis is widely used for lignin structural characterization by cleaving β-aryl ethers to release syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) monomers followed by GC analysis. However, the traditional thioacidolysis method requires tedious extraction steps with chlorinated solvent underlying harmful to health, limiting its efficiency and application. Herein, an improved thioacidolysis method with high sensitivity for the quantitation of lignin-derived monomers was developed. The improved protocol used a quick, streamlined procedure to recover the monomeric products using ethyl acetate as extracting solvent and MS detector in multi-reaction monitoring mode to enhance its ability to detect extremely low concentration (0.1 ppb with signal-to-noise higher than 2) of monomeric products. Additionally, a fast GC program was established to speed up the GC quantitation. Several representative lignocellulose samples, including gymnosperm, angiosperm, and poaceae, were used to test this tailored method. The results demonstrated that the ratios of lignin monomer compositions determined by this method were consistent with that of traditional procedure despite the slightly higher monomer yields measured. More importantly, this method uses non-chlorinated solvent for microscale extraction and requires no evaporation step for workup, which is a green and efficient way for the quantification of lignin monomer compositions.

Extraction of Polyhydroxyalkanoates from Purple Non-Sulfur Bacteria by Non-Chlorinated Solvents.

In this study, non-chlorinated solvents such as cyclohexanone (CYC) and three ionic liquids, (ILs) (1-ethyl-3-methylimidazolium dimethylphosphate, [EMIM][DMP], 1-ethyl-3-methylimidazolium diethylphosphate, [EMIM][DEP] and 1-ethyl-3-methylimidazolium methylphosphite, [EMIM][MP]) were tested to extract polyhydroxyalkanoates (PHAs) from the purple non-sulfur photosynthetic bacterium (PNSB) Rhodovulum sulfidophilum DSM-1374. The photosynthetic bacterium was cultured in a new generation photobioreactor with 4 L of working volume using a lactate-rich medium. The extracted PHAs were characterized using a thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy, proton nuclear magnetic resonance and gel permeation chromatography. The most promising results were obtained with CYC at 125 °C with an extraction time of above 10 min, obtaining extraction yields higher than 95% and a highly pure poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) with around 2.7 mol% of hydroxylvalerate (HV). A similar yield and purity were obtained with chloroform (CHL) at 10 °C for 24 h, which was used as the referent solvent Although the three investigated ILs at 60 °C for 4 and 24 h with biomass/IL up to 1/30 (w/w) obtained PHAs strongly contaminated by cellular membrane residues, they were not completely solubilized by the investigated ILs.

A nonchlorinated solvent-processed polymer semiconductor for high-performance ambipolar transistors.

Ambipolar polymer semiconductors are potentially serviceable for logic circuits, light-emitting field-effect transistors (LFETs) and polymer solar cells (PSCs). Although several high-performance ambipolar polymers have been developed, their optoelectronic devices are generally processed from toxic chlorinated solvents. To achieve the commercial applications of organic FETs (OFETs), the polymers should be processed from nonchlorinated solvents, instead of chlorinated solvents. However, most conjugated polymers show poor solubility in nonchlorinated solvents. It is of great importance to develop ambipolar polymers that can be processed from nonchlorinated solvents. Here, we develop a nonchlorinated solvent processed polymer named poly[7-fluoro-N, N′-di(4-decyltetradecyl)-7′-azaisoindigo-6′,6″-(thieno[3,2-b]thiophene-2,5-diyl)-7‴-fluoro-N″, N‴-di(4-decyltetradecyl)-7″-azaisoindigo-6,6‴-([2,2″-bithiophene]-5,5″-diyl)] (PITTI-BT) by designing a monomer with a large molar mass. The polymer displays good solubility in p-xylene (PX). Well-aligned films of PITTI-BT are achieved by an off-center spin-coating (SC) method. Based on the high-quality films, the OFETs fabricated from PX solution achieve record ambipolar performance with hole and electron mobilities of 3.06 and 2.81 cm2 V−1 s−1, respectively. The combination of nonchlorinated solvents and good alignment process offers an effective and eco-friendly approach to obtain high-performance ambipolar transistors.

Nonchlorinated Solubility Enhanced by Lipophilicity: An Effective Strategy for Environmentally Benign Processing of Rigidly Regular n‐type Polymeric Semiconductors

AbstractApplication of high‐performance unipolar n‐type polymeric semiconductors lagged behind due to those polymers’ poor solubility in green solvents. Traditional methods, such as random copolymerization and asymmetric structuring, enhance solubility but reduce mobility. Here, a universal “lipophilicity strategy” for eco‐friendly processing is reported. This strategy could effectively improve the solubility of polymers without sacrificing crystallinity thus maintaining good mobility of the devices. CF3 group and SCF3 group, which are famous for their high lipophilicity, are introduced to (E)‐1,2‐di(thiophen‐2‐yl)ethane (TVT). The solubility of two monomers is confirmed to be 5 and 16 times higher than the brominated counterpart, respectively. Moreover, CF3TVT and SCF3TVT not only improve solubility of the polymers but also reduce energy levels of donor unit due to their strong electron withdrawing property. By using Ozawa's condition, three unipolar n‐type semiconducting polymers are obtained through direct (hetero)arylation polycondensation (DHAP). Among them, CF3TVT based P2 processed by xylene solutions exhibited the best unipolar n‐type mobility up to 1.37 cm2 V−1 s−1 and reached current on/off ratio of 108, for the first time realizing both green synthesis and nonchlorinated processing. In general, this lipophilicity strategy provides an effective guideline to design high‐performance n‐type polymer with good solubility in nonchlorinated solvents.

Photoactive Material for Highly Efficient and All Solution‐Processed Organic Photovoltaic Modules: Study on the Efficiency, Stability, and Synthetic Complexity

A scalable and accessible photoactive formulation with a low synthetic complexity (SC) index is utilized in organic photovoltaic (OPV) fabrication. The formulation readily dissolves in nonchlorinated solvents, and the corresponding photoactive films can be processed by various coating methods to fabricate devices with power conversion efficiencies (PCEs) of 16.1% and 15.2% when using vacuum‐based molybdenum oxide and solution‐processable conducting polymer as the hole transporting layer in the inverted structure, respectively. This prepared device shows superior stability under light exposure. The PCE is maintained 94% of the initial values after 1080 h of light soaking at 100 mW cm−2. Furthermore, the figure of merit based on the ratio of the SC index and PCE indicates the benefit of this formulation for OPV manufacturing, showing the feasibility of commercialization. Eventually, a PCE of 10.3% is demonstrated for a mini‐module fabricated under ambient conditions, with an active area of 32.6 cm2. To our knowledge, this PCE is one of the largest values reported to date for a green solvent and an all‐solution‐processed OPV module with an inverted architecture.

Constructing a new polymer acceptor enabled non-halogenated solvent-processed all-polymer solar cell with an efficiency of 13.8.

A new polymer acceptor, PS1, was developed by connecting the non-fullerene acceptor building block of dithienothiophen[3,2-b]pyrrolobenzotriazole capped with 3-(dicyanomethylidene)-indan-1-one through a thiophene spacer. The solubilizing alkyl side groups in the central unit enabled PS1 to be readily dissolved in non-chlorinated solvents. By using 2-methyltetrahydrofuran as the processing solvent, the all-polymer solar cell (all-PSC) containing PS1 and a polymer donor PTzBI-oF in the light-harvesting layer exhibited an impressively high power conversion efficiency of 13.8%.

N-Substituted Phenothiazines as Environmentally Friendly Hole-Transporting Materials for Low-Cost and Highly Stable Halide Perovskite Solar Cells.

Most of the high-performing halide perovskite solar cells (PSCs) leverage toxic chlorinated solvents (e.g., o-dichlorobenzene or chlorobenzene) for the hole-transporting material (HTM) processing and/or antisolvents in the perovskite film fabrication. To minimize the environmental and health-related hazards, it is highly desirable, yet at the same time demanding, to develop HTMs and perovskite deposition processes relying on nonhalogenated solvents. In this work, we designed two small molecules, AZO-III and AZO-IV, and synthesized them via simple and environmentally friendly Schiff base chemistry, by condensation of electron-donating triarylamine and phenothiazine moieties connected through an azomethine bridge. The molecules are implemented as HTMs in PSCs upon processing in a nonchlorinated (toluene) solvent, rendering their synthesis and film preparation eco-friendly. The enhancement in the power conversion efficiency (PCE) was achieved when switching from AZO-III (9.77%) to AZO-IV (11.62%), in which the thioethyl group is introduced in the 2-position of the phenothiazine ring. Additionally, unencapsulated PSCs based on AZO-III displayed excellent stabilities (75% of the initial PCEs is retained after 6 months of air exposure for AZO-III to be compared with a 48% decrease of the initial PCE for Spiro-OMeTAD-based devices). The outstanding stability and the extremely low production cost (AZO-III = 9.23 $/g and AZO-IV = 9.03 $/g), together with the environmentally friendly synthesis, purification, and processing, make these materials attractive candidates as HTMs for cost-effective, stable, and eco-friendly PSCs.

Azaisoindigo-Based Polymers with a Linear Hybrid Siloxane-Based Side Chain for High-Performance Semiconductors Processable with Nonchlorinated Solvents.

Developing nonchlorinated solvent-processed polymeric semiconductors to avoid environmental concerns and health hazards caused by chlorinated solvents is especially urgent. Here, a molecular design strategy, composed of backbone fluorination and side chain optimization, is used for preparing high-solubility and high-performance azaisoindigo-based polymers. The effects of different backbones and side chains on the solubility, film crystallinity, molecular stacking, and charge transport properties are mainly investigated. A long linear hybrid siloxane-based chain (C6-Si7) is chosen to improve the solubility, while the incorporation of fluorine (F) is used to enhance the film crystallinity and charge mobility. By optimizing the backbone and side chain, both solubility and charge mobility of the azaisoindigo-based polymer are significantly improved. As a result, PAIIDBFT-Si films processed with toluene, tetrahydrofuran, ether, and alkanes, achieved charge mobilities of 4.14, 3.78, 2.14, and 2.34 cm2 V-1 s-1, respectively. The current study provides an effective strategy for the design and synthesis of high-performance polymeric semiconductors processed with nonchlorinated solvents.

Solution‐Processed, Insoluble Thin Films through In Situ Chemical Polymerization of Semiconducting Native Polythiophene

The use of multilayer, solution‐processed organic thin film devices can benefit strongly from the controlled deposition of insoluble thin films. Here, a solution‐based in situ polymerization technique for semiconducting polythiophene thin films based on nonchlorinated solvents forming a range of large‐scale structured or homogeneous, insoluble thin films is systematically developed. The high‐quality nature of the resulting polythiophene thin films is demonstrated by successfully implementing the films in the active layer of bilayer heterojunction solar cells. It is possible to transfer this protocol to large‐scale processing without additional changes to the material system.

Methyl functionalization on conjugated side chains for polymer solar cells processed from non-chlorinated solvents

Methyl functionalization on conjugated thiophene side chains is developed as an effective fine-tuning approach for polymeric donors, affording substantial efficiency improvement for polymer solar cells processed from non-chlorinated solvents.

Acceptor–donor–acceptor molecule processed using polar non-halogenated solvents for organic field-effect transistors

The polar non-chlorinated solvents were used as processed solvents for fabricating small molecule-based high-performance OFETs.

A Simple Structure Conjugated Polymer for High Mobility Organic Thin Film Transistors Processed from Nonchlorinated Solvent.

Herein, a simple structure, nonchlorinated solvent processable high mobility donor–acceptor conjugated polymer, poly(2,5‐bis(4‐hexyldodecyl)‐2,5‐dihydro‐3,6‐di‐2‐thienyl‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐alt‐thiophene) (PDPPT3‐HDO), is reported. The enhanced solubility in nonchlorinated solvent is realized based on a denser alkyl side chains strategy by incorporating small size comonomer thiophene. An associated benefit of thiophene comonomer is the remarkable structural simplicity of the resulting polymer, which is advantageous for industrial scaling up. The alkyl side chain density and structure of PDPPT3‐HDO can efficiently control the self‐assembly properties in solution and film. By bar coating from o‐xylene solution, PDPPT3‐HDO forms aligned films and exhibits high hole mobility of up to 9.24 cm2 V−1 s−1 in organic thin film transistors (OTFTs). Notably, the bar‐coated OTFT based on PDPPT3‐HDO shows a close to ideal transistor model and a high mobility reliability factor of 87%. The multiple benefits of increased side chain density strategy may encourage the design of high mobility polymers that meet the requirements of mass production of OTFT materials and devices.