Nanosphere templated continuous PEDOT:PSS films with low percolation threshold for application in efficient polymer solar cells

Fabrication of hierarchical Ru/PEDOT:PSS/Ti3C2Tx nanocomposites as electrochemical sensing platforms for highly sensitive Sudan I detection in food

In our paper, a promising electrochemical sensing platform was fabricated with titanium carbide (Ti₃C₂T_x), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and ruthenium nanoparticles (RuNPs). First, the Shandong pancake structural PEDOT:PSS/Ti₃C₂T_x was prepared by physical stirring. PEDOT:PSS as the dispersant was embedded into the Ti₃C₂T_x nanosheets, increasing the degree of dispersion of the Ti₃C₂T_x nanosheets and further improving the specific surface area of the composite material. Then, RuNPs were supported on the surface of PEDOT:PSS/Ti₃C₂T_x to form the hierarchical ternary nanocomposite of Ru/PEDOT:PSS/Ti₃C₂T_x. The prepared Ru/PEDOT:PSS/Ti₃C₂T_x nanocomposite exhibited promising electrochemical sensing properties toward Sudan I detection with a wide detection range of 0.01 ∼ 100 μM and a high sensitivity of 482.43 μA mM^-1 cm^-2. Moreover, the Ru/PEDOT:PSS/Ti₃C₂T_x sensing platform has been successfully applied for Sudan I detection in ketchup and chili paste, implying the promising application prospect of Ru/PEDOT:PSS/Ti₃C₂T_x in food safety testing.

Breaking of lattice potential well-induced confinement of carriers in conjugated polymers

Recent experimental research has reported that a surface electric field on the polymer solar cell can restrain the recombination of the resultant charged carriers [23]. Based on this, this article reveals an underlying mechanism: If a surface electric field below 4.5 × 10⁴ V/cm is applied to the polymer layer, the electric field drives the charged polaron to transport. Once the polaron approaches and collides with the exciton, it is easily trapped by the potential well produced by the exciton and then forms a charged exciton. The decay of the resultant charged exciton rapidly reduces the number of excitons. However, once the external field surpasses the threshold value of 4.5 × 10⁴ V/cm, the charged polaron absorbs momentum from the external electric field and shakes off the trapping of the exciton. It finally steps out of the original lattice potential well, where the appropriate electric field magnitude ranges from 5.5 × 10⁴ V/cm to 8 × 10⁵ V/cm. After a collision of 300 fs, apart from a phase shift, the exciton still exists. Then, the originally carriers is dissociated when the electric field reaches 0.8 MV/cm. The applied surface field is able to effectively keep the excitons from fusion with the transporting charged polarons, which provides a valid and easily manufactured approach to yield higher efficiency of polymer solar cells.

Synthesis and Thermoelectric Properties of Selenium Nanoparticles Coated with PEDOT:PSS

We synthesized a hybrid nanocomposite comprised of selenium nanoparticles coated with a thin layer of a conductive polymer, poly(3,4-ethylenedioxythiophene), and studied its thermoelectric properties. The conductive polymer layer on the surface of nanoparticles in the composites formed a percolating network running between the stacked nanoparticles, exhibiting an electrical conductivity close to or higher than that of pure polymer. The thermoelectric power factor of the resulting composite was higher than that of individual polymer or selenium nanoparticles. We further increased the electrical conductivity of the composite by thermal annealing, thereby improving the power factor to 15 μW/cmK² which is nine times higher than that of the polymer.

Rapid solvo-microwave annealing for optimizing ordered nanostructures and crystallization of regioregular polythiophene-based block copolymers

Solvo-microwave annealing is an effective method for producing thin films of polythiophene-based block copolymers with ordered structures and high crystallinity in a very short processing time (∼3 min).

Nanoparticle synthesis via bubbling vapor precursors in bulk liquids

Conventional methods for preparing polymer nanoparticles and organic-inorganic composite nanoparticles use solution based top-down processes with surfactants and mechanical stirring. Examples of such processes include emulsion polymerization of monomers to produce polymer nanoparticles and sol-gel reactions involving hydrolysis of inorganic precursors to produce inorganic materials (such as silica and titanium nanoparticles). Here, we show that vaporized precursors of various compounds can be used as reactants to produce polymer, inorganic, and composite nanoparticles. The bubbling action of precursor vapor in a reactant vessel provides a constant supply of precursor species while aiding their rapid mixing in the bulk solution liquid. The vaporization and bubbling processes require only small amounts of energy to prepare nanoparticles or core-shell nanoparticles without forming unwanted side products. Compared to other available techniques, this approach enables precise control of nanoparticle size and shell thickness as functions of vapor supply time and temperature without surfactants. Our approach can potentially be applied to fabricate functional nanomaterials using organic and inorganic precursors for medical, electrical, optical, magnetic and/or catalytic applications.

Solution-Assembled Blends of Regioregularity-Controlled Polythiophenes for Coexistence of Mechanical Resilience and Electronic Performance

Considering all the potential applications of organic electronics in portable, wearable, and implantable devices, it is of great importance to develop electroactive materials that possess mechanical reliability along with excellent electronic performance. The coexistence of these two attributes, however, is very difficult to achieve because there is an inverse relationship between the electrical properties and the mechanical flexibility, both of which are associated with the conjugation length and intermolecular ordering of the polymers. Herein, we demonstrate a simple and robust approach based on solution assembly of two different poly(3-hexylthiophene)s (P3HTs) with regioregularity (RR) contents of 97% and 66% to impart both electrical and mechanical properties to films for organic electronic applications. The 97% RR P3HT exhibits high electronic performance but poor mechanical resilience, and vice versa for the 66% RR P3HT. Selective crystallization of high RR P3HT induced by solution assembly allows the use of a one-step process to construct percolated networks of high RR P3HT nanowires (NWs) in a low RR P3HT matrix. Only 5 wt % of high RR P3HT NWs in a 95 wt % low RR P3HT matrix was required to produce hole mobilities comparable to that of pure high RR P3HT, and this blend film exhibited improvements by factors of 20 and 60 in elongation at break and toughness, respectively. Selective self-assembly of RR-controlled polymers allowed us to overcome the fragile nature of highly crystalline conjugated polymer films without sacrificing their electronic properties.

Gold nanoparticle-polymer nanocomposites synthesized by room temperature atmospheric pressure plasma and their potential for fuel cell electrocatalytic application

Conductive polymers have been increasingly used as fuel cell catalyst support due to their electrical conductivity, large surface areas and stability. The incorporation of metal nanoparticles into a polymer matrix can effectively increase the specific surface area of these materials and hence improve the catalytic efficiency. In this work, a nanoparticle loaded conductive polymer nanocomposite was obtained by a one-step synthesis approach based on room temperature direct current plasma-liquid interaction. Gold nanoparticles were directly synthesized from HAuCl₄ precursor in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The resulting AuNPs/PEDOT:PSS nanocomposites were subsequently characterized under a practical alkaline direct ethanol fuel cell operation condition for its potential application as an electrocatalyst. Results show that AuNPs sizes within the PEDOT:PSS matrix are dependent on the plasma treatment time and precursor concentration, which in turn affect the nanocomposites electrical conductivity and their catalytic performance. Under certain synthesis conditions, unique nanoscale AuNPs/PEDOT:PSS core-shell structures could also be produced, indicating the interaction at the AuNPs/polymer interface. The enhanced catalytic activity shown by AuNPs/PEDOT:PSS has been attributed to the effective electron transfer and reactive species diffusion through the porous polymer network, as well as the synergistic interfacial interaction at the metal/polymer and metal/metal interfaces.

Light Manipulation in Organic Photovoltaics

Organic photovoltaics (OPVs) hold great promise for next-generation photovoltaics in renewable energy because of the potential to realize low-cost mass production via large-area roll-to-roll printing technologies on flexible substrates. To achieve high-efficiency OPVs, one key issue is to overcome the insufficient photon absorption in organic photoactive layers, since their low carrier mobility limits the film thickness for minimized charge recombination loss. To solve the inherent trade-off between photon absorption and charge transport in OPVs, the optical manipulation of light with novel micro/nano-structures has become an increasingly popular strategy to boost the light harvesting efficiency. In this Review, we make an attempt to capture the recent advances in this area. A survey of light trapping schemes implemented to various functional components and interfaces in OPVs is given and discussed from the viewpoint of plasmonic and photonic resonances, addressing the external antireflection coatings, substrate geometry-induced trapping, the role of electrode design in optical enhancement, as well as optically modifying charge extraction and photoactive layers.

Stability of organic solar cells: challenges and strategies

This review highlights the factors limiting the stability of organic solar cells and recent developments in strategies to increase the stability of organic solar cells.

Enhancing mechanical properties of highly efficient polymer solar cells using size-tuned polymer nanoparticles

The low mechanical durability of polymer solar cells (PSCs) has been considered as one of the critical hurdles for their commercialization. We described a facile and powerful strategy for enhancing the mechanical properties of PSCs while maintaining their high power conversion efficiency (PCE) by using monodispersed polystyrene nanoparticles (PS NPs). We prepared highly monodispersed, size-controlled PS NPs (60, 80, and 100 nm), and used them to modify the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) anode buffer layer (ABL). The PS NPs played two important roles; i.e., they served as (1) binders in the PEDOT:PSS films, and (2) interfacial modifiers between ABL and the active layer, resulting in remarkable improvement of the mechanical integrity of the PSCs. The addition of PS NPs enhanced the inherent mechanical toughness of the PEDOT:PSS ABL due to their elastic properties, allowing the modified ABL to tolerate higher mechanical deformations. In addition, the adhesion energy (Gc) between the active layer and the modified PEDOT:PSS layer was enhanced significantly, i.e., by a factor of more than 1.5. The Gc value has a strong relationship with the sizes of the PS NP, showing the greatest enhancement when the largest size PS NPs (100 nm) were used. In addition, PS NPs significantly improve the air-stability of the PSCs by suppressing moisture adsorption and corrosion of the electrodes. Thus, the modification of ABL with PS NPs effectively enhances both the mechanical and the long-term stabilities of the PSCs without sacrificing their PCE values, demonstrating their great potential as applications in flexible organic electronics.

Au@polymer core-shell nanoparticles for simultaneously enhancing efficiency and ambient stability of organic optoelectronic devices

In this paper, we report and discuss our successful synthesis of monodispersed, polystyrene-coated gold core-shell nanoparticles (Au@PS NPs) for use in highly efficient, air-stable, organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). These core-shell NPs retain the dual functions of (1) the plasmonic effect of the Au core and (2) the stability and solvent resistance of the cross-linked PS shell. The monodispersed Au@PS NPs were incorporated into a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film that was located between the ITO substrate and the emitting layer (or active layer) in the devices. The incorporation of the Au@PS NPs provided remarkable improvements in the performances of both OLEDs and OPVs, which benefitted from the plasmonic effect of the Au@PS NPs. The OLED device with the Au@PS NPs achieved an enhancement of the current efficiency that was 42% greater than that of the control device. In addition, the power conversion efficiency was increased from 7.6% to 8.4% in PTB7:PC71BM-based OPVs when the Au@PS NPs were embedded. Direct evidence of the plasmonic effect on optical enhancement of the device was provided by near-field scanning optical microscopy measurements. More importantly, the Au@PS NPs induced a remarkable and simultaneous improvement in the stabilities of the OLED and OPV devices by reducing the acidic and hygroscopic properties of the PEDOT:PSS layer.

Aspect-Ratio Effect of Nanorod Compatibilizers in Conducting Polymer Blends

Nanoparticles (NPs) at the interface between two different polymer blends or fluid mixtures can function as compatibilizers, thereby dramatically improving the interfacial properties of the blends or the fluid mixtures. Their compatibilizing ability is strongly dependent on their size, shape, and aspect ratios (ARs), which determines their adsorption energy to the interface as well as their entropic penalty when they are being strongly segregated at the interface. Herein, we investigated the effect of the ARs of nanorod surfactants on the conducting polymer blend of poly(triphenylamine) (PTPA) templated by polystyrene (PS) colloids. The lengths of the polymer-coated CuPt nanorods (CuPt NRs) were 5, 15, and 32 nm with a fixed width of 5 nm, thus producing three different AR values of 1, 3, and 6, respectively. For quantitative analysis, the morphological and electrical behaviors of the polymer blends were investigated in terms of the volume fraction and AR of the NRs. The dramatic change in the morphological and electrical properties of the blend film was observed for all three NR surfactants at the NR volume fraction of approximately 1 vol %. Therefore, NR surfactants with larger ARs had better compatibilizing power for a given number of NRs in the blends. Also, they exhibited a stronger tendency to be aligned parallel to the PS/PTPA interface. Also, we demonstrated the successful use of the NR surfactants in the fabrication of conducting polymer blend film that requires only minimal concentrations of conducting polymers. To the best of our knowledge, this is the first report of an experiment on the AR effect of NR compatibilizers in polymer blends.

Effect of fullerene tris-adducts on the photovoltaic performance of P3HT:fullerene ternary blends

Fullerene tris-adducts have the potential of achieving high open-circuit voltages (V(OC)) in bulk heterojunction (BHJ) polymer solar cells (PSCs), because their lowest unoccupied molecular orbital (LUMO) level is higher than those of fullerene mono- and bis-adducts. However, no successful examples of the use of fullerene tris-adducts as electron acceptors have been reported. Herein, we developed a ternary-blend approach for the use of fullerene tris-adducts to fully exploit the merit of their high LUMO level. The compound o-xylenyl C60 tris-adduct (OXCTA) was used as a ternary acceptor in the model system of poly(3-hexylthiophene) (P3HT) as the electron donor and the two soluble fullerene acceptors of OXCTA and fullerene monoadduct (o-xylenyl C60 monoadduct (OXCMA), phenyl C61-butyric acid methyl ester (PCBM), or indene-C60 monoadduct (ICMA)). To explore the effect of OXCTA in ternary-blend PSC devices, the photovoltaic behavior of the device was investigated in terms of the weight fraction of OXCTA (W(OXCTA)). When W(OXCTA) is small (<0.3), OXCTA can generate a synergistic bridging effect between P3HT and the fullerene monoadduct, leading to simultaneous enhancement in both V(OC) and short-circuit current (J(SC)). For example, the ternary PSC devices of P3HT:(OXCMA:OXCTA) with W(OXCTA) of 0.1 and 0.3 exhibited power-conversion efficiencies (PCEs) of 3.91% and 3.96%, respectively, which were significantly higher than the 3.61% provided by the P3HT:OXCMA device. Interestingly, for W(OXCTA) > 0.7, both V(OC) and PCE of the ternary-blend PSCs exhibited nonlinear compositional dependence on W(OXCTA). We noted that the nonlinear compositional trend of P3HT:(OXCMA:OXCTA) was significantly different from that of P3HT:(OXCMA:o-xylenyl C60 bis-adduct (OXCBA)) ternary-blend PSC devices. The fundamental reasons for the differences between the photovoltaic trends of the two different ternary-blend systems were investigated systemically by comparing their optical, electrical, and morphological properties.

Efficient light trapping in inverted polymer solar cells by a randomly nanostructured electrode using monodispersed polymer nanoparticles

The randomly nanotextured back electrode provides a simple and efficient route for enhancing photocurrent in polymer solar cells (PSCs) by light trapping, which can increase light absorption within a finite thickness of the active layer. In this study, we incorporated mono-disperse 60 nm polystyrene nanoparticles (PS NPs) into a 50 nm thick poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) anode buffer layer (ABL) to create a randomly nanotextured back electrode with 10 nm height variations in inverted-type PSCs. The roughened interface between the PS NP-PEDOT:PSS ABL and the Ag electrode scatters light in the visible range, leading to efficient light trapping within the device and enhanced light absorption in the active layer. Inverted PSCs with randomly nanotextured electrodes (φ(NP) = 0.31) showed short-circuit current density (J(SC)) and power conversion efficiency (PCE) values that were 15% higher than those of control devices with flat electrodes. External quantum efficiency, reflectance, and optical light scattering as a function of ϕ(NP) were examined to determine the origin of the enhancement in J(SC) and PCE.