Solvent Annealing Research Articles

Highly Ordered Porous Inorganic Structures via Block Copolymer Lithography: An Application of the Versatile and Selective Infiltration of the "Inverse" P2VP-b-PS System.

A facile and versatile strategy was developed to produce highly ordered porous metal oxide structures via block copolymer (BCP) lithography. Phase separation of poly(2-vinylpyridine)-b-polystyrene (P2VP-b-PS) was induced by solvent vapor annealing in a nonselective solvent environment to fabricate cylindrical arrays. In this work, we thoroughly analyzed the effects of the film thickness, solvent annealing time, and temperature on the ordering of a P2VP-majority system for the first time, resulting in "inverse" structures. Reflectometry, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy were used to characterize the formation of the highly ordered BCP morphology and the subsequently produced metal oxide film. At 40 min solvent annealing time, hexagonally close packed structures were produced with cylinder diameters ∼40 nm. Subsequently, the BCP films were infiltrated with different metal cations. Metal ions (Cr, Fe, Ni, and Ga) selectively infiltrated the P2VP domain, while the PS did not retain any detectable amount of metal precursor. This gave rise to a metal oxide porous structure after a UV/ozone (UVO) treatment. The results showed that the metal oxide structures demonstrated high fidelity compared to the BCP template and cylindrical domains presented a similar size to the previous PS structure. Moreover, XPS analyses revealed the complete elimination of the BCP template and confirmed the presence of the metal oxides. These metal oxides were used as hard masks for pattern transfer via dry etching as a further application. Silicon nanopores were fabricated mimicking the BCP template and demonstrated a pore depth of ∼50 nm. Ultimately, this strategy can be applied to create different inorganic nanostructures for a diverse range of applications, for example, solar cells, diodes, and integrated circuits. Furthermore, by optimizing the etching parameters, deeper structures can be obtained via ICP/RIE processes, leading to many potential applications.

Synthesis and self-assembly of polystyrene block polyacrylic acid for sub 10 nm feature size

To promote lithography in the semiconductor industry, self-assembling block copolymers are the most feasible and cost-effective option. To address the challenges of the semiconductor industry, including predesigned engineering plans and reduction of defects, the best way is to use the advantages of block copolymers. These advantages are pattern density multiplication, feature size uniformity improvement, reducing line edge roughness, cost reduction, reaching 10 nm resolution, and more. The research presented here shows that polystyrene block polyacrylic acid (PS-b-PAA) would be a good candidate for direct assembly to achieve below 10 nm and fewer defect patterns. Polystyrene block polymethyl acrylate copolymers were synthesized using ATRP. Hydrolysis resulted in di-block copolymers of PS-b-PAA with polydispersity indices (PDI) of less than 1.3. Samples were characterized by various techniques, including FT-IR, H-NMR, GPC, DSC, and rheometer. By applying the temperature sweep test, the order-disorder transition temperature of a sample was observed to be 157 °C in the Temperature Sweep Test of rheometer analysis. The samples were then self-assembled on wafer silicones, and the patterns were subjected to a variety of thermal treatments, including solvent annealing, microwave irradiation, and solvothermal annealing. AFM, TEM, and SAXS analyses were performed on samples. Microwave-assisted self-assembly annealing is known as a rapid way to reduce defects, while AFM images of solvothermal annealed samples reveal close competition between the two types of treatment. Self-assembled lamellae structures below 10 nm in diameter were studied.

Fabrication of Dimensional and Structural Controlled Open Pore, Mesoporous Silica Topographies on a Substrate.

Open pore mesoporous silica (MPS) thin films and channels were prepared on a substrate surface. The pore dimension, thickness and ordering of the MPS thin films were controlled by using different concentrations of the precursor and molecular weight of the pluronics. Spectroscopic and microscopic techniques were utilized to determine the alignment and ordering of the pores. Further, MPS channels on a substrate surface were fabricated using commercial available lithographic etch masks followed by an inductively coupled plasma (ICP) etch. Attempts were made to shrink the channel dimension by using a block copolymer (BCP) hard mask methodology. In this regard, polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin film forming perpendicularly oriented PEO cylinders in a PS matrix after microphase separation through solvent annealing was used as a structural template. An insitu hard mask methodology was applied which selectively incorporate the metal ions into the PEO microdomains followed by UV/Ozone treatment to generate the iron oxide hard mask nanopatterns. The aspect ratio of the MPS nanochannels can be varied by altering etching time without altering their shape. The MPS nanochannels exhibited good coverage across the entire substrate and allowed direct access to the pore structures.

Recent Advances in Bismuth‐Based Solar Cells: Fundamentals, Fabrication, and Optimization Strategies

AbstractSolar cells are star technologies in the utilization of renewable energy and have experienced tremendous development in the past few decades. Eco‐friendly processing technologies and materials to reduce the negative impacts and extend the lifetime of photovoltaics are becoming a very attractive research area. Bismuth triiodide, with its appropriate structure and suitable optoelectronic properties, has proved to be a low‐toxic and stable material for optoelectronic devices, and the best‐reported power conversion efficiencies (PCEs) are 1.50% for solar cells with BiI3 as photoactive layers and 5.56% for BiI3 based perovskite solar cells. Further developments in film fabrication and morphological control are necessary to improve the PCEs of bismuth‐based solar cells. In this review, the electronic structures and optical properties of bismuth halides materials are introduced to reveal their potential in solar cells. Then, different fabrication techniques including solvent engineering, solvent annealing, thermal engineering, and vapor phase fabrication are discussed. More importantly, the absorber layer optimization strategies and the interface engineering are summarized to improve performance of BiI3 solar cells. In the end, the challenges of BiI3 based solar cells and future research directions are discussed.

Macromolecule Relaxation Directed 3D Nanofiber Architecture in Stretchable Fibrous Mats for Wearable Multifunctional Sensors.

Elastomer fiber mat sensors, which are capable of perceiving mechanical stimuli, temperature, and vapor of chemicals, are highly desirable for designing wearable electronics and human-robot interfacing devices due to good wearability, skin affinity, and durability, and so on. However, it is still challenging to fabricate multiresponsive flexible wearable sensors with three-dimensional (3D) architecture using simple material and structure design. Herein, we report an all-in-one multiresponsive thermoplastic polyurethane (TPU) nanofiber mat sensors composed of crimped elastomer fibers with deposited platinum nanoparticles (PtNPs) on the fiber surface. The 1D TPU nanofibers could be transferred to nanofibers with different 3D nanofiber architectures by controllable macromolecular chain relaxation of aligned elastomer polymers upon poor solvent annealing. The conductive networks of PtNPs on wavy TPU fibers enable the sensor susceptible to multiple stimuli like strain/pressure, humidity, and organic vapors. Besides, the 3D nanofiber architectures allow the strain sensor to detect wider tensile strain and pressure with higher sensitivity due to delicate fiber morphology and structure control. Therefore, this work provides new insights into the fabrication of multifunctional flexible sensors with 3D architecture in an easy way, advancing the establishment of a multiple signal monitoring platform for the health care and human-machine interfacing.

0D/2D Mixed Dimensional Lead-Free Caesium Bismuth Iodide Perovskite for Solar Cell Application.

Bismuth-based perovskites are potentially a promising alternative for lead-free perovskites. During bond formation, however, trivalent ions on with CsI/BiI3 ratio of 1.5/1 form 0D-neutral charged compounds with higher bandgap (>2.0 eV) and poor absorption capacity. Mixed 0/2-dimensional structures are potentially suitable substitutes due to their low bandgap. So far, the reported CsI/BiI3 ratios for 0D/2D structures are 1:1, 1:2 and 1:3. Herein, a new ratio of 1/1.5 is reported. Caesium bismuth iodide at a ratio of CsI/BiI3 of 1/1.5 was synthesised using a one-step processing method with/without solvent vapour annealing. During solvent annealing, a 1/4 (v/v) mixture of DMF/methanol was used as a solvent. The crystal structure formed at a ratio of 1/1.5 is more similar to 1.5/1 than to 1/3. The XRD pattern revealed additional characteristics peaks at 009, 012, 209 and 300, indicating the growth of another phase. The formed heterogeneous mixed 0D/2D structure has an extended light absorption capacity greater than 720 nm. Solvent vapour annealing improved film morphology by enhancing grain size and packing density. When cells with and without solvent vapour annealing are compared, the power conversion efficiency of caesium bismuth iodide increases from 0.26% without solvent annealing to 0.98% with solvent vapour annealing. This study establishes a new route for future research on crystal configuration, nomenclature, film and morphology, quality tailoring and applications toward the goal of lead-free perovskite solar cells.

Joule-Heating Annealing to Increase Organic Solar Cells Performance: A Comparative Study

In this work, we present our results on the influence of post-deposition treatments on the morphology and optical properties of photoactive films made of small molecules and their subsequent effect on the performance of photovoltaic (PV) devices. We have chosen DPP(TBFu)2:PC61BM as a benchmark model system and compared a novel joule-heating annealing (JHA) treatment with the widely used temperature annealing (TA) and solvent annealing (SVA) treatments. Detailed characterization of the morphology of the active layer and the performance of the devices suggests that JHA is a valuable post-treatment technique that provides fast information about the development of domains in the photoactive layer. Finally, in this context, solar cells on flexible indium tin oxide (ITO) substrates, made of polyethylene terephthalate (PET), were fabricated and analyzed.

Solvent Annealing of Striped Ellipsoidal Block Copolymer Particles: Reversible Control over Lamellae Asymmetry, Aspect Ratio, and Particle Surface.

Solvent annealing is a versatile tool to adjust the shape and morphology of block copolymer (BCP) particles. During this process, polar solvents are often used for block-selective swelling. However, such water-miscible solvents can induce (partial) solubilization of one block in the surrounding aqueous medium, thus, causing complex structural variations and even particle disassembly. To reduce the complexity in morphology control, we focused on toluene as a nonpolar polystyrene-selective solvent for the annealing of striped polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) ellipsoids. The selective stretching of PS chains produces unique asymmetric lamellae structures, which translate to an increase in the particle aspect ratio after toluene evaporation. Complete reversibility is achieved by changing to chloroform as a nonselective solvent. Moreover, surfactants can be used to tune block-selective wetting of the particle surface during the annealing; for example, a PS shell can protect the internal lamellae structure from disassembly. Overall, this versatile postassembly process enables the tailoring of the structural features of striped colloidal ellipsoids by only using commercial BCPs and solvents.

1 + 1 > 2: Dual strategies of quinolinic acid passivation and DMF solvent annealing for high-performance inverted perovskite solar cell

We developed a new combined method in which quinolinic acid (QA) passivation and DMF solvent annealing are carried out sequentially to enhance the performance of inverted perovskite solar cells. Upon systematic investigation, we found that: 1). One QA molecule not only passivates more than one defects within lattice or neighboring lattices, creating a multi-passivation effect, but also enhances the interactions between lattices, due to pyridine ring and dicarboxylic acid functional groups in the molecule; 2). By combining with DMF solvent annealing post-treatment sequentially, high quality perovskite films with very large grain size over 1 µm are obtained on the substrate of PEDOT: PSS. As a result, the PSC fabricated with the combined method demonstrates an excellent humidity stability and yields a PCE of 18.56% with 20% and 11.6% increment of Voc and Jsc, respectively. To the best of our knowledge, it is the highest reported PCE for inverted PSCs with undoped PEDOT:PSS as hole transporting layer. Therefore, our work indicates that the combined strategy of multi-passivation with QA and solvent annealing with DMF sequentially has a significant potential for highly-efficient and stable inverted planar PSCs.

Facile fabrication of a positively charged nanofiltration membrane for heavy metal and dye removal

• A simple fabrication procedure is used to fabricate a positively charged membrane. • The cross-linking reaction is performed in a mild condition at ambient temperature. • The membrane has a high water permeance and a high rejection for heavy metal salts. Positively charged membranes are essential for the removal of heavy metals from wastewater by nanofiltration (NF). A simple fabrication procedure for synthesizing a positively charged membrane with high permeance and high selectivity is needed to make this realistic. This work prepared a positively charged P84 NF membrane by chemical cross-linking of the asymmetric plain P84 membrane using hyperbranched polyethyleneimine (PEI). Instead of using organic solvent and thermal annealing, the cross-linking reaction occurred in mild conditions with a cross-linker concentration of 15 g L -1 and a cross-linking time of 20 h at ambient temperature in water. The modified membrane had increased surface hydrophilicity, surface roughness, and a positively charged surface. The resulting membrane had an excellent water flux of 43.2 L m -2 h −1 at 4 bar. The cross-linked P84 NF membrane showed high rejections of divalent heavy metals PbCl 2 , Ni(NO 3 ) 2 , ZnCl 2 , Cu(NO 3 ) 2 with rejections of 99.0%, 96.7%, 96.2%, 99.8%, respectively, which outperforms the commercial NF270 membrane tested in the same conditions. Due to the high cross-linking of the active surface layer, the membrane was found to reject positively charged organic dyes almost completely: Victory blue B (VBB, 506.08 g mo1 -1 ), methylene blue (MB, 319.85 g mo1 -1 ), and negatively charged Congo red (CR, 696.66 g mo1 -1 ). The convenient fabrication process could accelerate the progress of the positively charged NF membranes in potential applications of removing heavy metals and positively charged dyes from effluents in industries.

A detailed investigation of the core@shell structure of exchanged coupled magnetic nanoparticles after performing solvent annealing

Solvent annealing at around 300 °C resulted in a significant modification of the structure and the magnetic properties of core–shell metal oxide nanoparticles as shown by DANES and XMCD.

Enhancement of the performance of planar perovskite solar cells by active-layer surface/interface modification with optimal mixed solvent-antisolvent post-treatment

Modification of perovskite films surface/interface through the solvent vapor post-treatment during the film annealing can significantly improve the morphology and crystallinity of the perovskite film, thus enhances the efficiency of the perovskite solar cells (PSCs). In this work, we used a solvent-antisolvent mixture of Dimethyl sulfoxide (DMSO) and chlorobenzene (CB) in the post-treatment of perovskite films during device fabrication to achieve a high-power conversion efficiency of 19.15% in planar perovskite solar cells. The use of chlorobenzene as an additive to DMSO in the post-treatment of the perovskite films was shown to optimize the its morphology and resulted in films with highly fused grains. The modified perovskite film surface not only showed a decreased number of pin-hole and trap density at the surface, but also an increase in the charge transfer at the interfaces and reduced the susceptibility to low-frequency interface polarization. Furthermore, the impedance spectroscopy and I–V characteristics of the electron-only PSC devices also verified the conclusions above. Overall, this work demonstrates mixed solvent-antisolvent post-treatments of perovskite films as an effective modification strategy to tune their surface/interface properties. This approach is anticipated to be extrapolated to other categories of polycrystalline bulk materials and devices. Applying an optimized Post-treatment to the perovskite films (in perovskite photovoltaics) through mixed solvent annealing - DMSO:CB 1:2 (v/v), modifies its’ bulk/interface properties to be more favorable for photovoltaic devices, leading to a 17.97% increase in power conversion efficiency in planar perovskite solar cells compared to control devices. • A new strategy for modifying the perovskite films surface/interface morphology and crystallinity to achieve the higher device performance through the mixed solvent-antisolvent (DMSO:CB) post treatment has been studied. • The addition of chlorobenzene in the treatment of the perovskite films has been found to achieve larger yet highly fused grains and a suppressed ionic contribution to the perovskite solar cell operation. • The stabilized power conversion efficiency of the planar perovskite solar cells with the optimized treatment has increased by 17.85%.

Sub-25 nm Inorganic and Dielectric Nanopattern Arrays on Substrates: A Block Copolymer-Assisted Lithography.

A range of well-ordered inorganic (antimony, tin, and tungsten oxide) and dielectric (silica, alumina, and hafnia) nanoparticles and nanowire array patterns are created on substrates by a low-cost block copolymer (BCP) approach. A cylindrical-phase PS-b-PEO BCP is used as a template with hexagonally ordered perpendicular or parallel orientation of PEO cylinders. The solvent annealing parameters such as solvents, temperature, time, and so forth are optimized to achieve the desired patterns. An established BCP in situ inclusion protocol is utilized to achieve the material nanopatterns by spin coating the respective precursor ethanolic solution on the template followed by UV/ozone treatment for oxide conversion and polymer removal. Furthermore, the precursor solution concentrations and stirring times are calibrated to achieve isolated, well-ordered, and uniform-diameter and -thickness nanoparticles and nanowires. All of the material nanopatterns are mimicking the parent BCP nanopatterns. The phases of all of the nanopatterns are determined by X-ray photoelectron spectroscopy. The inorganic and dielectric nanopattern arrays are patterned on a graphoepitaxial substrate for device application.

Manipulation of Organic Afterglow by Thermodynamic and Kinetic Control.

The fabrication of room-temperature organic phosphorescence and afterglow materials, as well as the transformation of their photophysical properties, has emerged as an important topic in the research field of luminescent materials. Here, we report the establishment of energy landscapes in dopant-matrix organic afterglow systems where the aggregation states of luminescent dopants can be controlled by doping concentrations in the matrices and the methods of preparing the materials. Through manipulation by thermodynamic and kinetic control, dopant-matrix afterglow materials with different aggregation states and diverse afterglow properties can be obtained. The conversion from metastable aggregation state to thermodynamic stable aggregation state of the dopant-matrix afterglow materials to leads to the emergence of intriguing afterglow transformation behavior triggered by thermal and solvent annealing. The thermodynamically unfavorable reversible afterglow transformation process can also be achieved by coupling the dopant-matrix afterglow system to mechanical forces.

Molten-Salt-Assisted CsPbI3 Perovskite Crystallization for Nearly 20%-Efficiency Solar Cells.

Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (Voc ) as high as 1.2V, among the highest for this type of solar cell, thanks to its effectively reduced Voc deficit.

Sandwich Evaporation-Solvent Annealing Fabrication of Highly Crystalline MAPbIxCl3-x Perovskite Solar Cells.

Perovskites doped with chlorine (Cl-), which are usually fabricated using the solution process, can effectively improve the stability and carrier mobility. Compared with the low tolerance of the solution process that relies mostly on personal skill, thermal evaporation is an important method for large-scale production of perovskite solar cells but the production cost is high. In this study, the sandwich evaporation-solvent annealing (SE-SA) method is proposed. Using sandwich evaporation with a low-cost chamber of the sandwich evaporation technique (SET) made in the laboratory and with the help of DMSO steam-assisted crystallization, we have successfully produced chlorine-containing perovskite solar cells with a high crystallinity and a high efficiency of 15.1% with Voc = 0.98 V, Jsc = 21.94 mA/cm2, FF = 74.29%, and Rs = 3.66 Ω·cm2, which can greatly reduce the production cost. It is worth mentioning that all the processes are carried out outside a glove box, which makes it possible for large-scale production of chlorine-containing perovskite solar cells by evaporation.

Piezoionic sensors based on formulated PEDOT:PSS and Aquivion® for ionic polymer–polymer composites

In this work, an ionic polymer–polymer composites (IP2Cs) was developed as piezoionic sensors based on Aquivion® perfluorinated conducting membranes and modified PEDOT:PSS electrodes. The influence of solvent annealing, additive concentration and its nature (ionic liquid (IL), Aquivion®,…) on the electronic conductivity and the mechanical properties of modified PEDOT:PSS electrodes is investigated. The design of flexible free-standing PEDOT:PSS electrodes provides a new way of IP2Cs conception. Tri-layers are elaborated either by drop-casting or by thermocompressing of electrodes on top of commercial Aquivion® membranes swelled by an IL 1-ethyl-3-methylimidazolium bis (trifluoromethyl-sulfonyl) imide. The open-circuit voltage output is measured during bending stimulation experiments as function of the mechanical perturbation amplitude. These IP2Cs made from Aquivion® behaves as soft mechanical strain sensors with large electrical output signal as high as ΔE = 2.9 mV (Δϵ = ±2%) under optimal conditions. The influence of the IP2C’s manufacturing process, grade of Aquivion® membrane, and electrode’s properties is investigated. This study emphasized the significant contribution of the electrode’s mechanical properties that appears as a critical parameter for the development of high performance piezoionic sensors. In the near future, we will explore the opportunity to employ these Aquivion®-based IP2Cs as soft strain sensors for robotic and medical applications.

Hierarchical Microphase Behaviors of Chiral Block Copolymers under Kinetic and Thermodynamic Control

Hierarchical Microphase Behaviors of Chiral Block Copolymers under Kinetic and Thermodynamic Control

Investigation of Microstructures and Air Permeability of Aerogel-Coated Textile Fabric Materials

Abstract This study focuses on fabrication of aerogel-coated macroporous polyester fabrics for the purposes of filtration of nanometric airborne particles and potential application in facemasks. Syndiotactic polystyrene (sPS) and polyimide (PI) gels that provide respectively majority macropores (diameter > 50 nm) and mesopores (diameter 2 to 50 nm) are coated onto woven polyester fabrics via a dip coating process. The resultant materials are supercritically dried to obtain aerogelcoated fabrics. The results show that sPS is more suitable for the dip coating process. However, evaporation of the solvent during handling of gel-coated fabrics leads to closure of the surface pores that are later recovered via solvent annealing. The resultant aerogel-coated fabrics offer high air permeability (∼10–10 m2) and high filtration efficiency (> 99.95%) of airborne sodium chloride test particles of size 25 to 150 nm.

Fabrication of Nanoscale Oxide Textured Surfaces on Polymers.

Nanoscale textured surfaces play an important role in creating antibacterial surfaces, broadband anti-reflective properties, and super-hydrophobicity in many technological systems. Creating nanoscale oxide textures on polymer substrates for applications such as ophthalmic lenses and flexible electronics imposes additional challenges over conventional nanofabrication processes since polymer substrates are typically temperature-sensitive and chemically reactive. In this study, we investigated and developed nanofabrication methodologies to create highly ordered oxide nanostructures on top of polymer substrates without any lithography process. We developed suitable block copolymer self-assembly, sequential infiltration synthesis (SIS), and reactive ion etching (RIE) for processes on polymer substrates. Importantly, to prevent damage to the temperature-sensitive polymer and polymer/oxide interface, we developed the process to be entirely performed at low temperatures, that is, below 80 °C, using a combination of UV crosslinking, solvent annealing, and modified SIS and RIE processes. In addition, we developed a substrate passivation process to overcome reactivity between the polymer substrate and the SIS precursors as well as a high precision RIE process to enable deep etching into the thermally insulated substrate. These methodologies widen the possibilities of nanofabrication on polymers.