Hybrid perovskites show enormous potential for display due to their tunable emission, high color purity, strong photoluminescence and electroluminescence. For display applications, full-color and high-resolution patterning is compulsory, however, current perovskite processing such as spincoating fails to meet these requirements. Here, electrohydrodynamic (EHD) printing, with the unique advantages of high-resolution patterning and large scalability, is introduced to fabricate full-color perovskite patterns. Perovskite inks via simple precursor mixing are prepared to in situ crystallize tunableand bright-photoluminescence perovskite arrays without adding antisolvent. Through optimizing the EHD printing process, a high-resolution dot matrix of 5 µm is achieved. The as-printed patterns and pictures show full color and high controllability in micrometer dimension, indicating that the EHD printing is a competitive technique for future halide perovskite-based high-quality display.

Piezoelectric structures, in forms that allow mere in-surface deformations under large strains, are attractive for bio-integrated systems. Here, mechano-electrospinning (MES) is presented to direct-write straight nanofibers of polyvinylidene fluoride onto a prestrained poly(dimethylsiloxane) (PDMS) substrate, to position and polarize a piezoelectric nanofiber array in one-step. Wrinkled/non-wrinkled buckling modes are found when the substrates are released, and the morphology of the direct-written fiber proved the key to determine the buckling modes, which can be tuned precisely by MES parameters. The non-wrinkled, stretchable piezoelectric devices with a highly synchronized serpentine fiber array exhibit their in-surface deformation and stable piezoelectric performance up the failure strain of PDMS (∼110% in our study), which may be used as stretchable sensors and energy converters/providers.

Nanofibers/nanowires usually exhibit exceptionally low flexural rigidities and remarkable tolerance against mechanical bending, showing superior advantages in flexible electronics applications. Electrospinning is regarded as a powerful process for this 1D nanostructure; however, it can only be able to produce chaotic fibers that are incompatible with the well-patterned microstructures in flexible electronics. Electro-hydrodynamic (EHD) direct-writing technology enables large-scale deposition of highly aligned nanofibers in an additive, noncontact, real-time adjustment, and individual control manner on rigid or flexible, planar or curved substrates, making it rather attractive in the fabrication of flexible electronics. In this Review, the ground-breaking research progress in the field of EHD direct-writing technology is summarized, including a brief chronology of EHD direct-writing techniques, basic principles and alignment strategies, and applications in flexible electronics. Finally, future prospects are suggested to advance flexible electronics based on orderly arranged EHD direct-written fibers. This technology overcomes the limitations of the resolution of fabrication and viscosity of ink of conventional inkjet printing, and represents major advances in manufacturing of flexible electronics.

Direct full‐color image photodetectors without dichroic prisms or sophisticated color filters have considerable advantages in target recognition and information acquisition for electronic eyes and wearable sensors. However, the ability to combine various multispectral semiconductors in a high‐resolution and cost‐effective manner is still challenging. Here, high‐resolution electrohydrodynamic (EHD) printing, together with ionic liquid methylammonium acetate (MAAc) as the solvent, is first introduced to directly integrate various spectral‐response perovskite films into a pixelized full‐color photodetector. EHD printing enables micro/nanopatterning by using high electrical force to induce jetting, and MAAc improves film quality with scant pinholes and large‐size grains by decreasing the perovskite growth rate. By optimizing the printing process and crystallization condition, 1 µm perovskite dot arrays are EHD printed; this is, to the best of knowledge, the smallest printed feature size of perovskite application. And the photodetector still achieves high R and D* values of 14.97 A W‐1 and 1.41 × 1012 Jones, respectively. Finally, an integrated flexible full‐color image photodetector is constructed, which successfully realizes light signal detection and color recognition, paving a versatile and competitive approach for future full‐color image sensors and artificial vision systems.

Over the last decade, extensive efforts have been made on utilizing advanced materials and structures to improve the properties and functionalities of flexible electronics. While the conventional ways are approaching their natural limits, a revolutionary strategy, namely metamaterials, is emerging toward engineering structural materials to break the existing fetters. Metamaterials exhibit supernatural physical behaviors, in aspects of mechanical, optical, thermal, acoustic, and electronic properties that are inaccessible in natural materials, such as tunable stiffness or Poisson's ratio, manipulating electromagnetic or elastic waves, and topological and programmable morphability. These salient merits motivate metamaterials as a brand‐new research direction and have inspired extensive innovative applications in flexible electronics. Here, such a groundbreaking interdisciplinary field is first coined as “flexible metamaterial electronics,” focusing on enhancing and innovating functionalities of flexible electronics via the design of metamaterials. Herein, the latest progress and trends in this infant field are reviewed while highlighting their potential value. First, a brief overview starts with introducing the combination of metamaterials and flexible electronics. Then, the developed applications are discussed, such as self‐adaptive deformability, ultrahigh sensitivity, and multidisciplinary functionality, followed by the discussion of potential prospects. Finally, the challenges and opportunities facing flexible metamaterial electronics to advance this cutting‐edge field are summarized.

Inkjet printing for preparing quantum dot light emitting diodes (QLEDs) has become increasingly attractive due to its large‐area, low‐cost fabrication features. However, the rather low resolution and coarse morphology induced by the printing and uneven evaporation of droplet restrict its further development. Herein, electrohydrodynamic (EHD) printing and mixed solvent method are employed to fabricate high‐resolution pixelated QLEDs. By optimizing the mixed solvent ratio to weaken capillary flow, coffee‐ring‐free quantum dot (QD) films can be obtained. With the help of EHD printing process optimization and pixel defining layers introduction, high‐resolution pixelated QLED with 306 pixels per in. is achieved, which can meet the requirements of manufacturing mobile phones. Finally, an inverted pixelated QLED with a low turn‐on voltage of 3 V and a maximum luminance of 8533 cd m−2 is fabricated, demonstrating that the presented strategy has huge potential in high‐resolution and high‐quality QD display manufacturing.

Low-cost growth of patterned zinc oxide (ZnO) nanorod arrays (NAs) has attracted much attention with the rapid development of electronics and nanotechnology. Mechanoelectrospinning-assisted continuous hydrothermal synthesis method (MES-CHSM) is proposed to direct-write the precursor patterns for growth of ZnO-NAs, in a digital, low-cost, and mask-free manner. The morphology and distribution of hierarchical ZnO nanorods, having a tremendous impact on gas response, are determined by the process parameters of MES-CHSM. It is highly desirable that the diameter, interval, orientation and distribution of ZnO nanorods can be tuned proactively by changing growth time, solution concentration, the nature of precursor layer, and the pattern by MES. ZnO-NAs exert excellent Ohmic contact with interdigital electrodes when exposure to dry air, NO2 gas and dry air again. The gas response of ZnO sample is surface-reaction-determining. Gas sensing results show highly sensitive and repeatable response-recovery cycles with NO2 gas exposure and the air purge, respectively. The dynamic response of gas sensor shows temperature-dependent response to NO2, even at low concentrations (1-50 ppm). The best gas response is located between 200 ºC and 225 ºC. Gas sensors, prepared by different process parameters, show two laws between the corresponding responses and NO2 concentrations: approximately linear and saturation regions. The optimal process parameters is presented to postpone the occurrence of saturation region, to enlarge measuring range. Please do not adjust marginsPlease do not adjust margins where the MES is an improved electrohydrodynamic direct-writing process with high controllability on the morphology of fibers 32, 33 . This method can achieve highly aligned ZnO nanorods on sub-10micrometer printed patterns, to form hierarchical structures of the highly sensitive sensors. Further, the morphology and distribution of ZnO-NAs are tunable with different process parameters, such as growth time, ZnAc precursor concentration, Zn(NO3)2 concentration in growth solution and the printed micropattern of MES. Their relationships with gas sensing performance are investigated in detail to discover the optimal parameters of process and working. Experimental section PreparationZinc acetate (ZnAc, Zn(CH3COO)22H2O, AR), zinc nitrate (Zn(NO3)2, AR) hydrate and hexamethylenetetramine (HMTA, (CH2)6N4) were purchased from Sinopharm Chemical Reagent Co., Ltd.. Polyethylene oxide (PEO) used in this study was purchased from Aldrich. The relative molecular mass (Mr) of PEO was 600,000. An aqueous solution containing PEO (6wt%) and ZnAc was fabricated by magnetic stirring for 10 hours (h). Aqueous solutions of Zn(NO3)2 (0.2 M) and HMTA (0.2 M) were prepared by magnetic stirring for >0.5 h respectively, then were mixed with equal volume and stirred evenly to fabricated mixed solution of Zn(NO3)2 and HMTA.Interdigitated electrodes of Ag were screen printed on alumina substrate (1 cm*0.8 cm). The distance between adjacent electrodes was 800 µm. Hierarchical...

Curved electronics, which are better coordinated and blended with the natural world due to the characteristics of large contact area, high space adaptability, etc., have been widely used in a quantity of areas ranging from conformal curved antennas and sensors in detection and measurement, to artificial smart skin of aerospace. Recent developments in curved electronics have made an increasing progress to the historic drawbacks of conventional planar electronics, however significant challenges still exist. Here, the main kinds of conformal fabrication technologies, including transfer printing, assembly techniques, curved lithography, conformal inkjet printing, 3D printing, and laser direct writing, are reviewed to realize manufacturing deformable/undeformable electronics on curved or arbitrary surfaces. The processes and features of each technology are comprehensively summarized together with their progress and potential values. Finally, the challenges and opportunities for fabricating conformal electronics on arbitrary surfaces are also discussed.