Two‐photon Polymerization (2PP) process for high‐resolution 3D printing presents an opportunity to design micro‐scale structures with a high surface‐to‐volume ratio for highly responsive devices. However, these acrylate or thiol‐based resins are electrically insulating and non‐functional in nature, therefore limiting their widespread application in biosensing and biotechnology. Here, a novel conductive polymeric composite resin to print conductive 3D micro‐structures via the 2PP technique is developed and its application in sensing are demonstrated. The composite consists of acrylate‐based 2PP resin and Poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS), a conductive and biocompatible organic semiconductor The PEDOT:PSS incorporation in resin through Raman and X‐ray photoelectron spectroscopy (XPS) is studied. An electrical conductivity of 3.5 × 102 S cm−1 in a 20 µm long and 10 µm high 3D printed micro‐structure which is suitable for electronic applications is achieved. An ultra‐fast micro‐3D printed humidity sensor with a response and recovery time of 0.15 and 0.3 s respectively is demonstrated. The printed sensors show high sensitivity in humidity levels of 0–80%RH. As a proof of concept, the real‐time respiration of a human body is recorded, implying a potential application in health monitoring systems.

Replicating the tactile sensing mechanisms, conformity, and feel of real skin is essential for next- generation human-machine interfaces. However, producing tissue-like multilayered geometries and integrating them as e-skin systems requires simplifying and standardizing their manufacture. Here, we present a scalable and cost-effective cure-on-demand strategy for 3D printing nanocomposite silicone rubbers and integrating them into complex soft structures with 1200 % enhanced pressure-strain sensitivity. By utilizing a controlled in-situ mixing of catalyst-cured silicones and shear-driven alignment of carbon nanofibers (CNF), we construct percolated networks with conductivities up to 130 S m(-1) layer-by-layer. We investigate the influence of ink composition, printing parameters, geometrical design, and material density on the mechanical properties, stretchability, sensitivity, and antimicrobial activity of 3D printed piezoresistive sensors and build skin-like interfaces that detect minimal deformations like human physiological signs. This customizable, biocompatible, and robust e-skin holds promise for cost-effective integration in rehabilitation medicine, smart robotics applications, and extended reality (XR) interactive experiences.

Layered III-VI monochalcogenides such as gallium telluride (GaTe) and indium selenide (InSe) have positioned themselves for high-performance optoelectronics including radiation detectors and solar cells due to the optimum band gap as a solar window material and as semi-insulating at room temperature [1]. The unique crystal structure of GaTe induces interesting consequences on the band structure and hence the optical and electronic characteristics, such as direct band gap and strong excitonic absorption [2]. However, the fabrication of the photo detectors using these materials on flexible substrates employing printing technologies owing to the cost effective, fast, and easy production properties is of keen interest. In this work, we utilize screen printing and slide dye coating technologies to fabricate a photodetector based on solution-processed GaTe on PET sheets. To do this, PET substrate is respectively cleaned in acetone, iso-propanol, and distilled water by using ultrasonic sonicator and dried using $\mathrm{N}_{2}$ . After that, silver (Ag) nanoparticle-based ink is used to screen-print the interdigit for top contacts as shown in Fig. 1(a). Then, for sintering a heating oven is used at 120°C for 10 min. In order to change hydrophobicity, surface treatment is done using ozone plasma for 5 min. Also, GaTe ink is prepared using liquid phase exfoliation (LPE) method [2]. To do this, 10 mg of GaTe is immersed into iso-propanol and sonicated for 45 min. utilizing ultrasound sonicator followed by slide dye coating to print GaTe layer with 60 passes, see Fig. 1(b).

Solution-processed metal halide perovskite (MHP) single crystals (SCs) are in high demand for a growing number of printed electronic applications due to their superior optoelectronic properties compared to polycrystalline thin films. There is an urgent need to make SC fabrication facile, scalable, and compatible with the printed electronic manufacturing infrastructure. Here, a universal cosolvent evaporation (CSE) strategy is presented by which perovskite SCs and arrays are produced directly on substrates via printing and coating methods within minutes at room temperature from drying droplets. The CSE strategy successfully guides the supersaturation via controlled drying of droplets to suppress all crystallization pathways but one, and is shown to produce SCs of a wide variety of 3D, 2D, and mixed-cation/halide perovskites with consistency. This approach works with commonly used precursors and solvents, making it universal. Importantly, the SC consumes the precursor in the droplet, which enables the large-scale fabrication of SC arrays with minimal residue. Direct on-chip fabrication of 3D and 2D perovskite photodetector devices with outstanding performance is demonstrated. The approach shows that any MHP SC can now be manufactured on substrates using precision printing and scalable, high-throughput coating methods.

Accelerating the shift towards renewable materials and sustainable processes for printed organic electronic devices is crucial for a green circular economy. Currently, the fabrication of organic devices with competitive performances is linked to toxic petrochemical-based solvents with considerable carbon emissions. Here we show that terpene solvents obtained from renewable feedstocks can replace non-renewable environmentally hazardous solvent counterparts in the production of highly efficient organic photovoltaics (OPVs) light-emitting diodes (OLEDs) and field-effect transistors (OFETs) with on-par performances. Using a Hansen solubility ink formulation framework, we identify various terpene solvent systems and investigate effective film formation and drying mechanisms required for optimal charge transport. This approach is universal for state-of-the-art materials in OPVs, OLEDs and OFETs. We created an interactive library for green solvent selections and made it publicly available through the OMEGALab website. As potential carbon-negative solvents, terpenes open a unique and universal approach towards efficient, large-area and stable organic electronic devices.

Slot-die (SD) coating is used to fabricate fully solution processed organic solar cells (OSCs) based on a blend of high performance donor polymer (PTB7-Th) and a non-fullerene acceptor (IEICO-4F) for stable devices over extended periods of operation. The optimization of a sequential deposition process of transport and active layers, under ambient conditions, enable high efficiency slot-die coated solar cells with remarkable power conversion efficiencies (PCE) > 11.0% to bridge the gap between lab-to-fab. Fully slot-die coated inverted OSCs are demonstrated with efficiencies reaching 11% along with 1 cm(2) devices, proving the scalability and reproducibility of the proposed technique. Further, replacing the evaporated Ag electrode with solution processed Ag nanowire (AgNW) electrodes shows the highest light utilization efficiency of 5.26% for semi-transparent OSC with a PCE of 9.07% and average visible transmission of 58%.

The choice of interfacial materials and their properties play a critical role in determining solar cell performance and stability. For compatibility with roll-to-roll printing, it is desirable to develop stable cathode interface layers (CILs) that can be processed over the photoactive layer using orthogonal solvents. In this study, an n-type naphthalene diimide core and oligo (ethylene glycol) side-chain-based conjugated polymer is reported as a universal, efficient CIL for organic and perovskite photovoltaics. Besides good thermal stability and easy processing in alcohol/water, the new CIL is found to possess electron transport properties with an electrical conductivity of 2.3 x 10(-6) S cm(-1), enabling its use as a CIL with a film thickness of up to similar to 35(+/- 2) nm. Utilizing the new CIL, 16% power conversion efficiency (PCE) is achieved for organic solar cells (OSCs) based on the PM6-Y6 photoactive layer (8.9% PCE for no CIL and 15.1% with state-of-the-art CIL, PDINO), and perovskite solar cells from methylammonium lead iodide yielded a PCE of 17.6%. Compared to the reference devices, the new CIL reduced trap-assisted carrier recombination and increased the built-in potential by 80 mV, simultaneously enhancing all photovoltaic parameters. Moreover, new CIL based devices had better photostability with no burn-in losses.

New polymer donors and nonfullerene acceptors have elevated the performance and stability of solar cells to higher grounds. To achieve their full potential, they require their adaptation to scalable and cost‐effective solution manufacturing techniques for large area deposition. Likewise, formulating scalable solution‐based transport layer inks that are compatible with the photoactive layer is imperative. This manuscript reports the full integration of solution‐based transport layers and electrode alongside a PTB7‐Th:IEICO‐4F bulk heterojunction in inverted architecture through inkjet‐printing, resulting in power conversion efficiencies up to 12.4% opaque devices and 9.5% semitransparent devices with average visible transmittance values of 50.1%, including hole transport layer. The wetting envelope of the highly‐hydrophobic photoactive layer alongside the surface energy of candidate solutions and solvents allows the formulation of thick transport layer inks that are compatible with the drop‐on‐demand inkjet‐printing process and yield uniform and homogenous films. Moreover, the surface energy components of the donor and acceptor serves as a fingerprint to assess the vertical stratification of the photoactive layer with the inclusion of different solvents. This methodology addresses a scale‐up bottleneck of solution‐based transport layers for high‐efficiency organic cells, enabling its adaptation to high‐throughput techniques including slot‐die and roll‐to‐roll coating.

Ultra‐lightweight solar cells have attracted enormous attention due to their ultra‐conformability, flexibility, and compatibility with applications including electronic skin or miniaturized electronics for biological applications. With the latest advancements in printing technologies, printing ultrathin electronics is becoming now a reality. This work offers an easy path to fabricate indium tin oxide (ITO)‐free ultra‐lightweight organic solar cells through inkjet‐printing while preserving high efficiencies. A method consisting of the modification of a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink with a methoxysilane‐based cross‐linker (3‐glycidyloxypropyl)trimethoxysilane (GOPS)) is presented to chemically modify the structure of the electrode layer. Combined with plasma and solvent post‐treatments, this approach prevents shunts and ensures precise patterning of solar cells. By using poly(3‐hexylthiophene) along rhodanine‐benzothiadiazole‐coupled indacenodithiophene (P3HT:O‐IDTBR), the power conversion efficiency (PCE) of the fully printed solar cells is boosted up to 4.73% and fill factors approaching 65%. All inkjet‐printed ultrathin solar cells on a 1.7 µm thick biocompatible parylene substrate are fabricated with PCE reaching up to 3.6% and high power‐per‐weight values of 6.3 W g −1 . After encapsulation, the cells retain their performance after being exposed for 6 h to aqueous environments such as water, seawater, or phosphate buffered saline, paving the way for their integration in more complex circuits for biological systems.

SPECIALTY GRAND CHALLENGE article Front.Electron., 30 September 2020Sec. Flexible Electronics Volume 1 - 2020 | https://doi.org/10.3389/felec.2020.594003

Novel emerging materials for organic solar cells, such as nonfullerene acceptors, are paving the way for commercialization of organic photovoltaics. Their utilization in unconventional applications, such as conformable and disposable electronics, has turned the focus to inkjet printing as a fabrication method with advantages including low material usage, rapid digital design changes, and high resolution. In this work, the fabrication of efficient nonfullerene acceptor devices through inkjet printing for organic photovoltaic applications is reported for the first time. The engineering of printable poly‐3‐hexylthiophene:rhodanine‐benzothiadiazole‐coupled indacenodithiophene (P3HT:O‐IDTBR) inks is centered on tuning the rheological properties for proper droplet ejection and the selection of solvents, including hydrocarbons, that meet solubility and volatility requirements to avoid common inkjet printing complications like nozzle clogging. The optimization of printing parameters including drop spacing and deposition temperatures results in homogeneous P3HT:O‐IDTBR films with device efficiencies of up to 6.47% for small lab‐scale devices (0.1 cm 2 ), comparable with that of spin‐coating or blade‐coating. A 2 cm 2 inkjet‐printed device is also shown to achieve a remarkable efficiency of 6%. To demonstrate their potential usage in customized applications, large‐area devices are fabricated in the shape of a marine turtle with 4.76% efficiency, showcasing the versatility of the inkjet‐printing process for efficient organic photovoltaics.

With the advent of flexible and wearable electronics and sensors, there is an urgent need to develop energy-harvesting solutions that are compatible with such wearables. However, many of the proposed energy-harvesting solutions lack the necessary mechanical properties, which make them susceptible to damage by repetitive and continuous mechanical stresses, leading to serious degradation in device performance. Developing new energy materials that possess high deformability and self-healability is essential to realize self-powered devices. Herein, a thermoelectric ternary composite is demonstrated that possesses both self-healing and stretchable properties produced via 3D-printing method. The ternary composite films provide stable thermoelectric performance during viscoelastic deformation, up to 35% tensile strain. Importantly, after being completely severed by cutting, the composite films autonomously recover their thermoelectric properties with a rapid response time of around one second. Using this self-healable and solution-processable composite, 3D-printed thermoelectric generators are fabricated, which retain above 85% of their initial power output, even after repetitive cutting and self-healing. This approach represents a significant step in achieving damage-free and truly wearable 3D-printed organic thermoelectrics.

The fields of photovoltaics, photodetection and light emission have seen tremendous activity in recent years with the advent of hybrid organic-inorganic perovskites. Yet, there have been far fewer reports of perovskite-based field-effect transistors. The lateral and interfacial transport requirements of transistors make them particularly vulnerable to surface contamination and defects rife in polycrystalline films and bulk single crystals. Here, we demonstrate a spatially-confined inverse temperature crystallization strategy which synthesizes micrometre-thin single crystals of methylammonium lead halide perovskites MAPbX(3) (X = Cl, Br, I) with sub-nanometer surface roughness and very low surface contamination. These benefit the integration of MAPbX3 crystals into ambipolar transistors and yield record, room-temperature field-effect mobility up to 4.7 and 1.5 cm(2) V-1 s(-1) in p and n channel devices respectively, with 10(4) to 10(5) on-off ratio and low turn-on voltages. This work paves the way for integrating hybrid perovskite crystals into printed, flexible and transparent electronics.