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Electronic thin films play a ubiquitous role in microelectronic devices and especially hold great promise for flexible electronics, energy conversion and storage, and biomedical applications. Their characterizations, including ultra‐thin, large‐scale dimensions, stretchability, and conformal ability to curved or 3D structures, present new challenges for thin film fabrication based on the solution method. Electrospray deposition emerges as a feasible method for fabricating large‐area, flexible, and curved films. It offers many advantages such as material adaptability, controlled atomization, tunable film morphology, and shape retention on complex substrates. These advantages make it a key method for fabricating high‐performance films on large‐area, 3D surfaces. This work presents a comprehensive review of the mechanisms, processes, applications, and equipment of electrospray deposition. First, the fundamental principles of electrospray deposition are introduced, focusing on the mechanisms and scaling laws of liquid atomization. Moreover, the control methods for electrospray modes, structures, and film morphology are discussed. These advanced control methods pave the way for the fabrication of smart skins, wearable devices, and energy conversion and storage components. Finally, this work introduces three types of electrospray deposition manufacturing equipment to illustrate the advantages of electrospray deposition for large‐area, and 3D surface manufacturing. [ABSTRACT FROM AUTHOR]

The dynamic response of a micrometer-sized gallium–indium (Ga-In) jet in nitrogen subjected to intense Neodymium-doped Yttrium Aluminum Garnet (Nd: YAG) laser pulses with energy ranging from 0.35 to 5.0 mJ per pulse is investigated experimentally. The rapid deformation of the jet was visualized using timed-delayed stroboscopic shadowgraphy. The laser pulse disrupts the jet to form a gap, and the length of the gap grows according to a logarithm relationship with respect to the dimensionless time normalized a characteristic timescale τ, which is determined by the pulse energy Ep. The ablation impulse bends and flattens the jet into a thin curved film that resembles a wind-blown sail. The area of the sail increases with t6/5Ep13/15, where t is time. The sail eventually breaks up into fine mist. Additionally, we found that the laser-blast-induced initial bending velocity of the jet could be predicted using the semi-empirical laser-ablated propulsion model for an In-Sn droplet of tens of micrometers. [ABSTRACT FROM AUTHOR]

Colloidal PbS quantum dots (QDs) have attracted tremendous attention in near‐infrared photodetection for their superior optoelectronic properties. However, appropriate fabrication methods remain a challenge for scalable and high performance PbS QD photodetectors. Herein, a flexible microcomb printing (FMCP) technique is first introduced to fabricate PbS QD photoconductors without a layer‐by‐layer ligand exchange technique, and the detectors demonstrate a responsivity of 2.1 A W−1. A computational fluid dynamics model is built to simulate the flow field distribution and analyze the relationship between the key parameters of FMCP and QD film morphology. The QD ink flow field at the tip of the microcomb exhibits high shear rates that lead to a better crystallization configuration for solid QD films formation, which is verified by Grazing‐incidence small and wide‐angle X‐ray scattering. Moreover, the relationship between the intrinsic nature of the QD ink (viscosity and surface tension), substrate temperature, and printing speed are systematically analyzed to experimentally achieve high performance QD films. Benefiting from the good crystallization configuration, FMCP‐printed photodetectors using the direct PbS QD ink without ligand exchange show high responsivities. The results indicate that FMCP is a promising method for scalable and high‐performance PbS QD photodetectors. [ABSTRACT FROM AUTHOR]

The research on new functional layer materials and optimization of fabrication in organic light-emitting diode (OLED) has been continuously concerned. In this work, phosphotungstic acid solution used as a precursor is spin-coated onto ITO anode, and then a phosphorus-tungsten oxide (WO 3 -P 2 O 5 ) film is obtained after annealing treatment. Various parameters which include film composition, surface morphology, work function and optical property are measured. It suggests that the film has the composition of 24 WO 3 ·P 2 O 5 annealed at 200 °C, which exhibits work function of 5.55 eV, surface root mean square (RMS) roughness value of 1.525 nm and optical transmittance of over 92%. The WO 3 -P 2 O 5 film is used as hole injection layer (HIL), and the OLED with the structure of [ITO/ WO 3 -P 2 O 5 / TPD/ Alq 3 / LiF/ Al] is fabricated. The performance of device shows turn-on voltage of 2.6 V, maximum luminance of 13553 cd/m 2 , maximum current efficiency of 5.87 cd/A and maximum power efficiency of 3.44 lm/W, respectively. The results provide a new way to deposit HIL based on solution-processed metal oxide in efficient OLED. [ABSTRACT FROM AUTHOR]

Top electrodes of organic photovoltaics (OPVs) are usually thermally evaporated in the vacuum, which is non‐continuous and time‐consuming and has been the bottleneck for the OPV fabrication process. Printable top electrodes that are free of vacuum, high temperature, and solvents will make OPVs more attractive. Low‐melting‐point alloys (LMPAs) are promising candidates for printable OPV electrodes thanks to the merits of matching work functions, high electron conductivity, high environment stability, and no need for post‐treatment. Here, LMPA electrodes are directly deposited on OPVs by simply falling a single LMPA droplet onto the substrate. The LMPA droplet spreads to form a thin film with a smooth interface intimately contacting the substrate. The electrode area can be tailored by adjusting the droplet diameter or the Weber number, which is the ratio of inertia to surface tension. The interface morphology is mainly affected by the contact temperature. The degree of oxidation and charges on the droplet can also influence the electrode area and interface morphology. OPVs with droplet‐impacted LMPA electrodes exhibit power conversion efficiencies of up to 16.17%. This work demonstrates the potential of single‐droplet impact deposition as a simple method for printing OPV electrodes for scalable manufacturing. [ABSTRACT FROM AUTHOR]

Organic semiconductor (OSC) films fabricated by meniscus‐guided coating (MGC) methods are suitable for cost‐effective and flexible electronics. However, achieving crystalline thin films by MGC methods is still challenging because the nucleation and crystal growth processes are influenced by the intertwined interactions among solvent evaporation, stochastic nucleation, and the fluid flow instabilities. Herein, a novel flexible fountain pen with active ink supply is designed and used to print OSCs. This direct‐write method allows the flexible pen tip to contact the substrate, maintaining a robust meniscus by eliminating the gap found in conventional MGCs. An in situ optical microscopy observation system shows that the precursor film plays a critical role on the crystallization and the formation of coffee rings and dendrites. The computational fluid dynamics simulations demonstrate that the microstructure of the pen promotes extensional flows, facilitating mass transport and crystal alignment. Highly‐aligned ribbon‐shaped crystals of a small organic molecule (TIPS‐pentacene), as well as a semiconducting polymer (N2200) with highly‐ordered orientations, have been successfully printed by the flexible fountain pen. Organic field‐effect transistors based on the flexible pen printed OSCs exhibit high performances and strong anisotropic mobility. In addition, the flexible fountain pen is expandable for printing multiple lines or large‐area films. [ABSTRACT FROM AUTHOR]

Thin films deposited by conventional electrospray of volatile solutions often give rise to rough morphology consisting of "coffee rings" formed by individual sessile droplets. This is due to the long average inter-droplet distance and low merging probability of deposited droplets within the sprayed circular area. We present a quadrupole configuration to form a squeezing electric field that compresses the circular electrospray pattern into a much slenderer elliptical shape. The design is validated by tracking the trajectories of all sprayed droplets using the Lagrangian method. Moreover, the statistical study of the deposited droplet merging process and experimental results prove that the quadrupole configuration can dramatically decrease inter-droplet distance and increase the merging probability of deposited droplets. The simple apparatus offers precise controls of the aspect ratio of the pattern and provides a feasible approach to produce smooth thin films without pin holes. • A quadrupole configuration is presented to produce the deposited patterns of high aspect ratios in electrospray. • Trajectories of sprayed charged droplets are simulated using the Lagrangian model. • The quadrupole configuration can dramatically increase droplet merging probability for producing smooth thin films. [ABSTRACT FROM AUTHOR]