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Mechanochromic, tough and healable polyurethane films are synthesized and their properties are thoroughly characterized. The optimum films are utilized to explore the potential applications of shape memory and flexible capacitor devices.

Binary acceptor alloys based on two A′′–D′A′D′–A′′ small molecule acceptors having the same core but different end groups provided OPV with high PCE, Voc and stability.

Multi-responsive and optically-active diarylethene-based [2]pseudo-rotaxane polymers Zn2+-TC2/DS(O & C) were synthesized and prepared via metal–ligand and host–guest interactions, where Zn2+ ion was coordinated with two ligands (TC) containing a macrocyclic dibenzo-24-crown-8 (DB24C8) linked to a terpyridyl terminus to form a symmetrical host (Zn2+-TC2) and diarylethene (DAE) bearing two terminal secondary ammonium salts to form a symmetrical guest (DS). Upon irradiation of UV-light (λ = 355 nm), the prominent photo-induced electron transfer (PET) off process to promote optical-switchable Forster resonance energy transfer (FRET) process from the emissive metal-coordination Zn2+-TC2 host to the fluorescent DS(C) guest (in the closed form of emissive DAE unit) was explored for the multiple-responsive turn-on ratiometric fluorescence in supramolecular polymer Zn2+-TC2/DS(C). Remarkably, endowed with the novel features of reversible chemical/chelation-stimuli responsive dis-assembly/re-assembly of non-covalent interactions in response to pH/chelation, the polymer can be used for the sensing of pH and cyclen. Accordingly, the “molecular wire and stimuli-responsive effects” of diarylethene-based [2]pseudo-rotaxane polymer Zn2+-TC2/DS(C) reveal significant supramolecular interactions to elucidate the turn-on fluorescence via the controllable FRET-ON process from Zn2+-TC2 host donor to PET-OFF DS(C) guest acceptor, which pave a promising route to elaborate optical-switchable supramolecular platforms for the future energy transfer applications.

The fabrication with high energy density and superior electrical/electrochemical properties of hierarchical porous 3D cross-linked graphene-based supercapacitors is one of the most urgent challenges for developing high-power energy supplies. We facilely synthesized a simple, eco-friendly, cost-effective heteroatoms (nitrogen, phosphorus, and fluorine) co-doped graphene oxide (NPFG) reduced by hydrothermal functionalization and freeze-drying approach with high specific surface areas and hierarchical pore structures. The effect of different heteroatoms doping on the energy storage performance of the synthesized reduced graphene oxide is investigated extensively. The electrochemical analysis performed in a three-electrode system via cyclic voltammetry (CV), galvanostatic charging–discharging (GCD), and electrochemical impedance spectroscopy (EIS) demonstrates that the nitrogen, phosphorous, and fluorine co-doped graphene (NPFG-0.3) synthesized with the optimum amount of pentafluoropyridine and phytic acid (PA) exhibits a notably enhanced specific capacitance (319 F g−1 at 0.5 A g−1), good rate capability, short relaxation time constant (τ = 28.4 ms), and higher diffusion coefficient of electrolytic cations (Dk+ = 8.8261 × 10−9 cm2 s−1) in 6 M KOH aqueous electrolyte. The density functional theory (DFT) calculation result indicates that the N, F, and P atomic replacement within the rGO model could increase the energy value (GT) from −673.79 eV to −643.26 eV, demonstrating how the atomic level energy could improve the electrochemical reactivity with the electrolyte. The improved performance of NPFG-0.3 over NFG, PG, and pure rGO is mainly ascribed to the fast-kinetic process owing to the well-balanced electron/ion transport phenomenon. A symmetric coin cell supercapacitor device fabricated using NPFG-0.3 as the anode and cathode material with 6 M KOH aqueous electrolyte exhibits maximum specific energy of 38 W h kg−1, a maximum specific power of 716 W kg−1, and ∼88.2% capacitance retention after 10 000 cycles. The facile synthesis approach and promising electrochemical results suggest this synthesized NPFG-0.3 material has high potential for future supercapacitor application.

This study presents the synthesis of small-molecule acceptors having the structure A–D–A′–D–A—where A, A′, and D represent the end group, the core and π-bridge unit, respectively—that form the active layers with the polymer PM6 for organic photovoltaics. Increasing the number of core perylenetetracarboxylic diimide (PDI) units and conjugating them with thienothiophene (TT) or dithiophenepyrrole (DTP) π-bridge units enhanced the intramolecular charge transfer (ICT) and also increased effective conjugation, thereby, improving the light absorption and molecular packing. The absorption coefficient of hPDI-DTP-IC2F (two PDI with DTP) has the highest value (8 × 104 cm−1) because it featured the greatest degree of ICT, being much larger than that of PDI-TT-IC2F (one PDI with TT), hPDI-TT-IC2F (two PDI with TT) and PDI-DTP-IC2F (one PDI with DTP) (1.64 × 104 cm−1). The PM6:hPDI-DTP-IC2F device provided the highest power conversion efficiency (PCE) of 11.6%; this value was more than twice that of the PM6:PDI-DTP-IC2F (4.8%) device. This large increase in the PCE of the devices from the one-PDI core to two-PDI core case can be attributed to the two-PDI core case having (i) a stronger ICT, (ii) proper molecular packing that provided higher and more balanced carrier mobilities and (iii) a smaller energy loss than for the one-PDI case. Therefore, increasing the number of PDI units that were conjugated with suitable chromophores for stronger ICT in small molecule acceptors can be an effective way for enhancing the efficiency of organic photovoltaics.

We reported a new and environmentally friendly phloroglucinol additive incorporated polyvinyl alcohol–LiClO4 gel polymer electrolyte for flexible symmetrical solid-state supercapacitors. The incorporation of 10 wt% phloroglucinol into PVA–LiClO4 gel polymer electrolytes results in much higher specific capacitance (114 F g−1) than that without phloroglucinol (60 F g−1), an increase of 90%, because of the redox reaction of phloroglucinol in the system. We used the PVA–LiClO4 with 10 wt% phloroglucinol as a gel polymer electrolyte in combination with nitrogen-doped graphene nanosheet-based electrodes as the anode and cathode to fabricate a symmetrical solid-state supercapacitor. The fabricated supercapacitor involving the phloroglucinol redox additive has an energy density of 2.3 W h kg−1 at a power density of 150 W kg−1, which is higher than the one without a redox additive (1.9 W h kg−1 at a power density of 150 W kg−1). Moreover, the supercapacitor involving the redox additive has good stability; its capacitance remains at up to ∼94% after 5000 charge/discharge cycles.

In this paper we report the effect on the power conversion efficiency (PCE) and stability of photovoltaic devices after incorporating hydrogenated two-dimensional (2D) MoSe2 nanosheets into the active layer of bulk heterojunction (BHJ) organic photovoltaics (OPV). The surface properties of 2D MoSe2 nanosheets largely affect their dispersion in the active layer blend and, thus, influence the carrier mobility, PCE, and stability of corresponding devices. We treated MoSe2 nanosheets with hydrogen plasma and investigated their influence on the polymer packing and fullerene domain size of the active layer. For the optimized devices incorporating 37.5 wt% of untreated MoSe2, we obtained a champion PCE of 9.82%, compared with the champion reference PCE of approximately 9%. After incorporating the hydrogen plasma-treated MoSe2 nanosheets, we achieved a champion PCE of 10.44%—a relative increase of 16% over that of the reference device prepared without MoSe2 nanosheets. This PCE is the one of the highest ever reported for OPVs incorporating 2D materials. We attribute this large enhancement to the enhanced exciton generation and dissociation at the MoSe2–fullerene interface and, consequently, the balanced charge carrier mobility. The device incorporating the MoSe2 nanosheets maintained 70% of its initial PCE after heat-treatment at 100 °C for 1 h; in contrast, the PCE of the reference device decreased to 60% of its initial value—a relative increase in stability of 17% after incorporating these nanosheets. We also incorporated MoSe2 nanosheets (both with and without treatment) into a polymer donor (PBDTTBO)/small molecule (IT-4F) acceptor system. The champion PCEs reached 7.85 and 8.13% for the devices incorporating the MoSe2 nanosheets with and without plasma treatment, respectively—relative increases of 8 and 12%, respectively, over that of the reference. These results should encourage a push toward the implementation of transition metal dichalcogenides to enhance the performances of BHJ OPVs.

This paper reports two new fluorine-substituted polymer donors (BO2FC8, BO2FEH), with different side-chain architectures, and a new chlorine-substituted small-molecule acceptor (m-ITIC-OR-4Cl) that are capable of simultaneous charge and energy transfer as the binary blend active layer for organic photovoltaics. We first resolved the single-crystal structure of m-ITIC-OR-4Cl and then used simultaneous grazing-incidence wide- and small-angle X-ray scattering to decipher the multi-length-scale structures—such as the shape and size of aggregated domains and molecular orientation—of the blends of BO2FEH and BO2FC8 with m-ITIC-OR-4Cl. The linear side chains of BO2FC8 facilitated its packing and, thus, induced m-ITIC-OR-4Cl to form smaller disc-shaped aggregated domains (thickness: 2.9 nm) than its aggregate domain (thickness: 5.4 nm) in the blend of the branched BO2FEH. That is, the binary blend system of linear-side-chain BO2FC8 with m-ITIC-OR-4Cl featured larger interfacial areas and more pathways for charge transfer and transport, as evidenced by their carrier mobilities. The highest power conversion efficiency (PCE) of 11.0% was that for the BO2FC8:m-ITIC-OR-4Cl device, being consistent with the predicted PCE of 11.2% using machine learning based on random forest algorism; in comparison, the PCE of the BO2FEH:m-ITIC-OR-4Cl device was 6.4%. This study has not only provided insight into the photovoltaic performances of new polymer donor/small-molecule acceptor blends but has also, for the first time, deciphered the hierarchical morphologies—from molecule orientation to nano-domain shape and size—of such blend systems, linking the morphologies to the photovoltaic performances. The use of side-chain architectures suggests an approach for tuning the morphology of the polymer/small-molecule binary blend active layer for use in organic photovoltaics.

In this paper we report a facile and rapid electrochemical process, involving simultaneous in situ cathodic plasma exfoliation and nitrogen doping, for the production of nitrogen-doped graphene nanosheets. We used a novel electrochemical process to generate the plasma in situ: a graphite rod, serving as a cathode, generated in situ cathodic plasma when it came into slight contact with the electrolyte containing proper nitrogen species that can undergo dissociation with plasma and then form bonds with carbon such as ammonia molecules or nitrate/nitrite anions, resulting in induced exfoliation of the tip of the graphite rod into nitrogen-doped graphene nanosheets. X-ray photoelectron spectroscopy, elemental analysis, and energy-dispersive X-ray spectroscopy revealed that the concentration of nitrogen atoms doped in the graphene nanosheets varied from 0.6 to 0.81 at%. Transmission electron microscopy and scanning electron microscopy revealed that the as-produced nitrogen-doped graphene nanosheets comprised four layers of graphene and had a specific surface area of 164 m2 g−1. This process has potential for use in the industrial-scale mass production of nitrogen-doped graphene for various applications.

A novel photo-switchable polymer P-PHT containing diarylethene (DAE) and tetraphenylethene (TPE) moieties and a triazole linker in the repeating unit was synthesized to study the aggregation-induced emission (AIE) behaviour of TPE with both the open and closed forms of DAE in P-PHT with high water contents. The photo-switching phenomena of DAE (from open to closed forms under UV-irradiation) in P-PHT were prominent in organic solvent (THF), high water contents (at 90% H2O) and acidic conditions. Upon UV-irradiation of P-PHT at 90% water content, the AIE of TPE was completely quenched via an energy transfer event from TPE to cyclized DAE. Interestingly, the rare monomeric emission of TPE was first discovered by the photo-cyclization of DAE in P-PHT compared with the AIE behaviour of TPE with the open form of DAE in P-PHT with AIE favourable conditions of high water content (90% H2O) and acidic conditions.

Over the last ten years, the molecular architectures of p-type donor–acceptor (D–A) conjugated polymers designed for bulk heterojunction (BHJ) photovoltaics, when mixed with fullerenes or n-type polymers, have progressed substantially from one-dimensional (1-D) to branched to two-dimensional (2-D) D–A conjugated structures. In the 1-D structures, alternating D and A units allow internal charge transfer along the conjugated backbone and increase the effective resonance length, as a result of facilitated π-electron delocalization. Upon progressing from 1-D structures to branched D–A conjugated polymers (comprising repeating donor units in the main chain with electron-withdrawing side chain units) to 2-D conjugated polymers (having D–A repeating units on their backbones as well as perpendicular electron-donating groups on their D units), the solubility, effective conjugation length, and photophysical and BHJ photovoltaic properties have all been altered dramatically. The ideal p-type 2-D conjugated D–A polymer for use in BHJ photovoltaic devices should possess a low band gap (to broaden the absorption range), excellent packing characteristics (particularly along the out-of-plane direction, ensuring good carrier transport), and suitable energy levels for efficient electron transfer (to fullerene moieties or n-type polymers). In this review, we discuss the effects of the structural characteristics and optical properties of these conjugated polymers as well as their packing characteristics on the device performances.

In this study, we employed ternary blends capable of energy transfer—a synthesized high-band-gap small molecule (SM-4OMe) comprising benzodithiophene (BDT) and rhodanine units (a molecular structure that was designed for energy transfer), a low-band-gap polymer (PTB7-TH) comprising BDT and thienothiophene units with desired packing orientation, and a fullerene—as active layers for single-junction photovoltaic devices. The light absorption of the small molecule and the polymer was partially complementary, owing to their band gap difference, thereby broadening the absorption spectrum of solar light while maintaining the energy band structures that facilitated energy and charge transfer. The synthesized small molecule SM-4OMe and the PTB7-TH had somewhat similar chemical structures—with the same planar BDT donor units—and thus allowed sufficient mixing between them for energy transfer to take place. The power conversion efficiency of a device incorporating a ternary blend of PTB7-TH:SM-4OMe:PC71BM (0.9 : 0.1 : 1.5, w/w/w) as the active layer, processed with diiodooctane (2 vol%) in chlorobenzene, was 10.4%, which is higher than the value of 8% of the corresponding device incorporating PTB7-TH:PC71BM (1 : 1.5, w/w)—an increase of 30%. We attribute this enhancement to the energy transfer from the high-band-gap small molecule SM-4OMe to the low-band-gap polymer PTB7-TH and to the optimal phase-separated bulk heterojunction morphology that comprises a mean PC71BM cluster size of 6 nm, which is lower than 12 nm for the PTB7-TH and PC71BM binary blends, and slightly better in-plane packing, arising from the inducements of the presence of SM-4OMe. This approach provides a facile and effective way to enhance the power conversion efficiency of single junction organic photovoltaics.

Correction for ‘Twisted-graphene-like perylene diimide with dangling functional chromophores as tunable small-molecule acceptors in binary-blend active layers of organic photovoltaics’ by Yu-Che Lin et al., J. Mater. Chem. A, 2021, 9, 20510–20517, DOI: 10.1039/d1ta05697b.

Block copolymers can self-assemble into ordered structures having feature dimensions on the order of 10 to 100 nm; we took advantage of the different polarities of the blocks of a low-molecular-weight diblock copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO) that interact differentially with small molecules and fullerenes to tune the extent of phase separation in solution-processed small-molecule bulk-heterojunction (SMBHJ) solar cells. We incorporated small amounts of nanostructured PS-b-PEO to solar cells' active layers featuring 7,7′-{4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2,6-diyl}bis{6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole} (p-DTS(FBTTh2)2) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) for optimizing the morphology and thus enhancing the devices' power conversion efficiency. For understanding the effect of PS-b-PEO on the devices' performances, we used synchrotron grazing-incidence wide-angle X-ray scattering, atomic force microscopy and transmission electron microscopy to probe and to decipher the morphologies of the resulting SMBHJ thin films. Without undergoing any annealing process, a device with an active layer of p-DTS(FBTTh2)2:PC71BM (1.5 : 1, w/w) that incorporated 0.5 wt% of PS-b-PEO and was processed with a 1,8-diiodooctane solvent additive displayed a power conversion efficiency (PCE) of 7.3%, a relative increase of 2.5 times as compared to the PCE of 2.1% for the control device featuring only p-DTS(FBTTh2)2 and PC71BM. Thus, incorporating this nanostructured block copolymer in the active layer allowed effective tuning of the small molecule active layer morphology and resulted in enhanced device efficiency.

This study reports the electrochemical performance of pseudosupercapacitor electrodes composed of cubic phase Co3O4 nanoparticles, reduced graphene oxide (rGO) and functionalized MWCNTs based nanocomposites. The Co3O4/rGO/CNTs nanocomposites have been synthesized using a hydrothermal method and the EPD technique has been used to make binder free electrodes of the nanocomposite materials for supercapacitor applications. The effects of graphene oxide (GO) concentration and the ratio of GO/CNTs on the electrochemical performance of the nanocomposite material have been investigated. From the experimental results, the Co3O4/rGO/CNTs nanocomposite synthesized with 2 mg mL−1 GO concentration and 10 : 1 GO/CNT ratio exhibits a good specific capacitance of 850 F g−1 at a 5 mV s−1 scan rate and 790 F g−1 at 1 A g−1, excellent rate capability and good cyclability in 1 M KOH. Furthermore, we have successfully designed an aqueous electrolyte-based asymmetric pseudocapacitor using Co3O4/rGO/CNTs nanocomposite as an anode and N-doped graphene nanocomposite as a cathode. The operating voltage of our optimized asymmetric pseudocapacitor is 1.4 V and it exhibits the maximum energy density and power density of 19.6 W h kg−1 and 7250 W kg−1, respectively. These results suggest that our EPD grown nanocomposite binder free electrode and our designed asymmetric pseudocapacitor have a good potential for practical applications.

Two new ladder-type conjugated polymers, PIDTT-DFBT-EH and PIDTT-F-PhanQ-EH, are prepared through the copolymerization of heptacyclic IDTT with F-PhanQ and DFBT electron deficient moieties. The introduction of 4-(2-ethylhexyloxy)-phenyl (EHOPh) side-chains onto the polymer is beneficial for achieving high molecular weight and good solution-processability of materials. The derived polymer solar cells yielded PCEs of 5.48% (PIDTT-DFBT-EH) and 5.14% (PIDTT-F-PhanQ-EH), without engaging post-solvent or solvent additive treatments.

In this study we synthesized a series of solution-processable small molecules comprising 2,2′-bithiophene (BTh), terthiophene (TTh), and thiobarbituric acid (TB) units as the central core, π-conjugated spacer, and acceptor end-capping moieties, respectively, but with alkyl side-chains of different lengths presented from their central BTh units (TBTThBTh-H, TBTThBTh-C4, TBTThBTh-C8, TBTThBTh-C12). We then investigated the structure–property relationships of these compounds in terms of their packing behaviors and bulk heterojunction (BHJ) photovoltaic properties. And we found that the packing of these molecules in neat films is critically dependent of their side-chain lengths, as evidenced by the variations in their lamellar structures determined with grazing-incidence wide-angle X-ray scattering (GIWAXS). The power conversion efficiencies (PCEs) of the photovoltaic BHJ devices comprising these small molecules and PC61BM exhibited zigzag-shaped variations with respect to the alkyl side-chain lengths, with the PCE of devices incorporating TBTThBTh-H and TBTThBTh-C8 being higher than those of devices incorporating TBTThBTh-C4 and TBTThBTh-C12. Using GIWAXS to probe the molecular packing in the BHJ active layers, we found that the alkyl chain lengths of the small molecules had a large impact on the formation of crystallites in the BHJ films; the molecules with more uniform and shorter alkyl side-chain lengths provide stronger intermolecular interactions, being more favorable for the crystallization of these molecules.

The spatial arrangement of metal nanoparticle (NP) arrays in block copolymers has many potential applications in OFET-type memory devices. In this study, we adopted a trapping approach in which we used a monolayer thin film of polystyrene-block-poly(4-vinylpyridine) (PS56k-b-P4VP8k)-a highly asymmetric diblock copolymer having a spherical micelle morphology-to incorporate various amounts of one-phase-synthesized dodecanethiol-passivated silver (DT-Ag) NPs and a fixed amount of ligand-exchanged pyridine-coated gold (Py-Au) NPs into the polystyrene (PS) and poly(4-vinylpyridine) (P4VP) blocks, respectively. We characterized the packing of these metal NPs in the two blocks of the nanostructured diblock copolymer using reciprocal-space synchrotron grazing incidence small-angle X-ray scattering (GISAXS) as well as atomic force microscopy (AFM) and transmission electron microscopy (TEM) in the real space. The packing of the Ag NPs in the PS block was dependent on their content, which we tuned by varying the concentrations in the composite solution at a constant rate of spin-coating. The two-dimensional hierarchical arrangement of Ag and Au NPs within the BCP thin films was enhanced after addition of the Py-Au NPs into the P4VP block and after spin-coating a thinner film from a low concentration solution (0.1 wt%), due to the DT-Ag NPs accumulating around the Py-Au/P4VP cores; this two-dimensional hierarchical arrangement decreased at a critical DT-Ag NP weight ratio (c) of 0.8 when incorporating the Py-Au NPs into the P4VP domains through spin-coating at higher solution concentration (0.5 wt%), where the DT-Ag NPs realigned by rotating 20° along the z axis in the real space, due to oversaturation of the DT-Ag NPs within the PS domains.

Three series of supramolecular mono-(i.e., Ru1G1, Ru1G2 and Ru1G3), bis-(i.e., BTRu2G1, BTRu2G2 and BTRu2G3) and tris-(i.e., TPARu3G1, TPARu3G2 and TPARu3G3) Ru-based dendritic complexes were synthesized. Their photophysical and electrochemical properties were investigated. These metallodendritic complexes covered a broad absorption range of 250–750 nm with optical bandgaps of 1.51– 1.86 eV. The energy levels of the metallo-dendrimers can be effectively adjusted not only by different generations of dendritic thiophene arms but also by their p-conjugated core ligands bearing various electron donor (i.e., triphenylamine) and acceptor (i.e., benzothiadiazole) moieties. Due to the donor– acceptor effect, the bis-Ru-based dendrimers containing a benzothiadiazole electron-acceptor core ligand showed the highest power conversion efficiency (PCE) among these three series of metallodendrimers. The tris-Ru-based architecture with a triphenylamine electron-donor core ligand revealed moderate photovoltaic performance. Among the different generations (G1–G3) of dendrimers, the third generation (G3) possessed the highest PCE values in each series of Ru-based dendrimers. Hence, the third generation bis-‘Ru’-based dendrimer BTRu2G3 blended with PC70BM (1 : 3 w/w) showed the highest PCE value of 0.77% (without the aid of additives or annealing), which is the highest efficiency among all bulk hetero-junction (BHJ) solar cells containing metallo-dendrimers reported to date.

We demonstrate an efficient method for the production of few-layer MoS2 nanosheets through exfoliation of bulk MoS2 compounds that were subject to quenching in liquid N2 and subsequent ultrasonication. This solution-based method, which involves a “quenching cracks” phenomenon, was performed open to the atmosphere. Subsequent ultrasonication of the exfoliated MoS2 in solution provided us with MoS2 nanosheets comprising two to four layers.

A novel platinum complex PtC with a tri-armed uracil hydrogen-bonded (H-bonded) unit was synthesized via a modular synthetic approach and characterized by 1H, 13C NMR and MALDI-TOF mass spectroscopies. Two H-bonded tetrads, PtC–(TPAD1)3 and PtC–(TPAD2)3, based on a metal core PtC complexed with two generations of triarylamine dendrimers, TPAD1 and TPAD2 (with electron-donating nature), were successfully constructed with improved organic solubility via a classical H-bonded self-assembly approach. Supramolecular H-bonding in solution and solid state was elucidated by 1H NMR titrations, IR spectral studies and time resolved photoluminescence (TRPL) measurements. The electron/energy transfers, as well as the self-assemblies of supramolecular tetrads, were established by UV-Vis and PL titrations and AFM morphological studies. Furthermore, metal complex core PtC showed selective sensitivity towards Ag+ ions through fluorescence turn-off responses without any interference from other common metal ions. The 1 : 1 binding stoichiometry and complexation mechanism between the probe and Ag+ ion was established by 1H NMR titration. Moreover, PL reversibility of PtC + Ag+ could be achieved on addition of PMDTA.

In this study we synthesized the donor–acceptor conjugated copolymers PBTT4BT and PBTT4BO featuring benzotrithiophene (BTT) units as donors and benzothiadiazole (BT) and benzoxadiazole (BO) units, respectively, as acceptors, linked through 4-dodecylthiophene spacers. The presence of the spacer units enhanced not only the solubility of the synthesized polymers but also their molecular packing in the solid state; both of these polymers exhibited good crystallinity, as evidenced by a d-spacing of 23.8 A in the (100) plane in their X-ray diffraction curves. When we used these synthesized polymers in bulk heterojunction photovoltaic device applications, the optimal device incorporating PBTT4BO/PC61BM as the active layer exhibited a low efficiency of 3.2%, due to the poor solubility of PBTT4BO, whereas the optimal device incorporating the more-soluble PBTT4BT and PC71BM displayed an efficiency of 4.4%, which is substantially 1.5% higher than that for the PBTTBT/PC71BM device, where PBTTBT was formed by copolymerizing BTT and BT units without any spacer. After thermal annealing, the efficiency of the PBTT4BT/PC71BM device improved further to 5.6%, with a VOC value of 0.72 V, a JSC value of 11.58 mA cm−2 and a fill factor of 67%. The annealed PBTT4BT/PC71BM active layer possessed a nanoscaled network-like morphology with rod-like PBTT4BT domains that were beneficial for charge separation and transport; accordingly, the power conversion efficiency of the annealed PBTT4BT/PC71BM photovoltaic device was enhanced greatly over that of the as-cast PBTT4BT/PC71BM device.

In this study, we fabricated p-channel-type non-volatile organic field-effect transistor (OFET) memory devices featuring an asymmetric PS-b-P4VP diblock copolymer layer incorporating high- and low-work-function metal nanoparticles (NPs) in the hydrophilic and hydrophobic blocks, respectively. We chose the highly asymmetric diblock copolymer PS56k-b-P4VP8k as the polymer electret to create the memory windows, and used the different work functions of the ex situ-synthesized metal NPs to tune the memory window for either p- or n-channel applications. The transfer curves of non-volatile OFET memory devices incorporating an asymmetric PS56k-b-P4VP8k layer embedded with high-work-function Pt NPs (5.65 eV) in the P4VP block exhibited a positive threshold voltage shift and a large memory window (ca. 27 V). In contrast, the transfer curves of the corresponding non-volatile OFET memory devices featuring embedded low-work-function (4.26 eV) Ag NPs exhibited a negative threshold voltage shift and a smaller memory window (ca. 19 V). This approach provides a versatile way to fabricate p- or possibly n-channel-type non-volatile organic field-effect transistor (OFET) memory devices with the same processing procedure.

In this paper we report a simple and effective approach towards improving the performance of molecular bulk heterojunction (BHJ) photovoltaics through incorporation of a new, nonvolatile processing additive; (3-chloropropyl)trimethoxysilane (CP3MS). A small amount of the additive CP3MS combined with post-annealing treatment significantly enhanced the power conversion efficiency (PCE) of dialkylated diketopyrrolopyrrole chromophore (SMDPPEH)-based molecular BHJ solar cells. The PCE increased from 2.75% for a device prepared without the additive or annealing to 4.55% for a device containing 0.1% CP3MS that had been subjected to post-annealing treatment at 100 °C for 10 min. CP3MS performed an interesting dual function when incorporated as an additive in molecular BHJ devices. The first was that it controlled the morphology: the addition of 0.1% CP3MS to the SMDPPEH:PC61BM blend was sufficient to improve the film's crystallinity and morphology. The second function was the spontaneous migration of the CP3MS molecules from the bulk to the interface between the active layer and the Al cathode, forming an ultrathin interlayer that acted as a buffer layer suppressing charge recombination and enhancing charge transport at the interface. Analyses using atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, together with examinations of device performance, confirmed the dual-functional nature of CP3MS as an additive. CP3MS also showed its promising ability to enhance the performance of different blend systems. The performance of benzodithiophene (BDT)-based molecular solar cells enhanced from 3.05% without additive to 3.8% with the incorporation of 0.1% CP3MS.

We describe a new and highly efficient plasma-assisted electrochemical exfoliation method, involving a plasma-generated graphite cathode and a graphite anode, for the production of graphene sheets from electrodes in a basic electrolyte solution in a short reaction time.

Organic field-effect transistor (OFET) memory devices incorporating the copolymer polystyrene-block-poly(4-vinylpyridine) (PS56k-b-P4VP8k) layer, which features a thickness-dependent micellar nanostructure (P4VP-core, PS-shell), as a charge trapping layer can exhibit tunable memory windows for p-channel applications. For instance, the memory window increased substantially from 7.8 V for the device incorporating a 60 nm thick PS56k-b-P4VP8k layer to 21 V for the device incorporating a 27 nm thick layer, an increase of more than 2.5 times. Using simultaneous synchrotron grazing-incidence small-angle X-ray scattering and wide-angle X-ray scattering to probe the nanostructured micellar PS56k-b-P4VP8k layer and the pentacene layer positioned directly on the top of the copolymer layers, respectively, we were able to elucidate the structural characteristics of the bilayer and to correlate their effects with the memory performances of devices with similar architectures. For the PS56k-b-P4VP8k layers, we found that the inter-micelle distance and their lateral arrangements depended on the layer thickness: the thickness of the PS shells in the lateral direction decreased upon increasing the layer thickness, as did the memory window for the OFET device that incorporated the PS56k-b-P4VP8k layers, showing a strong dependence of the threshold voltage shifts (i.e., memory window) on the distance between the micelles. Additionally, for the molecular packing of the pentacene layer positioned on the copolymer layer, we found that the PS56k-b-P4VP8k layers affected not only the orientation of the pentacene molecules but also their grain sizes, thereby affecting the hole mobility of the memory devices. These results suggest that tuning the micellar nanostructure of the block copolymer thin film that was used as a trapping layer can be a simple and effective way for optimizing the memory window and affecting the hole mobility of OFET memory devices.

We have used Stille coupling polymerization to synthesize a series of new donor–acceptor (D–A) conjugated random copolymers—PBDTT-BO-DPP—that comprise electron-rich alkylthienyl-substituted benzodithiophene (BDTT) units in conjugation with electron-deficient 2,1,3-benzooxadiazole (BO) and diketopyrrolopyrrole (DPP) moieties that have complementary light absorption behavior. These polymers exhibited excellent thermal stability with thermal degrading temperatures higher than 340 °C. Each of these copolymers exhibited (i) broad visible light absorption from 400 to 900 nm and (ii) a low optical band gap that is smaller than 1.4 eV and a low-lying highest occupied molecular orbital that is deeper than −5.22 eV. As a result, bulk heterojunction photovoltaic devices derived from these polymers and fullerenes provided a high short-circuit current density that is larger than 12 mA cm−2. In particular, a photovoltaic device prepared from the PBDTT-BO-DPP (molar ratio, 1 : 0.5 : 0.5)/PC71BM (w/w, 1 : 2) blend system with 1-chloronaphthalene (1 volume%) as an additive exhibited excellent photovoltaic performance, with a value of Voc of 0.73 V, a high short-circuit current density of 17 mA cm−2, a fill factor of 0.55, and a promising power conversion efficiency of 6.8%, indicating that complementary light-absorption random polymer structures have great potential for increasing the photocurrent in bulk heterojunction photovoltaic devices.

Molecular engineering of conjugated polymers for tuning their energy bands is an important process in the quest for highly efficient bulk heterojunction (BHJ) polymer photovoltaic devices. One effective approach is to construct a conjugated polymer by conjugating two chemical units possessing different electron donating (donor) and accepting (acceptor) capabilities. Conjugated copolymers featuring donor–acceptor (D/A) subunits are promising materials for solar cell applications because of their tunable energy bands and solubility that can be tailored to the performances of the photovoltaic devices. Under proper processing conditions, the conjugated polymers with rigid and planar D/A segments can undergo self-assembly to form crystalline structures that improve charge carrier mobility and provide better resistance to the permeation of water and oxygen compared to amorphous polymers. Conjugated polymers with D/A structure have been investigated thoroughly over the last few years. In this highlight, we present an overview of recent developments in BHJ organic photovoltaics employing D/A crystalline copolymers as active layer materials for photon-to-electron conversion, with particular emphasis on crystalline D/A polymers featuring newly developed acceptor structures, including thieno[3,4-c]pyrrole-4,6-dione, diketo-pyrrole-pyrrole, bithiazole, thiazolothiazole and thieno[3,2-b]thiophene moieties, and conclude with future perspectives.

In this study we used convergent syntheses to prepare two novel acceptor–donor–acceptor (A–D–A) small molecules (BT4OT, BT6OT), each containing an electron-rich benzotrithiophene (BT) unit as the core, flanked by octylthiophene units, and end-capped with electron-deficient cyanoacetate units. The number of octylthiophene units affected the optical, electrochemical, morphological, and photovoltaic properties of BT4OT and BT6OT. Moreover, BT4OT and BT6OT possess low-energy highest occupied molecular orbitals (HOMOs), providing them with good air stability and their bulk heterojunction (BHJ) photovoltaic devices with high open-circuit voltages (Voc). A solar cell device containing BT6OT and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in a 1:0.75 ratio (w/w) exhibited a power conversion efficiency (PCE) of 3.61% with a short-circuit current density (Jsc) of 7.39 mA cm−2, a value of Voc of 0.88 V, and a fill factor (FF) of 56.9%. After adding 0.25 vol% of 1-chloronaphthalene (CN) as a processing additive during the formation of the blend film of BT6OT:PC71BM (1:0.75, w/w), the PCE increased significantly to 5.05% with values of Jsc of 9.94 mA cm−2, Voc of 0.86 V, and FF of 59.1% as a result of suppressed nanophase molecular aggregation.

The production of graphite oxide from graphite usually requires strong oxidants, concentrated acids, and a reaction time of the order of 100 h. In this study, we adopted a highly efficient cathodic plasma (CP) process in which the vapor plasma envelope calorific effect provides instant oxidation and expansion of graphite for producing plasma-expanded graphite oxides (PEGOs) from recycled graphite electrodes (GEs) or high purity graphite (HG), within a reaction time of 10 min without the need for strong oxidants or concentrated acids. X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the dramatic structural change from GEs or HG to graphite oxides after the CP process. Furthermore, scanning electron microscopy and transmission electron microscopy revealed that the graphite oxide possessed a spheroidal morphology, with dimensions of 1–3 μm, as a result of melting and subsequent quenching during the plasma electrolysis process. We obtained a stable, homogeneous dispersion of PEGOs in N-methyl-2-pyrrolidone after sonication and filtering of the centrifuged PEGOs. We used these spheroidal graphite oxide particles as effective adsorbents for the removal of pollutants (e.g., Methylene Blue) from aqueous solutions. These PEGOs also served as good precursors for the preparation of graphite nanoplatelets. CP processing appears to be an effective and environmentally friendly means for mass-producing graphite oxide.

We have prepared photovoltaic devices based on blend films of CdSe tetrapods and the donor/acceptor conjugated polymer PDTTTPD, which comprises 2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene and thieno[3,4-c]pyrrole-4,6-dione units. The AM1.5 power conversion efficiency (PCE) of a photovoltaic device containing a PDTTTPD/CdSe tetrapod blend (1 : 9, w/w) that had experienced thermal annealing (130 °C, 20 min) was three times greater than that of the corresponding device incorporating the as-prepared PDTTTPD/CdSe tetrapod blend (2.9% vs. 1.0%). Synchrotron X-ray reflectivity revealed that annealing (i.e., removal of pyridine ligands from the surfaces of the CdSe tetrapods) caused the thickness of the PDTTTPD/CdSe tetrapod blend film to decrease (and its average density to increase) relative to that of the as-prepared blend film. Transmission electron microscopy and atomic force microscopy revealed that thermal annealing enhanced the degree of aggregation of the CdSe tetrapods and induced denser morphologies, leading to substantially increased charge transport, which enhanced the PCE of the device.

In this study, we found that the formation of a p–i–n junction through in situ electrochemical doping is a promising way to enhance the performance of polymer photovoltaic devices. We applied a pre-bias to metal triflate [LiOTf, KOTf, Ca(OTf)2, Zn(OTf)2]/poly(ethylene oxide) (PEO)–incorporated poly[5-(2′-ethylhexyloxy)-2-methoxy-1,4-phenylenevinylene] (MEH-PPV)/{6}-1-(3-(methoxycarbonyl)propyl)-{5}-1-phenyl-[5,6]-C61 (PCBM) photovoltaic devices to form p–i–n junctions in their active layers. Auger depth profile analyses and alternating-current capacitance analyses of these doped devices revealed that the positive and negative ions were distributed unequally to form an asymmetrical p–i–n structure in a thin layer of ca. 100 nm of the polymer, and the intrinsic layer became thinner when formed under a higher pre-bias voltage. Atomic force microscopy and transmission electron microscopy revealed that the addition of metal triflate/PEO to MEH-PPV/PCBM improved the morphology of the composite films. Among the various doped devices, the MEH-PPV/PCBM device incorporating a LiOTf/PEO mixture exhibited the highest power conversion efficiency, a 40% increase relative to that of the reference device (MEH-PPV/PCBM).

We have prepared thin films of PbSe quantum dots (QDs) featuring three different ligands, oleic acid (OA), butylamine (BA), and 1,2-ethanedithiol (EDT), which have pronounced affects on the arrangement and photovoltaic performance of the PbSe QDs in the thin films. Transmission electron microscopy revealed that ligands that altered the inter-QD spacing induced significant changes in the packing of the PbSe QDs in localized regions of small areas (300 × 300 nm) of the thin films: from a superlattice of OA-capped PbSe QDs to a chaotic pattern of EDT-capped PbSe QDs. Using a synchrotron X-ray reflectivity probe and data fitting, we determined that the roughness decreased and the average densities increased for large-area (1.5 × 1.5 cm) PbSe QD thin films capped with BA and EDT, relative to those of the OA-capped PbSe QD film. In particular, the PbSe QDs' vertical packing density, which is critical for charge transport, increased substantially for the system incorporating EDT ligands. As a result, devices containing the EDT-treated PbSe QD film as the active layer displayed much improved power conversion efficiencies (PCEs) relative to those of corresponding devices featuring either the OA- or BA-capped PbSe QD films as active layers. Adopting a layer-by-layer technique, we fabricated a EDT-capped PbSe QD device that exhibited a PCE of 2.45%.

Contrast variation of neutron and X-ray reflections has been adapted to reveal the film in-depth (vertical) composition profiles of the blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) for bulk heterojunction thin-film solar cells, with a PCBM/P3HT weight ratio of c = 0.6, 0.8 and 1.0. The X-ray scattering-length-density (SLD) profiles, extracted from X-ray reflectivity for the blend films spun-cast on Si wafer, exhibit a stratified film morphology of ca. 85 nm film thickness; the corresponding neutron SLD profiles extracted for the same films further elucidate a PCBM-enriched interfacial layer adjacent to the Si substrate. In contrast to the often assumed two-phase model, a three-phase model with porosity included as the third phase has to be used in deducing the absolute volume fractions of PCBM and P3HT from the complementary neutron and X-ray SLD profiles. In general, the thus deduced in-depth composition profiles for the blend films comprise a substantial surface layer (10–15 nm) of ca. 40% porosity, a 50 nm main layer with relatively uniform PCBM–P3HT composition, and a PCBM-enriched interface layer (∼20 nm) with ∼15% porosity. Formation of the surface porosity is related to interfacial instability occurred in a transient surface layer upon film drying. Annealing at 150 °C influences modestly the vertical phase separation of the film, but drastically activates local phase separation for formation and growth of PCBM and P3HT nanodomains, as revealed by grazing incidence small/wide angle X-ray scattering. The surface/interface porosity features (overlooked in nearly all the previous studies) and the composition-dependent vertical phase separation bear hints in advancing device performance via interfacial morphology optimization.