Waveguiding Microactuators Based on a Photothermally Responsive Nanocomposite Hydrogel

The incorporation of gold nanoparticles within thermally responsive poly(N‐isopropyl acrylamide) hydrogels provides a simple means to define photothermally addressable materials. Relying on such composite gels, it is established here that micropatterned bilayer photoactuators demonstrate rapid and highly reversible bending and unbending behavior in response to illumination with visible light. In addition to actuation by free space light, as in most previous research on such responsive nanocomposite hydrogels, light from a 532 nm laser is also waveguided through a plastic optical fiber directly into the photoactuator, providing remotely controllable actuators that do not require line‐of‐sight access.     

Programmed Deformations of 3D‐Printed Tough Physical Hydrogels with High Response Speed and Large Output Force

Shape‐morphing hydrogels have emerging applications in biomedical devices, soft robotics, and so on. However, successful applications require a combination of excellent mechanical properties and fast responding speed, which are usually a trade‐off in hydrogel‐based devices. Here, a facile approach to fabricate 3D gel constructs by extrusion‐based printing of tough physical hydrogels, which show programmable deformations with high response speed and large output force, is described. Highly viscoelastic poly(acrylic acid‐co‐acrylamide) (P(AAc‐co‐AAm)) and poly(acrylic acid‐co‐N‐isopropyl acrylamide) (P(AAc‐co‐NIPAm)) solutions or their mixtures are printed into 3D constructs by using multiple nozzles, which are then transferred into FeCl₃ solution to gel the structures by forming robust carboxyl–Fe³⁺ coordination complexes. The printed gel fibers containing poly(N‐isopropyl acrylamide) segment exhibit considerable volume contraction in concentrated saline solution, whereas the P(AAc‐co‐AAm) ones do not contract. The mismatch in responsiveness of the gel fibers affords the integrated 3D gel constructs the shape‐morphing ability. Because of the small diameter of gel fibers, the printed gel structures deform and recover with a fast speed. A four‐armed gripper is designed to clamp plastic balls with considerable holding force, as large as 115 times the weight of the gripper. This strategy should be applicable to other tough hydrogels and broaden their applications.     

Super Bulk and Interfacial Toughness of Physically Crosslinked Double‐Network Hydrogels

Conventional design wisdom prevents both bulk and interfacial toughness to be presented in the same hydrogel, because the bulk properties of hydrogels are usually different from the interfacial properties of the same hydrogels on solid surfaces. Here, a fully‐physically‐linked agar (the first network)/poly(N ‐hydroxyethyl acrylamide) (pHEAA, the second network), where both networks are physically crosslinked via hydrogen bonds, is designed and synthesized. Bulk agar/pHEAA hydrogels exhibit high mechanical properties (2.6 MPa tensile stress, 8.0 tensile strain, 8000 J m^?2 tearing energy, 1.62 MJ m^?3 energy dissipation), high self‐recovery without any external stimuli (62%/30% toughness/stiffness recovery), and self‐healing property. More impressively, without any surface modification, agar/pHEAA hydrogels can be easily and physically anchored onto different nonporous solid substrates of glass, titanium, aluminum, and ceramics to produce superadhesive hydrogel–solid interfaces (i.e., high interfacial toughness of 2000–7000 J m^?2). Comparison of as‐prepared and swollen gels in water and hydrogen‐bond‐breaking solvents reveals that strong bulk toughness provides a structural basis for strong interfacial toughness, and both high toughness mainly stem from cooperative hydrogen bonds between and within two networks and between two networks and solid substrates. This work demonstrates a new gel system to achieve superhigh bulk and interfacial toughness on nonporous solid surfaces.     

Highly Fluorescent Thienoviologen‐Based Polymer Gels for Single Layer Electrofluorochromic Devices

A highly fluorescent electrofluorochromic gel with quantum yields as high as 67% is prepared by incorporating the thienoviologen fluorophore 4,4′‐(2,2′‐bithiophene‐5,5′‐diyl)bis(1‐nonylpridinium)bistriflimide into a polymeric matrix. The fluorescent emission spectrum of the gel at low percentages of thienoviologen shows a strong band at 530 nm. A new intense fluorescence band at 630 nm can be induced by fluorophore aggregation. Single layer electrofluorochromic devices were readily prepared by sandwiching the polymer gels between two indium tin oxide (ITO) electrodes. The fluorescence intensity can be easily modulated between a fluorescent and a quenched state, in a wide visible spectral range, by direct electrochemical reduction of the thienoviologen fluorophore. It exhibits three reduction states, each with different emission properties. The reversible interconversion among these states leads to a high electrofluorochromic stability of the device, exhibiting switching times of a few seconds and, to the best of our knowledge, the highest contrast ratio (337).     

Reversible Electrochemically Triggered Delamination Blistering of Hydrogel Films on Micropatterned Electrodes

Stimuli responsive elastic instabilities provide opportunities for controlling the structures and properties of polymer surfaces, offering a range of potential applications. Here, a surface actuator based on a temperature and electrically responsive poly(N‐isopropyl acrylamide‐co‐sodium acrylate) hydrogel that undergoes a two‐step delamination and buckling instability triggered using micropatterned electrodes is described. The electrically actuated structures entail large out‐of‐plane displacements that take place on time‐scales of less than 1 s, in response to modest triggering voltages (?3–6 V). Alongside these experimental observations, finite element simulations are conducted to better understand the two‐step nature of the instability. In the first step, hydrogel films undergo delamination and formation of blisters, facilitated by electrochemical reduction of the thiol groups anchoring the film to the electrodes. Subsequently, at larger reducing potentials, the electrolytic current is sufficient to nucleate a gas bubble between the electrode and the gel, causing the delaminated region to adopt a straight‐sided blister shape. Finally, thermally induced deswelling of the gel allows the film to be returned to its flat state and readhered to the electrode, thereby allowing for repeated actuation.     

An Injectable Supramolecular Polymer Nanocomposite Hydrogel for Prevention of Breast Cancer Recurrence with Theranostic and Mammoplastic Functions

The high locoregional breast cancer recurrence rate poses a significant risk for patients' survival. Injecting theranostic drugs‐laden soft tissue‐like hydrogels into the resected breast cavity is a promising strategy to achieve both precisely local therapy of breast cancer and reconstructive mammoplasty. In this work, a robust injectable thermoresponsive supramolecular poly(N‐acryloyl glycinamide‐co‐acrylamide) (PNAm) hydrogel bearing polydopamine (PDA) coated‐gold nanoparticles (AuNPs) and doxorubicin (DOX) is fabricated. The supramolecular polymer nanocomposite (SPN) hydrogels exhibit an excellent photothermal effect arising from PDA‐AuNPs that are tightly fixed to the hydrogel matrix via PDA and amide moieties in the network, built‐in near infrared (NIR) light‐triggered gel–sol transition as well as tunable drug delivery. The PNAm‐PDAAu‐DOX sol driven by prior heating is injected into the cavity of resected cancerous breasts of rats where gelation occurred rapidly while the temperature decreased to body temperature, thereby finely serving as a breast filler. During 4 week of implantation, interval NIR light irradiation can mediate photothermal effect and concertedly controllable DOX release, thus collectively preventing the recurrence of breast cancer. Remarkably, this stable remoldable SPN hydrogel facilitates the breast reconstruction and can be tracked by computed tomography (CT) imaging owing to the intrinsic X‐ray attenuation property of the loaded AuNPs.     

Direct 3D Printing of High Strength Biohybrid Gradient Hydrogel Scaffolds for Efficient Repair of Osteochondral Defect

The emerging 3D printing technique allows for tailoring hydrogel‐based soft structure tissue scaffolds for individualized therapy of osteochondral defects. However, the weak mechanical strength and uncontrollable swelling intrinsic to conventional hydrogels restrain their use as bioinks. Here, a high‐strength thermoresponsive supramolecular copolymer hydrogel is synthesized by one‐step copolymerization of dual hydrogen bonding monomers, N‐acryloyl glycinamide, and N‐[tris(hydroxymethyl)methyl] acrylamide. The obtained copolymer hydrogels demonstrate excellent mechanical properties—robust tensile strength (up to 0.41 MPa), large stretchability (up to 860%), and high compressive strength (up to 8.4 MPa). The rapid thermoreversible gel ? sol transition behavior makes this copolymer hydrogel suitable for direct 3D printing. Successful preparation of 3D‐printed biohybrid gradient hydrogel scaffolds is demonstrated with controllable 3D architecture, owing to shear thinning property which allows continuous extrusion through a needle and also immediate gelation of fluid upon deposition on the cooled substrate. Furthermore, this biohybrid gradient hydrogel scaffold printed with transforming growth factor beta 1 and β‐tricalciumphosphate on distinct layers facilitates the attachment, spreading, and chondrogenic and osteogenic differentiation of human bone marrow stem cells (hBMSCs) in vitro. The in vivo experiments reveal that the 3D‐printed biohybrid gradient hydrogel scaffolds significantly accelerate simultaneous regeneration of cartilage and subchondral bone in a rat model.     

Dipole–Dipole and H‐Bonding Interactions Significantly Enhance the Multifaceted Mechanical Properties of Thermoresponsive Shape Memory Hydrogels

High strength hydrogels were previously constructed based on dipole–dipole and hydrogen bonding reinforcement. In spite of the high tensile and compressive strengths achieved, the fracture energy of the hydrogels strengthened with sole noncovalent bondings was rather low due to the lack in energy dissipating mechanism. In this study, combined dipole–dipole and hydrogen bonding interactions reinforced (DHIR) hydrogels are synthesized by one‐step copolymerization of three feature monomers, namely acrylonitrile (AN, dipole monomer), acrylamide (AAm, H‐bonding monomer), and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS, anionic monomer) in the presence of PEGDA575, a hydrophilic crosslinker. The electrostatic repulsion from PAMPS allows the gel network to absorb water readily, and meanwhile the synergistic effect of dipole–dipole and H‐bonding interactions enable the DHIR hydrogel to withstand up to 8.3 MPa tensile stress, 4.8 MPa compressive stress and 140–716% elongation at break with the fracture energy reaching as high as 5500 J/m². In addition, this DHIR hydrogel exhibits reversible mechanical properties after undergoing cyclic loading and unloading. Interestingly, the DHIR hydrogels with appropriate compositions demonstrate temperature‐tunable mechanical properties as well as accompanied shape memory effect. The dual noncovalent bonding strengthening mechanism reported here offers a universal strategy for significantly enhancing the comprehensive mechanical properties of hydrogels.     

Biotissue-Inspired Anisotropic Carbon Fiber Composite Hydrogels for Logic Gates,Integrated Soft Actuators,and Sensors with Ultra-High Sensitivity

Natural biotissues like muscles, ligaments, and nerves have highly aligned structures, which play critical roles in directional signal transport, sensing, and actuation. Inspired by anisotropic biotissues, composite hydrogels with outstanding mechanical properties and conductivity are developed by compositing thermo-responsive poly (N-isopropylacrylamide) (PNIPAM) hydrogels with highly aligned carbon fibers (CFs). The anisotropic hydrogels show superior tensile strength (3.0 ± 0.3), modulus (74 ± 7.0 MPa), excellent electrical conductivity (≈670 S m⁻¹), and ultra-high sensitivity (gauge factor up to 647) along CFs, with an anisotropic ratio (AR) up to 740 over those in perpendicular direction. The extremely high AR in conductivity (more than 400) produces high-level output in parallel direction and low-level output in perpendicular direction with a direct current (DC) power supply, which is used to fabricate AND and OR gates. Moreover, the composite hydrogels are converted into thermo-responsive actuators with CFs twisted before compositing with PNIPAM/clay network. The pre-twisted CF helices impart internal stress that drives reversible actuation of hydrogel helices upon thermo-stimulating. The actuation is self-sensed due to the extremely high sensitivity of the composite hydrogels. Such biomimetic anisotropic self-sensing hydrogel actuators resemble natural biotissues with both actuation and sensing capabilities, and have promise applications for artificial robotics.     

Photopatterned Multidimensional Fluorescent Images

New methods that yield covert fluorescent images are of significant interest for applications in anti‐counterfeit technology. Printing methods that offer access to spatially controlled fluorescence intensity are needed in order to accurately reproduce unique and complex images. Herein, the use of photoreactive inks containing 9,9′‐bis(anthracene)sulfoxide (AnSO) to create complex images with spatially controlled fluorescence intensity is presented. Under UV irradiation, the SO‐bridge between anthracene units in AnSO is extruded to yield the highly luminescent molecule 9,9′‐bianthryl (BA) in quantitative yields. The irreversible formation of BA is leveraged to create multidimensional fluorescent security features that can be patterned using light and easily interpreted using the CCD camera of a mobile phone.     

Hybrid Shear-Thinning Hydrogel Integrating Hyaluronic Acid with ROS-Responsive Nanoparticles

Nanoparticle (NP) supra-assembly offers unique opportunities to tune macroscopic hydrogels’ mechanical strength, material degradation, and drug delivery properties. Here, synthetic, reactive oxygen species (ROS)-responsive NPs are physically cross-linked with hyaluronic acid (HA) through guest-host chemistry to create shear-thinning NP/HA hydrogels. A library of triblock copolymers composed of poly(propylene sulfide)-b-poly(N,N-dimethylacrylamide)-b-poly(N,N-dimethylacrylamide-co-N-(1-adamantyl)acrylamide) are synthesized with varied triblock architectures and adamantane grafting densities and then self-assembled into NPs displaying adamantane on their surface. Self-assembled NPs are mixed with β-cyclodextrin grafted HA to yield eighteen NP/HA hydrogel formulations. The NP/HA hydrogel platform demonstrates superior mechanical strength to HA-only hydrogels, susceptibility to oxidative/enzymatic degradation, and inherent cell-protective, antioxidant function. The performance of NP/HA hydrogels is shown to be affected by triblock architecture, guest/host grafting densities, and HA composition. In particular, the length of the hydrophilic second block and adamantane grafting density of self-assembled NPs significantly impacts hydrogel mechanical properties and shear-thinning behavior, while ROS-reactivity of poly(propylene sulfide) protects cells from cytotoxic ROS and reduces oxidative degradation of HA compared to HA-only hydrogels. This study provides insight into polymer structure-function considerations for designing hybrid NP/HA hydrogels and identifies antioxidant, shear-thinning hydrogels as promising injectable delivery platforms for small molecule drugs and therapeutic cells.     

Combining 3D Printing with Electrospinning for Rapid Response and Enhanced Designability of Hydrogel Actuators

Porous structures have emerged as a breakthrough of shape‐morphing hydrogels to achieve a rapid response. However, these porous actuators generally suffer from a lack of complexity and diversity in obtained 3D shapes. Herein, a simple yet versatile strategy is developed to generate shape‐morphing hydrogels with both fast deformation and enhanced designability in 3D shapes by combining two promising technologies: electrospinning and 3D printing. Elaborate patterns are printed on mesostructured stimuli‐responsive electrospun membranes, modulating in‐plane and interlayer internal stresses induced by swelling/shrinkage mismatch, and thus guiding morphing behaviors of electrospun membranes to adapt to changes of the environment. With this strategy, a series of fast deformed hydrogel actuators are constructed with various distinctive responsive behaviors, including reversible/irreversible formations of 3D structures, folding of 3D tubes, and formations of 3D structures with multi low‐energy states. It is worth noting that although poly(N‐isopropyl acrylamide) is chosen as the model system in the present research, our strategy is applicable to other stimuli‐responsive hydrogels, which enriches designs of rapid deformed hydrogel actuators.     

Hybrid Capsules via Self‐Assembly of Thermoresponsive and Interfacially Active Bionanoparticle–Polymer Conjugates

New bionanoparticles have been prepared from horse spleen ferritin by grafting thermoresponsive poly(N‐isopropyl acrylamide) (PNIPAAm) and photo‐crosslinkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide (DMIAAm) from the protein surface. The 72 addressable amino groups on the exterior of HSF were modified with N‐hydroxysuccinimide‐activated 2‐bromo‐isobutyrate to form a macro‐initiator for atom transfer radical polymerization, which was performed in water/DMF solutions at low temperature. The modification of the HSF and the presence of the polymer shell were confirmed by size exclusion chromatography (SEC), sodium dodecyl sulfate‐polyacrylamide gel‐electrophoresis, transmission electron microscopy, and scanning force microscopy. The thermoresponsive behavior of the ferritin‐PNIPAAm conjugates was investigated in solution by UV–vis spectroscopy showing a phase transition in the form of a cloud point around 32 °C. Further, dynamic light scattering revealed an increasing hydrodynamic radius around this transition, indicating aggregation of the particles at elevated temperatures which was confirmed by transmission electron microscopy. Initial experiments show that the particles are highly surface active, much more than the individual components alone, which was demonstrated by pendant‐drop interfacial tension measurements. This leads to the fact that they form stable Pickering emulsions, i.e., emulsion droplets decorated with polymer‐modified bionanoparticles which can be cross‐linked successively. This allows the formation of capsules with thermoresponsiveness for controlled release purposes, e.g., in drug delivery.     

Comparison of Charge‐Carrier Transport in Thin Films of Spiro‐Linked Compounds and Their Corresponding Parent Compounds

The charge‐transport properties of the spiro‐linked compounds 2,2′,7,7′‐tetrakis(diphenylamino)‐9,9′‐spirobifluorene, 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methylphenylamino)‐9,9′‐spirobifluorene, 2,2′,7,7′‐tetra(m‐tolyl‐phenylamino)‐9,9′‐spirobifluorene, and 2,2′,7,7′‐tetra(N‐phenyl‐1‐naphthylamine)‐9,9′‐spirobifluorene, and their corresponding parent compounds, N,N,N′,N′‐tetraphenylbenzidine, N,N,N′,N′‐tetrakis(4‐methylphenyl)benzidine, and N,N′‐bis(3‐methylphenyl)‐(1,1′‐biphenyl)‐4,4′‐diamine, N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)‐1,1′‐biphenyl‐4,4′‐diamine, are investigated. The field‐effect mobilities of charge carriers in thin films of the parent compounds are slightly higher than those of the spiro‐linked compounds. However, the transistor action of the parent‐compound thin films vanishes because the films crystallize after being stored in ambient atmosphere for a few days. In contrast, the hole mobilities in thin films of the spiro‐linked compounds do not change significantly after the samples are stored in ambient atmosphere for up to nine months. Also discussed is the temperature dependency of the mobilities of charge carriers, which is presented using two models, namely the Arrhenius and the Gaussian disorder models.     

Toward the New Generation of Surgical Meshes with 4D Response: Soft,Dynamic, and Adaptable

Herein, a facile approach toward transforming a 2D polypropylene flexible mesh material into a 4D dynamic system is presented. The versatile platform, composed by a substrate of knitted fibers of isotactic polypropylene (iPP) mesh and a coating of thermosensitive poly(N‐isopropylacrylamide‐co‐N,N’‐methylene bis(acrylamide) (PNIPAAm‐co‐MBA) hydrogel, covalently bonded to the mesh surface, after cold‐plasma surface treatment and radical polymerization, is intended to undergo variations in its geometry via its reversible folding/unfolding behavior. The study is the first to trace the 3D movement of a flat surgical mesh, intended to repair hernia defects, under temperature and humidity control. An infrared thermographic camera and an optical microscope are used to evaluate the macroscopic and microscopic structure stimulus response. The presence of the PP substrate and the distribution of the gel surrounding the PP threads, affect both the PNIPAAM gel expansion/contraction as well as the time of folding/unfolding response. Furthermore, PP‐g‐PNIPAAm meshes show an increase in the bursting strength of ≈16% with respect to the uncoated mesh, offering a strongest and adaptable system for its future implantation in human body. The findings reported offer unprecedented application possibilities in the biomedical field.     

Alginate‐Boronic Acid: pH‐Triggered Bioinspired Glue for Hydrogel Assembly

The development of bioadhesives has become an emerging research field for tissue sealants, wound dressings, and hemostatic agents. However, assembling hydrogels using bioadhesive‐mediated attachment remains a challenging task. Significantly high water content (>90%) in hydrogels compared to that of biological tissues is the main cause of failure. Considering that hydrogels are primary testing scaffolds mimicking in vivo environments, developing strategies to assemble hydrogels that exhibit diverse properties is important. Self‐healing gels have been reported, but such gels often lack biocompatibility, and two gel pieces should be identical in chemistry for assembly, thus not allowing co‐existence of diverse biological environments. Herein, a mussel‐mimetic cis‐diol‐based adhesive, alginate‐boronic acid, that exhibits pH‐responsive curing from a viscoelastic solution to soft gels is developed. Associated mechanisms are that 1) polymeric diffusion occurs at interfaces utilizing intrinsic high water content; 2) the conjugated cis‐diols strongly interact/entangle with hydrogel chains; 3) curing processes begin by a slight increase in pH, resulting in robust attachment of diverse types of hydrogel building blocks for assembly. The findings obtained with alginate‐boronic acid glues suggest a rational design principle to attach diverse hydrogel building blocks to provide platforms mimicking in vivo environments.     

Synergistic Computational‐Experimental Approach to Improve Ionene Polymer‐Based Functional Hydrogels

The manifold applications of ionene‐based materials such as hydrogels in daily life, biomedical sciences, and industrial processes are a consequence of their unique physical and chemical properties, which are governed by a judicious balance between multiple non‐covalent interactions. However, one of the most critical aspects identified for a broader use of different polyelectrolytes is the need of raising their gelation efficiency. This work focuses on surfactant‐free ionene polymers 1 ? 3 containing DABCO and N,N′‐(x‐phenylene)dibenzamide (x = ortho‐/meta‐/para‐) linkages as model systems to develop a combined computational‐experimental approach to improve the hydrogelation through a better understanding of the gelation mechanism. Molecular dynamics simulations of isomeric ionenes 1–3 with explicit water molecules point out remarkable differences in the assembly of the polymeric chains in each case. Interchain regions with high degree of hydration (i.e., polymer···water interactions) and zones dominated by polymer···polymer interactions are evident in the case of ortho‐ ( 1 ) and meta‐ ( 2 ) isomeric ionenes, whereas domains controlled by polymer···polymer interactions are practically inexistent in 3 . In excellent agreement, ortho‐ionene 1 provides experimentally the best hydrogels with unique features such as thixotropic behavior and dispersion ability for single‐walles carbon nanotubes.     

Highly Efficient Self‐Healable and Dual Responsive Cellulose‐Based Hydrogels for Controlled Release and 3D Cell Culture

To face the increasing demand of self‐healing hydrogels with biocompatibility and high performances, a new class of cellulose‐based self‐healing hydrogels are constructed through dynamic covalent acylhydrazone linkages. The carboxyethyl cellulose‐graft‐dithiodipropionate dihydrazide and dibenzaldehyde‐terminated poly(ethylene glycol) are synthesized, and then the hydrogels are formed from their mixed solutions under 4‐amino‐DL‐phenylalanine (4a‐Phe) catalysis. The chemical structure, as well as microscopic morphologies, gelation times, mechanical and self‐healing performances of the hydrogels are investigated with ¹H NMR, Fourier transform infrared spectroscopy, atomic force microscopy, rheological and compression measurements. Their gelation times can be controlled by varying the total polymer concentration or 4a‐Phe content. The resulted hydrogels exhibit excellent self‐healing ability with a high healing efficiency (≈96%) and good mechanical properties. Moreover, the hydrogels display pH/redox dual responsive sol‐gel transition behaviors, and are applied successfully to the controlled release of doxorubicin. Importantly, benefitting from the excellent biocompatibility and the reversibly cross‐linked networks, the hydrogels can function as suitable 3D culture scaffolds for L929 cells, leading to the encapsulated cells maintaining a high viability and proliferative capacity. Therefore, the cellulose‐based self‐healing hydrogels show potential applications in drug delivery and 3D cell culture for tissue engineering.     

A Thiophene‐Based Anchoring Ligand and Its Heteroleptic Ru(II)‐Complex for Efficient Thin‐Film Dye‐Sensitized Solar Cells

A novel heteroleptic Ru^II complex (BTC‐2) employing 5,5′‐(2,2′‐bipyridine‐4,4′‐diyl)‐bis(thiophene‐2‐carboxylic acid) (BTC) as the anchoring group and 4,4′‐ dinonyl‐2,2′‐bipiridyl and two thiocyanates as ligands is prepared. The photovoltaic performance and device stability achieved with this sensitizer are compared to those of the Z‐907 dye, which lacks the thiophene moieties. For thin mesoporous TiO₂ films, the devices with BTC‐2 achieve higher power conversion efficiencies than those of Z‐907 but with a double‐layer thicker film the device performance is similar. Using a volatile electrolyte and a double layer 7 + 5 μm mesoporous TiO₂ film, BTC‐2 achieves a solar‐to‐electricity conversion efficiency of 9.1% under standard global AM 1.5 sunlight. Using this sensitizer in combination with a low volatile electrolyte, a photovoltaic efficiency of 8.3% is obtained under standard global AM 1.5 sunlight. These devices show excellent stability when subjected to light soaking at 60 °C for 1000 h. Electrochemical impedance spectroscopy and transient photovoltage decay measurements are performed to help understand the changes in the photovoltaic parameters during the aging process. In solid state dye‐sensitized solar cells (DSSCs) using an organic hole‐transporting material (spiro‐MeOTAD, 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene), the BTC‐2 sensitizer exhibits an overall power conversion efficiency of 3.6% under AM 1.5 solar (100 mW cm^?2) irradiation.     

Origin of Enhanced Hole Injection in Inverted Organic Devices with Electron Accepting Interlayer

Conventional organic light emitting devices have a bottom buffer interlayer placed underneath the hole transporting layer (HTL) to improve hole injection from the indium tin oxide (ITO) electrode. In this work, a substantial enhancement in hole injection efficiency is demonstrated when an electron accepting interlayer is evaporated on top of the HTL in an inverted device along with a top hole injection anode compared with the conventional device with a bottom hole injection anode. Current–voltage and space‐charge‐limited dark injection (DI‐SCLC) measurements were used to characterize the conventional and inverted N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)(1,1′biphenyl)‐4,4′diamine (NPB) hole‐only devices with either molybdenum trioxide (MoO₃) or 1,4,5,8,9,11‐hexaazatriphenylene hexacarbonitrile (HAT‐CN) as the interlayer. Both normal and inverted devices with HAT‐CN showed significantly higher injection efficiencies compared to similar devices with MoO₃, with the inverted device with HAT‐CN as the interlayer showing a hole injection efficiency close to 100%. The results from doping NPB with MoO₃ or HAT‐CN confirmed that the injection efficiency enhancements in the inverted devices were due to the enhanced charge transfer at the electron acceptor/NPB interface.