Solution-processed Technology Research Articles

Total solution processable and low-cost DNA methylation sensor

DNA methylation sensor is an emerging demand of modern medical for laboratory, though lots of efforts have been contributed in this discipline, the easy-to-operate and efficient sensing terminal is still in deficiency. In this work, a total solution processable printing technology is proposed to fabricate the DNA methylation sensor, which is based on the liquid gate graphene field effect transistor (Lg-GFET). Meanwhile, the graphene ink (G-ink) was prepared by using the modified liquid-exfoliation method, to facilitate printing production. Then, five kinds of tested single strand DNA (ssDNA) which have 0 to 4 5-methylcytosine (5mC) sites were covalently anchored on the graphene channel. X-ray photoelectron spectroscopy (XPS) was conducted to demonstrate the analyte ssDNA was successfully fixed. Thirdly, the 5mC sites were identified by their antibody of 5mC (5mCab) and transduced as the changed current between the source and drain electrodes ( I ds). It is found the proposed sensor has good linear sensitivity (about -1.68% for per 5mC) to the amount of 5mC sites on the tested ssDNAs with Pearson correlation coefficient -0.98 and excellent anti-interference to unmethylated ssDNAs. Besides, the cost is estimated to be about $ 1.5 for each of the proposed DNA methylation sensor. Conclusively, the proposed low-cost component may be an efficient candidate for promoting the instant DNA methylation determination.

Impedimetric, PEDOT:PSS-Based Organic Electrochemical Sensor for Detection of Histamine for Precision Animal Agriculture

High concentrations of histamine are associated with subacute ruminal acidosis, a common disease in high-producing lactating dairy cows. Therefore, the accurate detection of low histamine levels is a strategy to monitor and diagnose ruminal acidosis in early stages. In this letter, we have developed an impedimetric histamine biosensor based on an organic semiconductor: poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). It can be utilized to detect low concentrations of histamine in a phosphate-buffered saline (PBS) buffer and McDougall's buffer solution (MDBS) with an impedimetric readout technique. With PEDOT:PSS film as the sensing medium, the device displayed a limit of detection of 0.1 μM and an impedance of ∼82 Ω at low frequencies in MDBS. The impedance is correlated with the concentration of histamine: the R2 values in the PBS (pH = 5.5 and pH = 7.4) and the MDBS (pH = 8.4) are 0.95, 0.95, and 0.99, respectively. The sensor is fabricated using large-area solution processing technology, opening the door to low-cost, high-volume commercial sensor production.

Alkyl-Substituted Selenium-Bridged V-Shaped Organic Semiconductors Exhibiting High Hole Mobility and Unusual Aggregation Behavior.

Toward the development of high-performance organic semiconductors (OSCs), carrier mobility is the most important requirement for next-generation OSC-based electronics. The strategy is that OSCs consisting of a highly extended π-electron core exhibit two-dimensional (2D) aggregated structures to offer effective charge transport. However, such OSCs, in general, show poor solubility in common organic solvents, resulting in limited solution processability. This is a critical trade-off between the development of OSCs with simultaneous high carrier mobility and suitable solubility. To address this issue, herein, five-membered ring-fused selenium-bridged V-shaped binaphthalene with decyl substituents (C10-DNS-VW) is developed and synthesized by an efficient method. C10-DNS-VW exhibits significantly high solubility for solution processes. Notably, C10-DNS-VW forms a one-dimensional π-stacked packing motif (1D motif) and a 2D herringbone (HB) packing motif (2D motif), depending on the crystal growth condition. On the other hand, the fabrication of thin films by means of both solution process and vacuum deposition techniques forms only the 2D HB motif. External stress tests such as heating and exposure to solvent vapor indicated that 1D and 2D motifs could be synergistically induced by the total balance of intermolecular interactions. Finally, the single-crystalline films of C10-DNS-VW by solution process exhibit carrier mobility up to 11 cm2 V-1 s-1 with suitable transistor stability under ambient conditions for more than two months, indicating that C10-DNS-VW is one of the most promising candidates for breaking the trade-off in the field of solution-processed technologies.

Silver and copper nanowire films as cost-effective and robust transparent electrode in energy harvesting through photovoltaic: A review

Presently, there is a high demand for cost-effective, solution-processed technology for fabrication of thin-film solar cell to compete with the well-stabilised Si-solar cell at industrial scale. In thin-film solar cell, the active layers such as absorber and interfacial layer can be deposited by a cost-effective chemical route but the transparent electrode, which is generally ITO, is deposited using vacuum-based expensive technology. To minimize the overall fabrication cost of thin-film solar cell, in addition to absorber and interfacial layers, the deposition of solution-processed transparent electrode is also required. To replace ITO, researcher have given major efforts to apply solution-processed Ag and Cu nanowire networks as transparent electrode owing to their excellent conductivity and transmittance. In this review, we present recent advances in the application of Ag and Cu nanowire-based transparent electrode in photovoltaic. The inherent issues pertaining to application of nanowire-based transparent electrode in fabrication of organic and perovskite solar cells is addressed.

Facile Synthesis of Solution-Processed Silica and Polyvinyl Phenol Hybrid Dielectric for Flexible Organic Transistors.

A high-quality dielectric layer is essential for organic thin-film transistors (OTFTs) operated at a low-power consumption level. In this study, a facile improved technique for the synthesis of solution-processed silica is proposed. By optimizing the synthesis and processing technique fewer pores were found on the surface of the film, particularly no large holes were observable after improving the annealing process, and the improved solution–gelation (sol–gel) SiOx dielectric achieved a higher breakdown strength (1.6 MV/cm) and lower leakage current density (10−8 A/cm2 at 1.5 MV/cm). Consequently, a pentacene based OTFT with a high field effect mobility (~1.8 cm2/Vs), a low threshold voltage (−1.7 V), a steeper subthreshold slope (~0.4 V/dec) and a relatively high on/off ratio (~105) was fabricated by applying a hybrid gate insulator which consisted of improved sol–gel SiOx and polyvinyl phenol (PVP). This could be ascribed to both the high k of SiOx and the smoother, hydrophobic dielectric surface with low trap density, which was proved by atomic force microscopy (AFM) and a water contact angle test, respectively. Additionally, we systematically studied and evaluated the stability of devices in the compressed state. The devices based on dielectric fabricated by conventional sol–gel processes were more susceptible to the curvature. While the improved device presented an excellent mechanic strength, it could still function at the higher bending compression without a significant degradation in performance. Thus, this solution-process technology provides an effective approach to fabricate high-quality dielectric and offers great potential for low-cost, fast and portable organic electronic applications.

Switchable Multi-Color Solution-Processed QD-laser

In this paper, for the first time, the switchable two-color quantum dot laser has been realized considering solution process technology, which has both simultaneous and lonely lasing capability exploiting selective energy contacts. Furthermore, both channels can be modulated independently, which is a significant feature in high-speed data transmission. To this end, utilizing superimposed quantum dots with various radii in the active layer provides the different emission wavelengths. In order to achieve the different sizes of QDs, solution process technology has been used as a cost-effectiveness and fabrication ease method. Moreover, at the introduced structure to accomplish the idea, the quantum wells are used as separate selective energy contacts to control the lasing channels at the desired wavelength. It makes the prominent device have simultaneous lasing at different emission wavelengths or be able to lase just at one wavelength. The performance of the proposed device has been modeled based on developed rate equation by assuming inhomogeneous broadening of energy levels as a consequence of the size distribution of quantum dots and considering tunnel injection of carriers into the quantum dots via selective energy contacts. Based on simulation results, the simultaneous lasing in both or at one of two wavelengths 1.31 μm and 1.55 μm has been realized by the superimposition of two different sizes of InGaAs quantum dots in a single cavity and accomplishment of selective energy contacts. Besides, controlling the quantum dot coverage leads to managing the output power and modulation response at the desired wavelengths. By offering this idea, one more step is actually taken to approach the switchable QD-laser by the simple solution process method.

PbS colloidal quantum dots patterning technique with low vertical leakage current for the photodetection applications

The colloidal quantum dots (CQDs) are a promising nanometer-sized material system for optoelectronic applications due to the low cost, room temperature processing and substrate compatibility. Solution-processed technology such as spin-coating can make CQDs large-scale deposition on the substrates, whereas it inevitably brings about CQDs adherence to the edges even bottom of the substrates. As a result, the devices are not isolated and vertical leakage current occurs from the surface of CQDs to the substrates. In this work, two kinds of CQDs patterning techniques named etching-assisted patterning (EAP) and lift-off assisted patterning (LAP) have been put forward to significantly suppress the vertical current from several nanoampere to a few picoampere. Meanwhile, the CQDs photoconductor detectors have also been fabricated through these two patterning methods on the SiO2/Si substrates. Compared with un-patterning (UP) photodetectors, these two techniques both can enhance the photocurrent and promote the optoelectrical quality factors such as the responsivity and the specific detectivity, which make it possible to manufacture CQDs detector arrays and promote CQDs in optoelectronic applications.

Recent advances in solution-processed photodetectors based on inorganic and hybrid photo-active materials.

Due to their excellent and tailorable optoelectronic performance, low cost, facile fabrication, and compatibility with flexible substrates, solution-processed inorganic and hybrid photo-active materials have attracted extensive interest for next-generation photodetector applications. This review gives a comprehensive compilation of solution-processed photodetectors. The basic structures of the device and important parameters of photodetectors will be firstly summarized. Then the development of various solution processing technologies containing solution synthesis and liquid phase film-forming processes for the preparation of semiconductor films is described. From the materials science point of view, we give a comprehensive overview about the current status of solution processed semiconductor materials including inorganic and hybrid photo-active materials for the application of photodetectors. Moreover, challenges and future trends in the field of solution-processed photodetectors are proposed.

Multi-wavelength solution-processed quantum dot laser

In this paper, the multi-wavelength solution-processed quantum dot laser has been proposed by the superimposed quantum dots. To this end, the rate equation framework has been developed to model the simultaneous lasing in desired wavelengths by considering inhomogeneous broadening of energy level as a result of the size distribution of quantum dots and the homogeneous broadening due to the carries scattering inside quantum dots. Moreover, the solution process technology has been utilized in order to synthesize the quantum dots in various sizes according to the desired wavelengths. The simulation results show that simultaneous lasing has been realized by superimposition of two sizes of InGaAs quantum dots in a single cavity at two wavelengths of 1.31μm and 1.55μm which have special importance in telecommunication applications. Besides, the output power intensity at the desired wavelengths can be managed by controlling the density of quantum dots.

Ultra-broadband Optical Gain Engineering in Solution-processed QD-SOA Based on Superimposed Quantum Structure

In this work, the optical gain engineering of an ultra-broadband InGaAs/AlAs solution-processed quantum dot (QD) semiconductor optical amplifier using superimposed quantum structure is investigated. The basic unit in the proposed structure (QDs) is designed and fabricated using solution-processed methods with considerable cost-effectiveness, fabrication ease, and QDs size tunability up to various limits (0.1 nm up to the desired values), considering suitable synthesis methods. Increasing the number of QDs, the device can span more than 1.02 μm (O, C, S, and L bands) using only one type of material for all QDs, and is not restricted to this limit in case of using more QD groups. Also, it can manipulate the optical gain peak value, spectral coverage, and resonant energy for customized optical windows, among which 1.31 μm and 1.55 μm are simulated as widely-applicable cases for model validation. This makes the device a prominent candidate for ultra-wide-bandwidth and also customized-gain applications in general. Variation impact of homogeneous and inhomogeneous broadenings, injection current and number of QD groups on optical gain are explained in detail. Besides proposing a design procedure for implementation of an ultra-broadband optical gain using superimposed QDs in solution-processed technology, the proposed gain engineering idea using this technology provides practically infinite bandwidth and an easy way to realize. By introducing this idea, one more step is actually taken to approach the effectiveness of solution process technology.

Building Solar Cells from Nanocrystal Inks

The use of solution-processed photovoltaics is a low cost, low material-consuming way to harvest abundant solar energy. Organic semiconductors based on perovskite or colloidal quantum dot photovoltaics have been well developed in recent years; however, stability is still an important issue for these photovoltaic devices. By combining solution processing, chemical treatment, and sintering technology, compact and efficient CdTe nanocrystal (NC) solar cells can be fabricated with high stability by optimizing the architecture of devices. Here, we review the progress on solution-processed CdTe NC-based photovoltaics. We focus particularly on NC materials and the design of devices that provide a good p–n junction quality, a graded bandgap for extending the spectrum response, and interface engineering to decrease carrier recombination. We summarize the progress in this field and give some insight into device processing, including element doping, new hole transport material application, and the design of new devices.

Simply Structured Near-Infrared Emitters with a Multicyano Linear Acceptor for Solution-Processed Organic Light-Emitting Diodes.

Near-infrared (NIR) organic light-emitting diodes (OLEDs) show great potential in a variety of applications including sensors, night vision, and information security. Despite the superiority of thermally activated delayed fluorescence (TADF) in 100 % exciton harvesting, the development of NIR TADF OLEDs is still a great challenge, especially in terms of solution-processing technology. In this work, a multicyano acceptor of 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofurance (TCF) with strong electron-withdrawing ability was employed to construct solution-processible NIR emitters, CzTCF and tBCzTCF, with the feature of donor-π-acceptor (D-π-A) structure. The significantly enhanced intermolecular charge transfer effects not only render the deep-red and NIR emissions of CzTCF and tBCzTCF films, respectively, but also lead to their typical TADF characteristics. Consequently, the nondoped solution-processed NIR OLED based on tBCzTCF was successfully demonstrated with the peak wavelength of 715 nm, which paves the way for developing NIR emitters without polycyclic aromatic cores and heavy-metal ions.

Functionalized Carbon Nanotube Sensors for the Detection of Sub-ppm Nitric Oxide Gas

In this paper, we demonstrate the highly sensitive carbon nanotube (CNT) sensors for the detection of sub-ppm nitric oxide (NO) gas operating at room temperature. Such achievement can be realized by functionalizing CNT thin films with amine-based polymers through a solution-process technology at low temperature. In addition to high sensitivity, functionalized CNT sensors exhibit high selectivity towards NO gas, which is an effective and practical factor for health-care monitoring nano-electronics. We also investigated the effect of a post-cleaning treatment on the sensing performance of functionalized CNT thin films for sub-ppm NO gas sensors. We believe that this work can open-up new routes to realize high performance human-interactive electronics for respiratory diseases detection in exhaled air.

Water-based processed and alkoxide-based processed indium oxide thin-film transistors at different annealing temperatures**Project supported by the National Natural Science Foundation of China (Grant No. 61675024) and the National Basic Research Program of China (Grant No. 2014CB643600).

In this study, indium oxide (In2O3) thin-film transistors (TFTs) are fabricated by two kinds of low temperature solution-processed technologies (), i.e., water-based (DIW-based) process and alkoxide-based (2-ME-based) process. The thickness values, crystallization properties, chemical structures, surface roughness values, and optical properties of In2O3 thin-films and the electrical characteristics of In2O3 TFTs are studied at different annealing temperatures. Thermal annealing at higher temperature leads to an increase in the saturation mobility (μsat) and a negative shift in the threshold voltage (VTH). The DIW-based processed In2O3-TFT annealed at 300 °C exhibits excellent device performance, and one annealed at 200 °C exhibits an acceptable μsat of 0.86 cm2/V·s comparable to that of a-Si:H TFTs, whereas the 2-ME-based TFT annealed at 300 °C exhibits an abundant μsat of 1.65 cm2/Vs and one annealed at 200 °C is inactive. The results are attributed to the fact that the DIW-based process induces a higher degree of oxidation and less defect states than the 2-ME-based process at the same temperature. The DIW-based process for fabricating the In2O3 TFT opens the way for the development of nontoxic, low-cost, and low-temperature oxide electronics.

Stabilizing and scaling up carbon-based perovskite solar cells

Abstract

(Invited) Solution-Processed Nanostructured Electrochromic Materials: Preparation and Application

Electrochromic materials and devices can change color under applied potentials, which are widely studied for applications in energy-saving smart windows, rearview mirrors, displays, and so forth. The operation of electrochromic materials and devices involves the gain or loss of electrons and simultaneous insertion/extraction of ions with opposite charges to balance the internal electric fields. The performance is therefore limited by kinetics of charge transport in electrochromic materials as well as ion migration in electrolytes, materials and at their interfaces. Nanostructured electrochromic materials have an extremely short charge transport distance facilitating charge transport in electrochromic devices and large specific surface area improving the contact with electrolytes, which may result in enhanced electrochromic properties. By using solution-processed technology, we prepared nanostructured electrochromic materials, including hydrothermally synthesized WO3 nanorods, NiO nanosheets, flower-like NiO micro-nanostructures, well-adhesive WO3 and Prussian blue films directly grown on transparent conductive glass, electrodeposited Prussian blue film. Electrochromic devices based on these materials show their potential applications in smart windows, displays and self-rechargeable batteries.

Rational Design: A High-Throughput Computational Screening and Experimental Validation Methodology for Lead-Free and Emergent Hybrid Perovskites

Perovskite solar cells, with efficiencies of 22.1%, are the only solution-processable technology to outperform multicrystalline silicon and thin-film solar cells. Whereas substantial progress has been made in scalability and stability, toxicity concerns drive the need for lead replacement, intensifying research into the broad palette of elemental substitutions, solid solutions, and multidimensional structures. Perovskites have gone from comprising three to more than eight (CH3NH3, HC(NH2)2, Cs, Rb, Pb, Sn, I, Br) organic and inorganic constituents, and a variety of new embodiments including layered, double perovskites, and metal-deficient perovskites are being explored. Although most experimentation is guided by intuition and trial-and-error-based Edisonian approaches, rational strategies underpinned by computational screening and targeted experimental validation are emerging. In addressing emergent perovskites, this perspective discusses the rational design methodology leveraging density functional theor...

Toward Lead-Free Perovskite Solar Cells

Since the first reports of solar cells with power conversion efficiencies around 10% in 2012, the science and technology of perovskite photovoltaics has been progressing at an unprecedented rate. The current certified record efficiency of 22.1% makes perovskites the first solution-processable technology to outperform multicrystalline and thin-film silicon. For this technology to be deployed on a large scale, the two main challenges that need to be addressed are the material stability and the toxicity of lead. In particular, while lead is allowed in photovoltaic modules, it would be desirable to find alternatives which retain the unique optoelectronic properties of lead halide perovskites. Here we offer our perspective on the most exciting developments in the materials science of new halide perovskites, with an emphasis on alternatives to lead. After surveying recent developments of new perovskites and perovskite-related materials, we highlight the potential of halide double perovskites. This new family of...

Nondilute 1,2-dichloroethane solution of poly(9,9-dioctylfluorene-2,7-diyl): A study on the aggregation process

Molecular aggregates in conjugated polymer (CP) solution can propagate into mesoscale morphology of the relevant film and further dominate the optoelectronic property. Herein, we probed the aggregation behavior of poly(9,9- dioctylfluorene-2,7-diyl) (PFO) and studied its influence on the photophysical property in 1,2-dichloroethane (DCE) solution, where the contents of β-phase or -aggregates increased with prolonged aging time. Thereinto, high quality β-film was fabricated from DCE solution with critical aggregate time of 6 min. The film exhibited excellent surface morphology and characteristic emission of β-phase. Meanwhile, films prepared from aged DCE solutions exhibited high crystallinity, which was promising to obtain higher photoluminance efficiency and charge transport ability simultaneously. Therefore, it is significant to get deep insight into the aggregation behavior of CP, which is involved not only with the solution-processing technology of plastic device, but also with the optoelectronic property of CP.

A bipolar macrospirocyclic oligomer based on triphenylamine and 4,5-diazafluorene as a solution-processable host for blue phosphorescent organic light-emitting diodes

A bipolar macrospirocyclic trimer based on 4,5-diazafluorene and triphenylamine was prepared as a host for solution-processed blue phosphorescent organic light emitting diodes. The oligomer exhibits a high triplet energy of 2.88 eV, excellent thermal and morphological stability, good film-forming ability and solution processability. A solution-processed phosphorescent device based on FIrpic and the trimer achieved a maximum current efficiency of 10.0 cd A−1 with a low current efficiency roll-off at the practical luminance (9.6, 10.0, 9.4 cd A−1 at 102, 207, 1096 cd m−2, respectively). The oligomer additionally showed excellent chemical compatibility with the common host for solution-processing technology. A blue phosphorescent device using mixed hosts of the trimer/4,4′-cyclohexylidenebis(N,N-bis(4-methyl -phenyl)benzenamine) achieved a low turn-on voltage of 3.0 V, a maximum luminance of 28,368 cd m−2, and a maximum current efficiency of 17.7 cd A−1 (11.9 lm W−1), which is almost three times that of a single 4,4′-cyclohexylidenebis(N,N- bis(4-methylphenyl)benzenamine)-hosted device.