Organic−Inorganic Nanocomposites via Directly Grafting Conjugated Polymers onto Quantum Dots

Novel pyrene-pyridine oligomer nanorods for super-sensitive fluorescent detection of Pd2

Conjugated polymers (CPs) can be fabricated into conjugated polymer nanoparticles of various shapes, thus tuning the hydrophobicity and sensing performances of the parent polymers. Herein, two new hydrophobic oligomeric CPs containing pyrene-pyridyl moieties, P1 and P2, were directly prepared and conveniently converted into hydrophilic nanorods, i.e. P1NRs and P2NRs (about 4-21 and 6-20 nm in diameter), by a modified microemulsion method. Notably, separated P1NRs exhibit excellent stability while P2NRs tend to stack on each other perhaps due to their different rigidity of π-delocalized backbones, which may have a profound effect on their fluorescence properties. In addition, Pd²⁺ can coordinate with the pyridyl N atoms, thereby causing ultrasensitive fluorescence quenching of P1NRs and P2NRs owing to the aggregation of oligomeric CP nanorods. These two simple nanosensors can help to determine Pd²⁺ with detection limits as low as 1 and 70 nM, respectively. It is worth noting that biocompatible P1NRs with bright blue fluorescence can be employed for efficient imaging of trace level Pd²⁺ ions in live cells.

Binary Self-Assembly of Conjugated Block Copolymers and Quantum Dots at the Air-Liquid Interface into Ordered Functional Nanoarrays

Controlling the nanoscale morphology of conducting polymer/nanoparticle hybrid films is a highly desired but challenging task. Here, we report that such functional hybrid films with unprecedented structural order can be formed through the self-assembly of conjugated block copolymers and CdSe quantum dots at the air-water interface. The one-step assembly of quantum dots and block copolymers composed of polythiophene and polyethylene glycol (P3HT-b-PEG) at the fluidic interface generated a highly ordered assembly structure of P3HT nanowires and one-dimensional quantum dot arrays. Structure analyses revealed a unique self-assembly behavior and size dependency, which are distinct from the conventional self-assembly of coil-type polymers on solid substrates. Interestingly, hydrophobic quantum dots reside at the interface between P3HT and PEG domains without disrupting the P3HT packing structure, which is advantageous for the optoelectronic properties. Furthermore, large particles bridge the P3HT nanowires at both ends, while small particles decorate each P3HT/PEG interfaces, thus forming tight p-n junctions for a broad size range of nanoparticles. The nanoparticle-incorporated hybrid films showed more than an order of magnitude higher photocurrent and light sensitivity compared to polymer-only films, consistent with the assembly structure with close contact between the organic and inorganic semiconductors.

Characterizing Polymer-Grafted Nanoparticles: From Basic Defining Parameters to Behavior in Solvents and Self-Assembled Structures

Polymer-grafted nanoparticles, often called hairy nanoparticles (HNPs), are an intriguing class of nanostructured hybrid materials with great potential in a variety of applications, including advanced polymer nanocomposite fabrication, drug delivery, imaging, and lubrication. This Feature provides an introduction to characterization of various aspects of HNPs, from basic defining parameters to behavior of HNPs in solvents and self-assembled structures of multicomponent brush nanoparticles, by using a broad range of analytical tools.

End-Functionalized Semiconducting Polymers as Reagents in the Synthesis of Hybrid II-VI Nanoparticles

The functionalization of II-VI nanocrystals with semiconducting polymers is of fundamental interest for lightweight, solution-processed optoelectronics. The direct surface functionalization of nanocrystals is useful for facilitating charge transfer across the donor/acceptor interface, in addition to promoting good mixing properties and thereby helping prevent nanoparticle aggregation. In this work, we develop a new method for the direct attachment of semiconducting polymers to II-VI inorganic nanocrystals, where the polymer plays a dual role, acting as both the desired capping agent and a chalcogenide monomer during synthesis. The success of this hybridization procedure relies on the establishment of a new polymer end-functionalization scheme, where a route toward a thio-phosphonate polymer end-group is developed; this end-group resembles many chalcogenide precursor materials used in the synthesis of II-VI nanomaterials. We show the applicability of this hybrid functionalization procedure by attaching poly(3-hexylthiophene-2,5-diyl) to CdSe and CdS. We followed the progress of the reaction by NMR and used transmission electron microscopy to determine the morphology of the resulting materials, which we found to have narrow size distributions after hybridization. Polymer attachment to the nanocrystals was confirmed by examining the steady-state and time-resolved optical properties of the hybrid materials, which also provided an insight into excited-state processes occurring across the hybrid interface.

Interface Engineering Strategies for Fabricating Nanocrystal-Based Organic–Inorganic Nanocomposites

Hybrid organic–inorganic nanocomposites have attracted considerable attention because they have the advantages of both conjugated polymers (CPs) and nanocrystals (NCs). Recent developments in the interfacial engineering of CP–NC organic–inorganic nanocomposites enabled the formation of an intimate contact between NCs and CPs, facilitating electronic interactions between these two constituents. To design CP–NC nanocomposites, several approaches have been introduced, including ligand refluxing, direct grafting methods, direct growth of NCs in proximity to CPs, and template-guided strategies. In this review, the general reactions of ligand exchange processes, purification methods, and characterization techniques have been briefly introduced. This is followed by a highlight of recent advances in the synthesis of hybrid CP–NC nanocomposites and newly developed inorganic surface treatments, as well as their applications. An outlook for future directions in this area is also presented.

Quantum dot-polymer conjugates for stable luminescent displays

The broad absorption of light in the UV-Vis-NIR region and the size-based tunable photoluminescence color of semiconductor quantum dots make these tiny crystals one of the most attractive antennae in solar cells and phosphors in electrooptical devices. One of the primary requirements for such real-world applications of quantum dots is their stable and uniform distribution in optically transparent matrices. In this work, we prepare transparent thin films of polymer-quantum dot conjugates, where CdSe/ZnS quantum dots are uniformly distributed at high densities in a chitosan-polystyrene copolymer (CS-g-PS) matrix. Here, quantum dots in an aqueous solution are conjugated to the copolymer by a phase transfer reaction. With the stable conjugation of quantum dots to the copolymer, we prevent undesired phase separation between the two and aggregation of quantum dots. Furthermore, the conjugate allows us to prepare transparent thin films in which quantum dots are uniformly distributed at high densities. The CS-g-PS copolymer helps us in not only preserving the photoluminescence properties of quantum dots in the film but also rendering excellent photostability to quantum dots at the ensemble and single particle levels, making the conjugate a promising material for photoluminescence-based devices.

Assembly of P3HT/CdSe nanowire networks in an insulating polymer host

Nanoparticles may act as compatibilizing agents for blending of immiscible polymers, leading to changes in blend morphology through a variety of mechanisms including interfacial adsorption, aggregation, and nucleation of polymer crystals. Herein, we report an approach to define highly structured donor/acceptor networks based on poly(3-hexylthiophene) (P3HT) and CdSe quantum dots (QDs) by demixing from an insulating polystyrene (PS) matrix. The incorporation of QDs led to laterally phase-separated co-continuous structures with sub-micrometer dimensions, and promoted crystallization of P3HT, yielding highly interconnected P3HT/QD hybrid nanowires embedded in the polymer matrix. These nanohybrid materials formed by controlling phase separation, interfacial activity, and crystallization within ternary donor/acceptor/insulator blends, offer attractive morphologies for potential use in optoelectronics.

Microstructure Formation of Functional Polymers by Evaporative Self-Assembly under Flexible Geometric Confinement

Polymer microstructures are widely used in optics, flexible electronics, and so forth. We demonstrate a cost-effective bottom-up manner for patterning polymer microstructures by evaporative self-assembly under a flexible geometric confinement at a high temperature. Two-parallel-plates confinement would become curve-to-flat shape geometric confinement as the polydimethylsiloxane (PDMS) cover plate deformed during solvent swelling. We found that a flexible cover plate would be favorable for the formation of gradient microstructures, with various periodicities and widths obtained at varied heights of clearance. After thermal annealing, the edge of the PMMA (Poly-methylmethacrylate) microstructures would become smooth, while the RR-P3HT (regioregular-poly(3-hexylthiophene)) might generate nanocrystals. The morphologies of RR-P3HT structures included thick films, straight lines, hierarchical stripes, incomplete stripes, and regular dots. Finally, a simple field-effect transistor (FET) device was demonstrated with the RR-P3HT micropattern as an active layer.

Self-Assembled Core-Shell CdTe/Poly(3-hexylthiophene) Nanoensembles as Novel Donor-Acceptor Light-Harvesting Systems

The self-assembly of novel core-shell nanoensembles consisting of regioregular poly(3-hexylthiophene) nanoparticles (P3HT_NPs) of 100 nm as core and semiconducting CdTe quantum dots (CdTe_QDs) as shell with a thickness of a few tens of nanometers was accomplished by employing a reprecipitation approach. The structure, morphology, and composition of CdTe_QDs/P3HT_NPs nanoensembles were confirmed by high-resolution scanning transmission microscopy and dynamic light-scattering studies. Intimate interface contact between the CdTe_QDs shell and the P3HT_NPs core leads to the stabilization of the CdTe_QDs/P3HT_NPs nanoensemble as probed by the steady-state absorption spectroscopy. Effective quenching of the characteristic photoluminescence of CdTe_QDs at 555 nm, accompanied by simultaneous increase in emission of P3HT_NPs at 660 and 720 nm, reveals photoinduced charge-transfer processes. Probing the redox properties of films of CdTe_QDs/P3HT_NPs further proves the formation of a stabilized core-shell system in the solid state. Photoelectrochemical assays on CdTe_QDs/P3HT_NPs films show a reversible on-off photoresponse at a bias voltage of +0.8 V with a 3 times increased photocurrent compared to CdTe_QDs. The improved charge separation is directly related to the unique core-shell configuration, in which the outer CdTe_QDs shell forces the P3HT_NPs core to effectively act as electron acceptor. The creation of novel donor-acceptor core-shell hybrid materials via self-assembly is transferable to other types of conjugated polymers and semiconducting nanoparticles. This work, therefore, opens new pathways for the design of improved optoelectronic devices.

Photoluminescence Quenching and Enhanced Optical Conductivity of P3HT-Derived Ho(3+)-Doped ZnO Nanostructures

In this article, we demonstrate the surface effect and optoelectronic properties of holmium (Ho(3+))-doped ZnO in P3HT polymer nanocomposite. We incorporated ZnO:Ho(3+) (0.5 mol% Ho) nanostructures in the pristine P3HT-conjugated polymer and systematically studied the effect of the nanostructures on the optical characteristics. Detailed UV-Vis spectroscopy analysis revealed enhanced absorption coefficient and optical conductivity in the P3HT-ZnO:Ho(3+) film as compared to the pristine P3HT. Moreover, the obtained photoluminescence (PL) results established the improvement of exciton dissociation as a result of ZnO:Ho(3+) nanostructures inclusion. The occurrence of PL quenching is the result of enhanced charge transfer due to ZnO:Ho(3+) nanostructures in the polymer, whereas energy transfer from ZnO:Ho(3+) to P3HT was verified. Overall, the current investigation revealed a systematic tailoring of the optoelectronic properties of pristine P3HT after inclusion of ZnO:Ho(3+) nanostructures, thus opening brilliant perspectives for applications in various optoelectronic devices.

Intimate organic-inorganic nanocomposites via rationally designed conjugated polymer-grafted precursors

Semiconducting organic-inorganic nanocomposites comprising the conjugated polymer poly(3-hexylthiophene) (P3HT) in intimate contact with CdSe nanocrystals were crafted by exploiting rationally designed P3HT-grafted cadmium precursors (i.e., Cd-P3HT complexes). The bifunctional ligand 4-bromobenzyl phosphonic acid (BPA-Br) that possesses two terminal functional groups at each end was employed, enabling the coordination of BPA-Br with Cd first to yield Cd-phosphonic acid complexes (Cd-BPA-Br) followed by the subsequent substitution of the bromide moiety into the azide (N3) group to form N3-functionalized Cd-phosphonic acid complexes (Cd-BPA-N3). Cd-P3HT complexes were then synthesized via a click reaction between Cd-BPA-N3 and ethynyl-terminated P3HT (P3HT-[triple bond, length as m-dash]). The success of the click reaction was confirmed by spectroscopic measurements. The morphology of CdSe nanocrystals (i.e., quantum dot and multi-branched) in P3HT-CdSe nanocrystal nanocomposites can be altered by tuning the concentration of Cd-P3HT complexes and the addition of excess Cd-BPA-Br (i.e., Cd-P3HT solely for the synthesis of CdSe quantum dots, and Cd-P3HT and Cd-BPA-Br at the ratio Cd-P3HT : Cd-BPA-Br = 1 : 1 for the synthesis of multi-branched CdSe nanocrystals). The photophysical properties of the resulting P3HT-CdSe nanocomposites were examined via absorption and photoluminescence studies. In comparison with P3HT-[triple bond, length as m-dash], the significant emission quenching of nanocomposites suggested the efficient charge transfer at the P3HT/CdSe interface. It is noteworthy that the implementation of judiciously synthesized Cd-P3HT complexes as precursors rendered the in situ synthesis of P3HT-CdSe nanocrystal nanocomposites, dispensing with the need for the use of insulating aliphatic ligands and tedious ligand exchange procedures for the preparation of functional polymer-tethered nanocrystals.

t-Bu3P-Coordinated 2-Phenylaniline-Based Palladacycle Complex/ArBr as Robust Initiators for Controlled Pd(0)/t-Bu3P-Catalyzed Suzuki Cross-Coupling Polymerization of AB-Type Monomers

t-Bu₃P-coordinated 2-phenylaniline-based palladacycle complex (1) as the unique source of Pd(0)/t-Bu₃P to form efficient initiators with ArBr for controlled Suzuki cross-coupling polymerizations of AB-type monomers was described. The in situ generated initiators were demonstrated to be robust initiator systems for controlled Suzuki cross-coupling polymerization, affording polymers with unprecedentedly narrow PDIs and well-controlled functional end groups. ³¹P NMR study suggested that the fast and efficient generation of ArPd(t-Bu₃P)Br complexes from precatalyst 1 and ArBr might be the reason for better control of polymerization with precatalyst 1/ArBr as initiators. Our study provided a family of unprecedented, highly efficient initiators for controlled Suzuki cross-coupling polymerizations and a direct route to access conjugated polymers with a variety of heterobisfunctional chain end groups.

Monodisperse Dual-Functional Upconversion Nanoparticles Enabled Near-Infrared Organolead Halide Perovskite Solar Cells

Extending the spectral absorption of organolead halide perovskite solar cells from visible into near-infrared (NIR) range renders the minimization of non-absorption loss of solar photons with improved energy alignment. Herein, we report on, for the first time, a viable strategy of capitalizing on judiciously synthesized monodisperse NaYF4 :Yb/Er upconversion nanoparticles (UCNPs) as the mesoporous electrode for CH3 NH3 PbI3 perovskite solar cells and more importantly confer perovskite solar cells to be operative under NIR light. Uniform NaYF4 :Yb/Er UCNPs are first crafted by employing rationally designed double hydrophilic star-like poly(acrylic acid)-block-poly(ethylene oxide) (PAA-b-PEO) diblock copolymer as nanoreactor, imparting the solubility of UCNPs and the tunability of film porosity during the manufacturing process. The subsequent incorporation of NaYF4 :Yb/Er UCNPs as the mesoporous electrode led to a high efficiency of 17.8 %, which was further increased to 18.1 % upon NIR irradiation. The in situ integration of upconversion materials as functional components of perovskite solar cells offers the expanded flexibility for engineering the device architecture and broadening the solar spectral use.

Trap Engineering of CdTe Nanoparticle for High Gain, Fast Response, and Low Noise P3HT:CdTe Nanocomposite Photodetectors

Cd(2+) causes deep traps on the surface of CdTe quantum dots (QDs) often leading to a long response time for a photodetector. Poly(3-hexylthiophene) (P3HT) can be used to selectively passivate the Cd(2+) -related deep traps by forming a Cd-S bond, while maintaining the shallow traps. By tailoring the trap depth of the CdTe QDs, a high gain, fast response, and low noise P3HT:CdTe nanocomposite photodetector is achieved.

Morphology control in biphasic hybrid systems of semiconducting materials

Simple blends of inorganic nanocrystals and organic (semiconducting) polymers usually lead to macroscopic segregation. Thus, such blends typically exhibit inferior properties than expected. To overcome the problem of segregation, polymer coated nanocrystals (nanocomposites) have been developed. Such nanocomposites are highly miscible within the polymer matrix. In this Review, a summary of synthetic approaches to achieve stable nanocomposites in a semiconducting polymer matrix is presented. Furthermore, a theoretical background as well as an overview concerning morphology control of inorganic NCs in polymer matrices are provided. In addition, the morphologic behavior of highly anisotropic nanoparticles (i.e. liquid crystalline phase formation of nanorod-composites) and branched nanoparticles (spatial orientation of tetrapods) is described. Finally, the morphology requirements for the application of inorganic/organic hybrid systems in light emitting diodes and solar cells are discussed, and potential solutions to achieve the required morphologies are provided.

Synthesis of Conducting Polymer-Metal Nanoparticle Hybrids Exploiting RAFT Polymerization

The direct covalent attachment of conducting polymers (CP) to nanoparticles (NP) to form CP-NP nanohybrids is of great interest for optoelectronic device applications. Hybrids formed by covalently anchoring CP to NP, rather than traditional blending or bilayer approaches, is highly desirable. CP-NP nanohybrids have increased interfacial surface area between the two components, facilitating rapid exciton diffusion at the p-n heterojunction. These materials take advantage of the facile solution processability, lightweight characteristics, flexibility, and mechanical strength associated with CPs, and the broad spectral absorption, photostability, and high charge carrier mobility of NPs. We demonstrate the ability to polymerize a hole transporting (HT) polymer utilizing reversible-addition-fragmentation chain transfer (RAFT) polymerization and its subsequent rapid aminolysis to yield a thiol-terminated HT polymer. Subsequent facile attachment to gold (Au) and silver (Ag) NPs and cadmium selenide (CdSe) quantum dots (QDs), to form a number of CP-NP systems is demonstrated and characterized. CP-NP nanohybrids show broad spectral absorptions ranging from UV through visible to the near IR, and their facile synthesis and purification could allow for large scale industrial applications.

Surface-initiated polymerization of A–A/B–B type conjugated monomers by palladium-catalyzed Stille polycondensation: towards low band gap polymer brushes

A surface-initiated Stille polycondensation from Pd catalyst-immobilized ZnO nanorods affords well-defined core–shell nanoparticles. For the first time, a low band gap polymer was anchored on ZnO nanorods to create hybrid materials with tunable photophysical properties.

Accessing conjugated polymers with precisely controlled heterobisfunctional chain ends via post-polymerization modification of the OTf group and controlled Pd(0)/t-Bu3P-catalyzed Suzuki cross-coupling polymerization

Accessing of conjugated polymers with precisely controlled heterobisfunctional chain ends was achieved via the post-polymerization modification of the triflate (OTf) group.

Conjugated polymer P3HT–Au hybrid nanostructures for enhancing photocatalytic activity

Organic–inorganic hybrid nanostructures for designing new optical based materials for efficient photocatalysis.

Unimolecular micelles composed of inner coil-like blocks and outer rod-like blocks crafted by combination of living polymerization with click chemistry

Star-shaped PS-b-P3HT was synthesized via a combination of ATRP, GRIM polymerization, and click reaction. They possessed different properties as compared to their linear analogues

Polymer-coated quantum dots

Quantum Dots (QDs) are semiconductor nanocrystals with distinct photophysical properties finding applications in biology, biosensing, and optoelectronics. Polymeric coatings of QDs are used primarily to provide long-term colloidal stability to QDs dispersed in solutions and also as a source of additional functional groups used in further chemical derivatization of the nanoparticles. We review the coating methods, including multidentate and amphiphilic polymeric coatings, and grafting-to and grafting-from approaches. We highlight the most commonly used polymers and discuss how their chemical structure influences the coating properties.

The effect of solvatochromism on the interfacial morphology of P3HT-CdS nanowire nanohybrids

Increasing performance in organic/inorganic bulk heterojunctions hybrid photovoltaic systems hinges not only on the structure of the inorganic component but also on the morphology of the polymeric component. Changing the morphology of the organic component is a facile way of changing the morphology of the interface between the inorganic and organic components in the bulk heterojunction system. Engineering this interface to more efficiently split photogenerated excitons and transport these carriers to electrodes can increase the efficiency of photovoltaic devices. In this report, we investigate the effect of solvent quality on the morphology of the poly(3-hexylthiophene)-2,5-diyl (P3HT) polymer-semiconductor interface (solvatochromism). We have found that creating more order within the P3HT main chain in solution and prior to deposition has a profound effect on the nature of the P3HT-CdS nanowire interface. Solvents with a larger difference in solubility parameter, Δδ, relative to P3HT, such as methanol and isopropanol, create larger rod domains in the P3HT main chain and result in larger domains of crystalline P3HT at the interface. Solvents with similar solubility parameters as P3HT, such as pyridine and hexanol, create relatively shorter rod domains in the main chain and, as a result, nanohybrids with reduced crystallinity. The results of this paper further cement the importance of manipulating the rod-coil transition in the conducting polymers such as P3HT to improve the crystallinity at the polymer-semiconductor interface that can easily be scaled up to improve the efficiency of bulk heterojunction photovoltatic systems.

Nanochemistry and nanomaterials for photovoltaics

Nanochemistry and nanomaterials provide numerous opportunities for a new generation of photovoltaics with high solar energy conversion efficiencies at low fabrication cost. Quantum-confined nanomaterials and polymer-inorganic nanocomposites can be tailored to harvest sun light over a broad range of the spectrum, while plasmonic structures offer effective ways to reduce the thickness of light-absorbing layers. Multiple exciton generation, singlet exciton fission, photon down-conversion, and photon up-conversion realized in nanostructures, create significant interest for harvesting underutilized ultraviolet and currently unutilized infrared photons. Nanochemical interface engineering of nanoparticle surfaces and junction-interfaces enable enhanced charge separation and collection. In this review, we survey these recent advances employed to introduce new concepts for improving the solar energy conversion efficiency, and reduce the device fabrication cost in photovoltaic technologies. The review concludes with a summary of contributions already made by nanochemistry. It then describes the challenges and opportunities in photovoltaics where the chemical community can play a vital role.