Conjugated Random Copolymers Consisting of Pyridine- and Thiophene-Capped Diketopyrrolopyrrole as Co-Electron Accepting Units To Enhance both <i>J</i>_SC and <i>V</i>_OC of Polymer Solar Cells

One of the effective strategies to enhance the photovoltaic performance of polymer solar cells (PSCs) is to synthesize random copolymers composed of one electron donating unit and two different electron accepting units, if the absorptions of two electron accepting units are complementary to each other. To this end, we synthesized a new series of conjugated random copolymer composed of bithiophene (electron donating unit) with thiophene-capped diketopyrrolopyrrole (TDPP) and pyridine-capped diketopyrrolopyrrole (PyDPP) (co-electron accepting units). The random copolymers show broad light absorption and face-on orientation on the substrate, which is beneficial to achieving high short circuit current. The open circuit voltage of the random copolymer can also be controlled systematically by varying the ratio of PyDPP to TDPP in the copolymer, since the HOMO energy level becomes deeper as the PyDPP content in the random copolymer is increased. Consequently, the solar cell device made of the random copolymer with the ratio of 3:1 (TDPP:PyDPP) shows higher PCE (8.11%) than those made of corresponding homopolymers, PTDPP2T (6.70%) and PPyDPP2T (4.14%)

Development of Highly Crystalline Donor–Acceptor-Type Random Polymers for High Performance Large-Area Organic Solar Cells

We developed donor–acceptor (D–A)-type random polymers based on 3,3′-difluoro-2,2′-bithiophene with various relative amounts of 5,6-difluoro-4,7-bis­(5-bromo-(2-decyl­tetradecyl)­thiophen-2-yl)-2,1,3-benzothiadiazole (2FBT) and 5,6-difluoro-4,7-bis­(5-bromo-(2-octyldodecyl)­thiophen-2-yl)-2-(3,4-dichloro­benzyloxybutyl)-2<i>H</i>-benzo­[<i>d</i>]­[1,2,3]­triazole (DCB-2FBTZ). Introducing small relative amounts of DCB-2FBTZ into the polymer was found to effectively enhance its solar cell performance, resulting in a power conversion efficiency of 9.02%, greater than the 7.29% that resulted from the PFBT-FTh copolymer. Moreover, when the active area of the BHJ film was increased to 1 cm², the solar cell reproducibly showed a high performance, here with an efficiency of 8.01% even when the thickness of the active layer was 313 nm. Our studies revealed that including the DCB-2FBTZ group in the polymer simultaneously improved the solution processability and crystallinity of the polymer. These improvements resulted in the formation of highly homogeneous BHJ films throughout large areas with only minor amounts of defects resulting from overaggregation and hence with appropriate morphologies for effective charge generation and transport

Anomalistic Self-Assembled Phase Behavior of Block Copolymer Blended with Organic Derivative Depending on Temperature

Amphiphilic Pluronic block copolymers have attracted great attention in a broad spectrum of potential applications due to the excellent phase behaviors in an aqueous solution, and many efforts have been made to investigate their phase behaviors under various external conditions. With a variety of external conditions, however, the closed looplike phase behaviors of a Pluronic block copolymer in an aqueous solution have not been reported yet. Herein, we report the closed looplike (CLL) phase behavior of a Pluronic P65 triblock copolymer blended with an organic derivative, 5-methylsalicylic acid (5mS), in aqueous solution, which is very unique for block copolymers. As the 5mS concentration increases, the isotropic to ordered phase or back to isotropic phase transition temperature is decreased while the number of closed loops is increased to two. To the best of our knowledge, this is the first demonstration of a CLL phase transition of a Pluronic block copolymer in an aqueous solution, which is readily applicable to optical devices such as optical sensors or optoelectronics, and nanotemplates for a highly ordered superlattice. Furthermore, this provides new insight into the understanding on the phase behavior of a Pluronic block copolymer blended with additives

Nanoporous Block Copolymer Membranes for Ultrafiltration: A Simple Approach to Size Tunability

Nanoporous structures were obtained by the self-assembly of polystyrene-<i>b</i>-poly(methyl methacrylate) (PS-<i>b</i>-PMMA) block copolymers (BCP) where, in thick films, cylindrical microdomains were oriented normal to the substrate and air interfaces, and in the interior of the films, the microdomains were randomly oriented. Continuous nanopores that penetrated through the film were readily produced by a simple preferential swelling of the PMMA microdomains. The confined swelling and rapid contraction of PMMA microdomains generated well-defined uniform pores with diameters to 17.5 nm. The size selectivity and rejection of Au nanoparticles (NPs) for these ultrafiltration (UF) membranes were demonstrated, suggesting an efficient route to tunable, noncomponent-degradative UF membranes

Organic Photovoltaics Utilizing a Polymer Nanofiber/Fullerene Interdigitated Bilayer Prepared by Sequential Solution Deposition

Organic photovoltaics (OPVs) utilizing an interdigitated bilayer of an alkoxy­naphthalene-based polymer nanofiber/fullerene have been developed by the sequential solution deposition (SqD) process. Spin-coating a polymer solution incorporated with 1-chloro­naphthalene (1-CN) results in the formation of dense polymer nanofibers with diameters of 30–50 nm. The fullerene top layer is sequentially deposited onto the polymer nanofiber bottom layer to form a bulk heterojunction (BHJ) through the interdiffusion of fullerene. Compared to a plane polymer bottom layer, the preformed polymer nanofiber bottom layer provides effective interdiffusion of phenyl-C₇₁-butyric acid methyl ester (PCBM) by facilitating the fast swelling of the PCBM solvent into the polymer bottom layer. The SqD processed OPV utilizing a polymer nanofiber/fullerene bilayer exhibits higher photocurrent density compared to those utilizing a plane polymer layer/fullerene bilayer. Furthermore, the SqD OPV exhibited superior solar cell performance to the OPV prepared by the polymer:fullerene blend solution deposition (BSD) process. Optical, morphological, and <i>J–V</i> investigations on the photoactive layers reveal that improved ordering of the polymer chain with proper direction and increased heterojunction area are the main contributors to the superior solar cell performance. These results suggest an efficient interdigitated BHJ morphology can be realized by a sequentially deposited, preformed nanofiber/fullerene bilayer without a thermal annealing process

Nanoconfinement-Dependent Chain Orientation of Polymorphs in Poly(3-dodecylthiophene)s

Nanoconfinement of conjugated polymers (CPs) is an effective strategy to control the orientations and orderings of CPs, which determine their electrical properties. We investigate the chain orientations of two crystal polymorphs, Form I and Form II, in poly(3-dodecylthiophene)s (P3DDTs) using a porous anodic aluminum oxide (AAO) template. The control of regioregularity (RR) of P3DDTs results in well-defined Form II/Form I ratios of crystal polymorphs. Interestingly, Form I and Form II crystals show considerably different orientational changes depending on the pore diameter (Dpore) of the porous AAO template. As Dpore decreases from 100 to 30 nm, Form II crystals change their orientations from face-on to edge-on dominant morphologies, whereas Form I crystals consistently exhibit edge-on dominant morphologies. In addition, for a fixed Dpore of 100 nm, temperature-dependent orientational changes of Form I and Form II are investigated. While Form II crystals show a significant orientational change with increasing temperature, Form I crystals only experience chain reconfiguration. This finding provides useful guidelines for achieving the CPs with controlled intermolecular assembly and chain orientations

Substrate-Independent Lamellar Orientation in High-Molecular-Weight Polystyrene‑<i>b</i>‑poly(methyl methacrylate) Films: Neutral Solvent Vapor and Thermal Annealing Effect

Lamellar microdomain orientation in polystyrene-<i>b</i>-poly­(methyl methacrylate) (PS-<i>b</i>-PMMA) films was controlled by a solvent vapor annealing process, where the high-molecular-weight block copolymer (BCP) was used to self-assemble in a large period of 105 nm. A neutral solvent annealing with tetrahydrofuran vapor screened the difference in the surface energy between the two blocks and the interfacial interactions of the substrate with each block, leading to the substrate-independent perpendicular orientation of lamellar microdomains. Together with thermal annealing of the solvent-annealed BCP film, we demonstrate that highly ordered line arrays of perpendicularly oriented lamellae were well guided in topographic line and disk photoresist patterns composed of the PS-attractive cross-linked copolymer, where the interlamellar <i>d</i>-spacing compliant to the patterns was dependent on the confinement types

One-Dimensional Supramolecular Nanoplatforms for Theranostics Based on Co-Assembly of Peptide Amphiphiles

We report a simple and facile strategy for the preparation of multifunctional nanoparticles with programmable properties using self-assembly of precisely designed block amphiphiles in an aqueous solution-state. Versatile, supramolecular nanoplatform for personalized needs, particularly–theranostics, was fabricated by coassembly of peptide amphiphiles (PAs) in aqueous solution, replacing time-consuming and inaccessible chemical synthesis. Fibrils, driven by the assembly of hydrophobic β-sheet–forming peptide block, were utilized as a nanotemplate for drug loading within their robust core. PAs were tagged with octreotide [somatostatin (SST) analogue] for tumor-targeting or were conjugated with paramagnetic metal ion (Gd³⁺)-chelating 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for magnetic resonance (MR) imaging. The two PA types were coassembled to integrate each PA function into original fibrillar nanotemplates. The adoption of a bulky target-specific cyclic octreotide and β-sheet-forming peptide with enhanced hydrophobicity led to a morphological transition from conventional fibrils to helical fibrils. The resulting one-dimensional nanoaggregates allowed the successful intracellular delivery of doxorubicin (DOX) to MCF-7 cancer cells overexpressing SST receptor (SSTR) and MR imaging by enabling high longitudinal (<i>T</i>₁) relaxivity of water protons. Correlation between the structural nature of fibrils formed by PA coassembly and contrast efficacy was elucidated. The coassembly of PAs with desirable functions may thus be a useful strategy for the generation of tailor-made biocompatible nanomaterials

Chemical Doping Effects in Multilayer MoS₂ and Its Application in Complementary Inverter

Multilayer MoS₂ has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS₂ devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly­(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS₂, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 10⁶). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS₂ that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal–oxide–semiconductor inverter that uses a p-type MoSe₂ and a PDPP3T-doped MoS₂ as charging and discharging channels, respectively

<i>Protic</i> Ionic Liquids for Intrinsically Stretchable Conductive Polymers

Inspired by the classic hard–soft acid–base theory and intrigued by a theoretical prediction of spontaneous ion exchange between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and hard-cation–soft-anion ionic liquid (IL), we treat PEDOT:PSS with a new IL composed of a protic (i.e., extremely hard) cation (3-methylimidazolium, p-MIM+) and an extremely soft anion (tetracyanoborate, TCB–). In fact, this protic IL (p-MIM:TCB) accomplishes the same levels of ion-exchange-mediated PEDOT–PSS separation, PEDOT-rich nanofibril formation, and electrical conductivity enhancement (∼2500 S/cm) as its aprotic counterpart (EMIM:TCB with 1-ethyl-3-methylimidazolium), the best IL used for this purpose so far. Furthermore, p-MIM:TCB significantly outperforms EMIM:TCB in terms of improving the stretchability (i.e., the highest tensile strain) of the PEDOT:PSS thin film. This enhancement is a result of the aromatic and protic cation p-MIM+, which acts as a molecular adhesive holding the exchanged ion pairs (PEDOT+:TCB–---p-MIM+:PSS–) via ionic intercalation (at the surface of TCB–-decorated PEDOT+ clusters) and hydrogen bonding (to PSS–), in which washing p-MIM+ out of the film degrades the stretchability while keeping the morphology. Our results offer molecular-level insight into the morphological, electrical, and mechanical properties of PEDOT:PSS and a molecular-interaction-based enhancement strategy that can be used for intrinsically stretchable conductive polymers