Full Solution Process Research Articles

Large-Emitting-Area Quantum Dot Light-Emitting Diodes Fabricated by an All-Solution Process.

Quantum dots (QDs) have attracted a lot of attention over the past decades due to their sharp emission spectrum and color, which can be tuned by changing just the particle size and chromophoric stability. All these advantages of QDs make quantum dot light-emitting diodes (QLEDs) promising candidates for display and light-source applications. This paper demonstrates a large-emitting-area QLED fabricated by a full-solution process. This QLED is composed of indium tin oxide (ITO) as the anode, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) as the hole injection layer (HIL), and poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (poly-TPD) as the hole-transport layer (HTL). The light-emitting layer (EML) is composed of green CdSe/ZnS quantum dots. By applying the ZnO nanoparticles as the electron-injection/transport layer, QLED devices are prepared under a full-solution process. The large-emitting-area QLED exhibits a low turn-on voltage of around 2~3 V, and the International Commission on Illumination (CIE) 1931 coordinate value of the emission spectrum was (0.31, 0.66). The large emitting area and the unique QLED structure of the device make it possible to apply these features to inkjet printing quantum dot light sources and quantum dot display applications.

Full Solution Process of a Near-Infrared Light-Emitting Electrochemical Cell Based on Novel Emissive Ruthenium Complexes of 1,10-Phenanthroline-Derived Ligands and a Eutectic Alloy as the Top Electrode

Near-infrared luminescent materials have recently received considerable attention for a large number of applications, including in solid-state lighting, as bioimaging agents, as photovoltaic cells, and in the telecommunication industry. By adding diverse electron-donating or withdrawing groups on ancillary ligands based on benzenethiol-phenanthroline, we synthesized and optoelectronically characterized a series of novel ionic ruthenium complexes, namely RuS, RuSCl, RuSMe, and RuSNH2, for using in a light-emitting electrochemical cell. The synthesized complexes are intense red emitters in the range of 584–605 nm in solution, which depends on the substitutions of electron donor/acceptor moieties on the ancillary ligands. To find a suitable quantum mechanical approach, benchmark calculations based on time-dependent density functional theory were carried out on these complexes. Our benchmark revealed that the M06-L method has results close to those of the experiment. Furthermore, to gain a deeper insight into electronic transitions, several excitation processes were investigated at the TD-DFT-SMD-MN12-L/gen level. The results showed that in the designed complexes, the dominant transition is between the 4dZ2 electron of Ru (particle) and the π* orbitals of the ancillary ligand (hole). The single-layer devices, including these complexes along with a Ga/In cathode by a facile deposition method without the addition of any electron or hole transport layers, were fabricated and displayed red (678 nm) to near-infrared (701 nm) emission as well as a decrease of turn-on voltage from 3.85 to 3.10 V. In particular, adding a methyl group to the ancillary ligand in the complex RuSNH2 increases the external quantum efficiency to 0.55%, one of the highest observed values in the ruthenium phenanthroline family. This simple structure of the device lets us develop the practical applications of light-emitting electrochemical cells based on injection and screen-printing methods, which are very promising for the vacuum-free deposition of top electrodes.

Intrinsically stretchable, semi-transparent organic photovoltaics with high efficiency and mechanical robustness via a full-solution process

AZO@Ag nanowire@AZO (AAA) composite stretchable transparent electrode enables full-solution-processed semi-transparent intrinsically stretchable OPV achieving record 10.90% PCE, with excellent mechanical robustness against stretch-release cycles.

Full solution-processed heavy-metal-free mini-QLEDs for flexible display applications.

Micro/mini displays play an extremely significant role in the modern information society, which is treated as a promising technology for a range of applications. Here, utilizing the full solution process with the electrode array mask, we successfully achieved passive-matrix and active-matrix mini-quantum dot light-emitting diodes (PM/AM-m-QLEDs) based on heavy-metal-free blue ZnTeSe/ZnS QDs. The pixels per inch (PPI) of m-QLEDs fabricated in this study can reach 36, 90, 180, and 360, which meet the requirements of televisions, computers, and mobile phones. Moreover, by adjusting the electrodes, m-QLEDs achieved patterned display applications based on both flexible and solid substrates. These results imply that heavy-metal-free blue m-QLEDs show a wide display application potential, i.e., AM/PM displays. Given the low-cost advantage of solution-processed QDs, our proposed techniques could pave the way for low-cost displays.

All-Solution-Processed Molybdenum Oxide-Encapsulated Silver Nanowire Flexible Transparent Conductors with Improved Conductivity and Adhesion.

A novel transparent conductive conductor composed of a silver nanowire (AgNW) network and MoOx on a flexible polyethylene terephthalate (PET) substrate, with contemporaneously improved adhesion and reduced resistivity, is prepared using the full-solution process without high-temperature annealing. Under the optimized conditions, a MoOx/AgNW/MoOx multilayer is achieved, which shows much superior optoelectronic performance to that obtained from ITO with a high optical transmittance of 89.2% and a low sheet resistance of ∼12.5 Ω/sq. Unlike pure AgNW films, the sheet resistance is little changed after the tape and ultrasonication tests, illustrating a very strong adhesion to the PET substrate after the encapsulation of MoOx. Moreover, the multilayer film exhibits excellent stability to resist mechanical bending and acid damage. In addition, the successful implementation of the flexible transparent heater demonstrates the practical application value of the electrode.

A transparent flexible volatile memory with ultrahigh ON/OFF ratio and ultralow switching voltage

Here, a high-performance transparent flexible dynamic random access memory (DRAM) device on a polyvinyl alcohol (PVA) substrate is presented with silver nanowires (Ag NWs) serving as top and bottom electrodes, and hybrid silver nanoparticles (Ag NPs)-polyvinyl pyrrolidone (PVP) films serve as resistive-switching (RS) medium. The obtained memory cells show typical volatile RS behaviors with an ultrahigh ON/OFF current ratio of 10 8 and an ultralow switching voltage of 0.7 V. In particular, the fabricated flexible devices demonstrate excellent mechanically robust feature and great electrical stability during 100 dynamic bending tests, maintaining ~85% of transparency in the visible wavelength. This work provides an effective route to construct flexible and transparent polymer memory devices with high-performance. A transparent flexible polymer memory consisting of polyvinylpyrrolidone-silver nanoparticle composite switch sandwiched between silver nanowire electrodes with polyvinyl alcohol substrate was fabricated via a full solution method. The obtained device exhibited a high-performance volatile memory behavior with ultralow switching voltage and ultrahigh ON/OFF ratio as well as outstanding transparency and flexibility. • A high performance transparent flexible DRAM-type polymer memory was achieved. • The memory device was prepared basing on a full-solution processing method. • High OFF/ON current ratio of ~10 8 and low switching voltage of ~0.7 V was achieved. • Silver nanowires (Ag NWs) is essential for excellent transparency and flexibility.

All-solution-processed colour-tuneable tandem quantum-dot light-emitting diode driven by AC signal.

We demonstrate a novel structure for a quantum-dot light-emitting diode (QD-LED) with wide-range colour-tuneable pixels, fabricated via full solution processing. The proposed device has a symmetrical structure produced via stacking of an inverted-structure diode with a green QD emission layer (EML) and normal-structure diode with a red QD EML. It is an electron-only device; however, a charge generation layer in the middle of the device generates holes for the formation of excitons. Depending on the polarity of the applied voltage, either the bottom inverted unit or the top normal unit is operated, thereby emitting green or red light, respectively. The working mechanism of the device is investigated via analysis of the charge generation mechanism and carrier transport path. In addition, the colour tunability is verified using a simple alternating current (AC) driving scheme; the duty cycle modulation of the AC signal enables fine colour adjustment over a broad range, from pure green to pure red. Thus, our colour-tuneable QD-LED with vertically stacked independently operated sub-pixels can open a promising pathway towards cost-effective ultra-high-resolution displays.

High-performance thermoelectric silver selenide thin films cation exchanged from a copper selenide template.

Over the past decade, Ag2Se has attracted increasing attention due to its potentially excellent thermoelectric (TE) performance as an n-type semiconductor. It has been considered a promising alternative to Bi–Te alloys and other commonly used yet toxic and/or expensive TE materials. To optimize the TE performance of Ag2Se, recent research has focused on fabricating nanosized Ag2Se. However, synthesizing Ag2Se nanoparticles involves energy-intensive and time-consuming techniques with poor yield of final product. In this work, we report a low-cost, solution-processed approach that enables the formation of Ag2Se thin films from Cu2−xSe template films via cation exchange at room temperature. Our simple two-step method involves fabricating Cu2−xSe thin films by the thiol-amine dissolution of bulk Cu2Se, followed by soaking Cu2−xSe films in AgNO3 solution and annealing to form Ag2Se. We report an average power factor (PF) of 617 ± 82 μW m−1 K−2 and a corresponding ZT value of 0.35 at room temperature. We obtained a maximum PF of 825 μW m−1 K−2 and a ZT value of 0.46 at room temperature for our best-performing Ag2Se thin-film after soaking for 5 minutes. These high PFs have been achieved via full solution processing without hot-pressing.

Bilayer nanocarbon heterojunction for full-solution processed flexible all-carbon visible photodetector

Low-dimensional carbon nanomaterials have emerged as promising materials for optoelectronic devices, fueled by their predominant optical and electronic properties. Herein, by utilizing a bilayer nanocarbon heterojunction comprising one dimensional (1D) single-walled carbon nanotubes and zero dimensional (0D) fullerenes (C60), a flexible all-carbon visible photodetector consisting of the bilayer nanocarbon heterojunction onto parallel dimethyl sulfoxide -doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) electrodes is fabricated on a polyethylene terephthalate substrate via the full-solution process. The obtained photodetector exhibits excellent air-stable photosensitivity under the visible light condition with a high light/dark current ratio, which is attributed to the efficient separation of photogenerated electron-hole pairs at the interface of the bilayer heterojunction. Moreover, the photodetector shows stable photoresponse during the bending test with a small bending radius owing to its intrinsic flexible properties of each component. This work affords new opportunities for high-throughput fabrication of next-generation flexible carbon electronics toward greener electronics.

Transient Light Emitting Devices Based on Soluble Polymer Composites

Building transient electronics are promising and emerging strategy to alleviate the pollution issues from electronic waste (e-waste). Although a variety of transient devices comprising organic and inorganic materials have been described, transient light emitting devices are still elusive but highly desirable because of the huge amount of lighting and display related consumer electronics. Here we report a simple and efficient fabrication of large-area flexible transient alternating current electroluminescent (ACEL) device through a full-solution processing method. Using transparent flexible AgNW-polymer as both electrodes, the devices exhibit high flexibility and both ends side light emission, with the features of controlled size and patterned structure. By modulating the mass ratio of blue and yellow phosphors, the emission color is changed from white to blue. Impressively, the fabricated ACEL device can be thoroughly dissolved in water within 30 min. Our strategy combining such advances in transient light emitting devices with simple structure, widely used materials, full solution process, and high solubility will demonstrate great potential in resolving the e-waste from abandoned light-emitting products and expand the opportunities for air-stable flexible light emitting devices.

Buffer layer control for solution processing of white organic light-emitting diodes

Inverted structure white organic light-emitting diodes were fabricated via full solution processing with a functional buffer layer. The single emissive layer was composed of a blend of host and transporting materials (both hole and electron) doped with blends of blue and red phosphors. A mixed-host system was used to improve the device performances by lowering the energy barriers of the transporting layer to the emissive layer. The effect of the composition of transporting materials on the performance of solution processed organic light-emitting diodes was investigated. An ultra-thin physisorbed buffer layer was used for charge injection balance. A PEDOT layer was blended with polyvinyl alcohol and other additives in order to prevent penetration by silver paste into the emissive layer. White organic light-emitting diodes were fabricated with a luminance efficiency of 0.016 lm/W and balanced white light with CIE coordinates of (0.31, 0.33).

Solution-processed multifunctional transparent conductive films based on long silver nanowires/polyimide structure with highly thermostable and antibacterial properties

The optical, electrical, thermal and antibacterial properties of AgNW/PI composite films.

Well-controlled silver nanowire/graphene hybrid from full solution process

The surface of a one-dimensional silver nanowire was covered with amphiphilic materials, N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide, and patched with two-dimensional graphene to form individually controlled hybrid. Graphene was prepared from ultrasonic in o-dichlorobenzene without any additives. As N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide between silver nanowires and graphene tightly held each other, silver nanowire was individually covered with graphene without introducing ultrasonic power, the necessary process to evenly mix silver nanowires and graphene but lead to damage and oxidize silver nanowires. Although the quality of graphene was inferior, the properties of hybrid were superior compared with pristine silver nanowire/graphene except introducing N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide. All processes to form the hybrid were carried out in solution. Therefore, this makes the processes less expensive and more useful and opens up opportunities for the mass production for conductive materials.

Wearable Electricity Generators Fabricated Utilizing Transparent Electronic Textiles Based on Polyester/Ag Nanowires/Graphene Core-Shell Nanocomposites.

The technological realization of wearable triboelectric generators is attractive because of their promising applications in wearable self-powered intelligent systems. However, the low electrical conductivity, the low electrical stability, and the low compatibility of current electronic textiles (e-textiles) and clothing restrict the comfortable and aesthetic integration of wearable generators into human clothing. Here, we present high-performance, transparent, smart e-textiles that employ commercial textiles coated with silver nanowire/graphene sheets fabricated by using a scalable, environmentally friendly, full-solution process. The smart e-textiles show superb and stable conduction of below 20 Ω/square as well as excellent flexibility, stretchability, foldability, and washability. In addition, wearable electricity-generating textiles, in which the e-textiles act as electrodes as well as wearable substrates, are presented. Because of the high compatibility of smart e-textiles and clothing, the electricity-generating textiles can be easily integrated into a glove to harvest the mechanical energy induced by the motion of the fingers. The effective output power generated by a single generator due to that motion reached as high as 7 nW/cm(2). The successful demonstration of the electricity-generating glove suggests a promising future for polyester/Ag nanowire/graphene core-shell nanocomposite-based smart e-textiles for real wearable electronic systems and self-powered clothing.

Self-aligned, full solution process polymer field-effect transistor on flexible substrates.

Conventional techniques to form selective surface energy regions on rigid inorganic substrates are not suitable for polymer interfaces due to sensitive and soft limitation of intrinsic polymer properties. Therefore, there is a strong demand for finding a novel and compatible method for polymeric surface energy modification. Here, by employing the confined photo-catalytic oxidation method, we successfully demonstrate full polymer filed-effect transistors fabricated through four-step spin-coating process on a flexible polymer substrate. The approach shows negligible etching effect on polymeric film. Even more, the insulating property of polymeric dielectric is not affected by the method, which is vital for polymer electronics. Finally, the self-aligned full polymer field-effect transistors on the flexible polymeric substrate are fabricated, showing good electrical properties and mechanical flexibility under bending tests.

Flip-flop logic circuit based on fully solution-processed organic thin film transistor devices with reduced variations in electrical performance

Organic reset–set (RS) flip-flop logic circuits based on pseudo-CMOS inverters have been fabricated using full solution processing at a relatively low process temperatures of 150 °C or less. The work function for printed silver electrodes was increased from 4.7 to 5.4 eV through surface modification with a self-assembled monolayer (SAM) material. A bottom-gate, bottom-contact organic thin-film transistor (OTFT) device using a solution-processable small-molecular semiconductor material exhibited field-effect mobility of 0.40 cm2 V−1 s−1 in the saturation region and a threshold voltage (VTH) of −2.4 V in ambient air operation conditions. In order to reduce the variations in mobility and VTH, we designed a circuit with six transistors arranged in parallel, in order to average out their electrical characteristics. As a result, we have succeeded in reducing these variations without changing the absolute values of the mobility and VTH. The fabricated RS flip-flop circuits were functioned well and exhibited short delay times of 3.5 ms at a supply voltage of 20 V.

Perovskite/polymer monolithic hybrid tandem solar cells utilizing a low-temperature, full solution process

In the current study, a monolithic integration of perovskite and polymer subcells into a tandem structure is realized through a full solution process.

Spatial element distribution control in a fully solution-processed nanocrystals-based 8.6% Cu2ZnSn(S,Se)4 device.

A fully solution-processed high performance Cu2ZnSn(S,Se)4 (CZTSSe, kesterite) device has been demonstrated. It is based on the rational engineering of elemental spatial distributions in the bulk and particularly near the surface of the film from nanocrystal precursors. The nanocrystals are synthesized through a modified colloidal approach, with excellent solubility over a large compositional window, followed by a selenization process to form the absorber. The X-ray photoluminescence (XPS) depth profiling indicates an undesirable Sn-rich surface of the selenized film. An excessive Zn species was quantitatively introduced through nanocrystals precursor to correct the element distribution, and accordingly a positive correlation between the spatial composition in the bulk/surface film and the resulting device parameter is established. The enhanced device performance is associated with the reduced interfacial recombination. With a Zn content 1.6 times more than the stoichiometry; the optimized device, which is fabricated by employing a full solution process from the absorber to the transparent top electrode, demonstrates a performance of 8.6%. This composition-control approach through stoichiometric adjustments of nanocrystal precursors, and the developed correlation between the spatial composition and device performance may also benefit other multielement-based photovoltaics.

Polymer‐Assisted Metal Deposition (PAMD): A Full‐Solution Strategy for Flexible, Stretchable, Compressible, and Wearable Metal Conductors

Metal interconnects, contacts, and electrodes are indispensable elements for most applications of flexible, stretchable, and wearable electronics. Current fabrication methods for these metal conductors are mainly based on conventional microfabrication procedures that have been migrated from Si semiconductor industries, which face significant challenges for organic-based compliant substrates. This Research News highlights a recently developed full-solution processing strategy, polymer-assisted metal deposition (PAMD), which is particularly suitable for the roll-to-roll, low-cost fabrication of high-performance compliant metal conductors (Cu, Ni, Ag, and Au) on a wide variety of organic substrates including plastics, elastomers, papers, and textiles. This paper presents i) the principles of PAMD, and how to use it for making ii) flexible, stretchable, and wearable conductive metal electrodes, iii) patterned metal interconnects, and d) 3D stretchable and compressible metal sponges. A critical perspective on this emerging strategy is also provided.

Phosphoryl/Sulfonyl-Substituted Iridium Complexes as Blue Phosphorescent Emitters for Single-Layer Blue and White Organic Light-Emitting Diodes by Solution Process

Two new phosphoryl/sulfonyl-substituted iridium complexes, POFIrpic and SOFIrpic, have been designed and synthesized on the basis of the structural frame of sky-blue FIrpic. The introduction of phosphoryl/sulfonyl moieties into the 5′-position of phenyl ring makes the emission peak blue-shift to the 460 nm, simultaneously the compounds maintain high photoluminescence quantum yields (PLQYs) of about 50% in solution. Single-layer blue and white polymer organic light-emitting diodes by full solution-process were fabricated with the following configuration: ITO/PEDOT:PSS/PVK:OXD-7:dopants/CsF/Al. The blue device based on POFIrpic shows a maximum current efficiency of 11.1 cd A–1, a maximum external quantum efficiency of 7.1%, which are the highest ever reported for blue PhOLEDs by full solution process. The white device with POFIrpic as blue component reveals a maximum current efficiency of 25 cd A–1, a maximum external quantum efficiency of 15%, and a good CRI value of 82.