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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.

Semi-transparent organic photovoltaics (OPVs) are an emerging solar-energy-harvesting technology with promising applications, such as rooftop energy supplies for environmentally friendly greenhouses. However, the poor operational stability of OPVs poses challenges to their feasibility as incessantly serving facilities. Here we report a reductive interlayer structure for semi-transparent OPVs that improves the operational stability of OPVs under continuous solar radiation. The interlayer effectively suppresses the generation of radicals from the electron transport layer under sunlight and prevents the structural decomposition of the organic photoactive layer during operation. The defects that serve as the charge carrier recombination sites are nullified by the electron-donating functional groups of the reduced molecules, which improves photovoltaic performance. The semi-transparent OPVs demonstrate a power conversion efficiency of 13.5% and an average visible transmittance of 21.5%, with remarkable operational stability (84.8% retention after 1,008 h) under continuous illumination. Greenhouse results show that the semi-transparent OPV roof benefits the survival rate and growth of the crops, indicating the importance of our approach in addressing food and energy challenges.

High-performance porous 3D graphene-based supercapacitors are one of the most promising and challenging directions for future energy technologies. Microporous graphene has been synthesized by the pyrolysis method. The fabricated lightweight graphene with a few layers (FLG) has an ultra-high surface area of 2266 m2 g−1 along with various-sized micropores. The defect-induced morphology and pore size distribution of the fabricated graphene are examined, and the results show that the micropores vary from 0.85 to 1.9 nm and the 1.02 nm pores contribute 30% of the total surface area. The electrochemical behaviour of the electrode fabricated using this graphene has been studied with various concentrations of the KOH electrolyte. The highest specific capacitance of the graphene electrode of 540 F g−1 (close to the theoretical value, ∼550 F g−1) can be achieved by using the 1 M KOH electrolyte. This high specific capacitance contribution involves the counter ion adsorption, co-ion desorption, and ion permutation mechanisms. The formation of a Helmholtz layer, as well as the diffusion of the electrolyte ions, confirms this phenomenon. The symmetrical solid-state supercapacitor fabricated with the graphene electrodes and PVA–KOH gel as the electrolyte exhibits excellent energy and power densities of 18 W h kg−1 and 10.2 kW kg−1, respectively. This supercapacitor also shows a superior 100% coulombic efficiency after 6000 cycles.

A chitosan composite with a vertical array of pore channels is fabricated via an electrophoretic deposition (EPD) technique. The composite consists of chitosan and polyethylene glycol, as well as nanoparticles of silver oxide and silver. The formation of hydrogen bubbles during EPD renders a localized increase of hydroxyl ions that engenders the precipitation of chitosan. In addition, chemical interactions among the constituents facilitate the establishment of vertical channels occupied by hydrogen bubbles that leads to the unique honeycomb-like microstructure; a composite with a porosity of 84%, channel diameter of 488 µm, and channel length of 2 mm. The chitosan composite demonstrates an impressive water uptake of 2100% and a two-stage slow release of silver. In mass transport analysis, both Disperse Red 13 and ZnO powders show a much enhanced transport rate over that of commercial gauze. Due to its excellent structural integrity and channel independence, the chitosan composite is evaluated in a passive suction mode for an adhesive force of 9.8 N (0.56 N cm

In this study, we synthesized four new A-DA'D-A acceptors (where A and D represent acceptor and donor chemical units) incorporating perylene diimide units (A') as their core structures and presenting various modes of halogenation and substitution of the functional groups at their end groups (A). In these acceptors, by fusing dithiophenepyrrole (DTP) moieties (D) to the helical perylene diimide dimer (hPDI) to form fused-hPDI (FhPDI) cores, we could increase the D/A' oscillator strength in the cores and, thus, the intensity of intramolecular charge transfer (ICT), thereby enhancing the intensity of the absorption bands. With four different end group units─IC2F, IC2Cl, IO2F, and IO2Cl─tested, each of these acceptor molecules exhibited different optical characteristics. Among all of these systems, the organic photovoltaic device incorporating the polymer PCE10 blended with the acceptor FhPDI-IC2F (1:1.1 wt %) had the highest power conversion efficiency (PCE) of 9.0%; the optimal PCEs of PCE10:FhPDI-IO2F, PCE10:FhPDI-IO2Cl, and PCE10:FhPDI-IC2Cl (1:1.1 wt %) devices were 5.2, 4.7, and 7.7%, respectively. The relatively high PCE of the PCE10:FhPDI-IC2F device resulted primarily from the higher absorption coefficients of the FhPDI-IC2F acceptor, lower energy loss, and more efficient charge transfer; the FhPDI-IC2F system experienced a lower degree of geminate recombination─as a result of improved delocalization of π-electrons along the acceptor unit─relative to that of the other three acceptors systems. Thus, altering the end groups of multichromophoric PDI units can increase the PCEs of devices incorporating PDI-derived materials and might also be a new pathway for the creation of other valuable fused-ring derivatives.

In this paper, a universal approach toward constructing a new bilayer device architecture, a few-nanometer-thick third-component layer on a bulk-heterojunction (BHJ) binary blend layer, has been demonstrated in two different state-of-the-art organic photovoltaic (OPV) systems. Through a careful selection of a third component, the power conversion efficiency (PCE) of the device based on PM6/Y6/layered PTQ10 layered third-component structure was 16.8%, being higher than those of corresponding devices incorporating the PM6/Y6/PTQ10 BHJ ternary blend (16.1%) and the PM6/Y6 BHJ binary blend (15.5%). Also, the device featuring PM7/Y1-4F/layered PTQ10 layered third-component structure gave a PCE of 15.2%, which is higher than the PCEs of the devices incorporating the PM7/Y1-4F/PTQ10 BHJ ternary blend and the PM7/Y1-4F BHJ binary blend (14.2 and 14.0%, respectively). These enhancements in PCE based on layered third-component structure can be attributed to improvements in the charge separation and charge collection abilities. This simple concept of the layered third-component structure appears to have great promise for achieving high-performance OPVs.

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.

Summary Shallow defects are mostly benign in covalent semiconductors, such as silicon, given that they do not constitute non-radiative recombination sites. In contrast, the existence of shallow defects in ionic perovskite crystals might have significant repercussions on the long-term stability of perovskite solar cells (PSCs) because of the metastability of the ubiquitous formamidinium lead triiodide (FAPbI3) perovskite and the migration of charged point defects. Here, we show that shallow iodine interstitial defects ( I i ) can be generated unintentionally during commonly used post-fabrication treatments, which can lower the cubic-to-hexagonal transformation barrier of FAPbI3-based perovskites to accelerate its phase degradation. We demonstrate that concurrently avoiding the generation of I i and the more effective passivation of iodine vacancies ( V I ) can improve the thermodynamic stability of the films and operational stability of the PSCs. Our most stable PSC retained 92.1 % of its initial performance after nearly 1,000 h of continuous illumination operational stability testing.

Areca palm leaves derived porous carbon material as the electrode for symmetrical solid-state supercapacitors (SSCs). The areca palm leaves biomass was processed using a fast carbonization method followed by in situ chemical activation. The structures and compositions of these biomass-derived carbon materials were characterized using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. One of the biomass-derived porous carbon materials, AR2, was a lightweight carbon material that possessed a large surface area of 876 m2 g–1. Electrochemical studies revealed that AR2 possessed a high specific capacitance of 262 F g–1 at a scan rate of 5 mV s–1. We fabricated symmetrical SSCs featuring these carbon material as major (80 wt%) components of the electrodes and poly(vinyl alcohol)–Li2SO4 as gel polymer electrolyte. The optimal supercapacitor (SAR2) involving AR2 exhibited a specific capacitance of 132 F g–1 at a current density of 0.5 A g–1 and an energy density of 10.3 W h kg–1 at a power density of 375 W kg–1, and durability of retaining 92% of its initial capacitance after 5000 cycles—performance that is the excellent values reported for devices featuring derived from biomass.

We synthesized three conjugated polymers involving sulfur (S)-inserted and chlorine (Cl)-substituted side chains of the parent two-dimensional conjugated polymer—poly(benzodithiophene–thiophene–ben...

In this study, the effect of oxygen vacancy in the CoMn2O4 on pseudocapacitive characteristics was examined, and two tetragonal CoMn2O4 spinel compounds with different oxygen vacancy concentrations and morphologies were synthesized by controlling the mixing sequence of the Co and Mn precursors. The mixing sequence was changed; thus, morphologies were changed from spherical nanoparticles to nanoflakes and oxygen vacancies were increased. Electrochemical studies have revealed that tetragonal CoMn2O4 spinels with a higher number of oxygen vacancies exhibit a higher specific capacitance of 1709 F g−1 than those with a lower number of oxygen vacancies, which have a higher specific capacitance of 990 F g−1. Oxygen vacancies create an active site for oxygen ion intercalation. Therefore, oxidation–reduction reactions occur because of the diffusion of oxygen ions at octahedral/tetrahedral crystal edges. The solid-state asymmetric pseudocapacitor exhibits a maximum energy density of 32 Wh-kg−1 and an excellent cyclic stability of nearly 100%.

In the field of organic photovoltaics, a full electron donor (D) and deficient electron acceptor (A) are used to prepare fragments of conjugated polymers called D–A-type polymers, the efficiency of which is fundamentally affected by the substituents. In this study, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed to elucidate the effects of substituents (methoxy (–OCH3) and fluorine (–F)) on an ethyl 4-(2-ethoxyacetyl)-5-(3-(2-ethylhexyl)-[2,2':5',2''-terthiophen]-5-yl)-2-(4-(2-ethylhexyl)thiophen-2-yl)benzoate polymer. Energy levels, optical absorption, electron–hole distribution, and charge transfer were then calculated on the basis of the optimized structure with different substituents, ranging from monomer to tetramer, and periodic boundary conditions. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels from DFT calculations were in good agreement with the experimental oxidation and reduction potentials. In conclusion, this study demonstrated that –OCH3 helps increase the HOMO energy level and induces a decrease in the band gap; moreover, it can enhance intramolecular charge transfer and the concentration of electrons. The functionalized polymer is suitable for use in the active layer of organic photovoltaics, and functionalization is an effective approach for improving electron transfer.

In this study, we prepared organic photovoltaics (OPVs) featuring an active layer comprising double bulk heterojunction (BHJ) structures, featuring binary blends of a polymer donor and concentration gradients of two small-molecule acceptors. After forming the first BHJ structure by spin-coating, the second BHJ layer was transfer-printed onto the first using polydimethylsiloxane stamps. A specially designed selenium heterocyclic small-molecule acceptor (Y6-Se-4Cl) was employed as the second acceptor in the BHJ. X-ray photoelectron spectroscopy revealed that the two acceptors formed a gradient concentration profile across the active layer, thereby facilitating charge transportation. The best power conversion efficiencies (PCEs) for the double-BHJ-structured devices incorporating PM6:Y6-Se-4Cl/PM6:Y6 and PM6:Y6-Se-4Cl/PM6:IT-4Cl were 16.4 and 15.8%, respectively; these values were higher than those of devices having one-BHJ structures based on PM6:Y6-Se-4Cl (15.0%), PM6:Y6 (15.4%), and PM6:IT-4Cl (11.6%), presumably because of the favorable vertical concentration gradient of the selenium-containing small-molecule Y6-Se-4Cl in the active layer as well as some complementary light absorption. Thus, combining two BHJ structures with a concentration gradient of the two small-molecule acceptors can be an effective approach for enhancing the PCEs of OPVs.

A new universal electron transport layer that involves doping hydrogen-plasma-treated tungsten disulfide (WS2) nanosheets into ZnO for polymer/fullerene or small molecule organic photovoltaics (OPVs) was prepared. A hydrogen plasma treatment was used to alter the structures of WS2 nanosheets such that the W6+ content was converted into W4+; then ZnO:WS2 nanosheets composites were prepared to form electron transport layers (ETLs). The energy band of the ZnO:WS2 films could be tuned from 5.15 to 4.60 eV by varying the concentration of the WS2 nanosheets up to 0.5 wt%. It was found that ZnO:WS2 ETLs exhibited superior charge transport properties than those of the pristine ZnO layer because of the structure changes, as determined from the X-ray scattering characterizations. OPVs incorporating active layers of PTB7-TH/PC71BM and PTB7-TH/IDIC blends exhibited their power conversion efficiencies of 10.3% and 6.7%, respectively, with the incorporation of 0.3 wt% of the WS2 nanosheets, up from 8.9% to 5.4% for the corresponding devices featuring pristine ZnO—relative increases of 16% and 24%, respectively. This study demonstrates the effectiveness of hydrogen plasma treatment for altering the surface structures of two-dimensional transition-metal-dichalcogenide nanosheets, and paves a way for the composite electron transport layers for use in organic photovoltaics.

We prepared the ternary blends active layer by incorporating a new two-dimensional donor-acceptor (D/A) conjugated polymer (BDTTBO) comprising benzo-dithiophene-thiophene-thiophene-benzo oxadiazole chemical units that has three different conjugated side chains bithiophene (BT), benzothiophene (BzT) and thienothiophene (TT) BDTTBO-BT, BDTTBO-BzT and BDTTBO-TT into poly (benzodithiophene-fluorothienothiophene) (PTB7-TH) and PC71BM as for organic photovoltaics (OPVs). We expected that incorporating these BDTTBO with different side chains into the blend of PTB7-TH and PC71BM not only can broaden the absorption of solar spectrum thereby increasing short-circuit current density but also tune the packing of PTB7-TH and the dispersion of PC71BM. In particular, we found that incorporating 10% of BDTTBO-BT to form the PTB7-TH: BDTTBO-BT: PC71BM ternary blend (active layer) device could improve the power conversion efficiency to 10.4% from 9.0% for the binary blend of PTB7-TH: PC71BM device—a relative increase of 15%. We examined the packing orientations of the PBDTTBO: PTB7-TH:PC71BM ternary blend films using synchrotron two-dimensional grazing-incidence wide-angle X-ray scattering, and found that the incorporation of 10% relatively higher crystallinity PBDTTBO-BT, PBDTTBO-BzT or PBDTTBO-TT not only altered the packing orientation of PTB7-TH substantially but also reduced PC71BM cluster size in the ternary blend system, as compared to that in the case of PTB7-TH with PC71BM binary blend, thereby providing more pathways for electrons and thus enhancing the carrier transport in the ternary blend, as evidenced by the carrier mobility.

This paper describes a facile and tunable method, performed at room temperature and amenable to mass-production, for the preparation of nitrogen-doped graphene sheets using in situ electrochemical cathodic plasma exfoliation of a graphite/melamine composite. The plasma generated at the submerged surface of the graphite/melamine composite electrode not only exfoliated the graphite granules into graphene sheets but also induced the doping of nitrogen atoms. The sizes and morphologies of the graphene sheets, comprising four to five layers of graphene, were confirmed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Tuning the concentration of melamine in the graphite/melamine composites led to different levels of nitrogen-doping in the graphene sheets; the stability of the nitrogen-doped graphene sheets was investigated in various harsh environments. Furthermore, the use of the 4.63 at% nitrogen-doped graphene sheets as anode materials resulted in lithium-ion batteries displaying excellent performance, with a capacity of 488 mA h g −1 at 100 mA g−1 after 100 cycles that was better than that of the device incorporating pristine graphene sheets (344 mA h g−1 at 100 mA g−1 after 100 cycles). This method is a new and tunable approach for producing massive amounts of nitrogen-doped graphene sheets from graphite powder at room temperature.

Doping nonmetal atoms into layered transition metal dichalcogenide MX2 structures has emerged as a promising strategy for enhancing their catalytic activities for the hydrogen evolution reaction. In this study, we developed a new and efficient one-step approach that involves simultaneous plasma-induced doping and exfoliating of MX2 bulk into nanosheets–such as MoSe2, WSe2, MoS2, and WS2 nanosheets–within a short time and at a low temperature (ca. 80 °C). Specifically, by utilizing active plasma that is generated with an asymmetric electrical field during the electrochemical reaction at the surface of the submerged cathode tip, we are able to achieve doping of nitrogen atoms, from the electrolytes, into the semiconducting 2H-MX2 structures during their exfoliation process from the bulk states, forming N-doped MX2. We selected N-doped MoS2 nanosheets for demonstrating their catalytic hydrogen evolution potential. We modulated the electronic and transport properties of the MoS2 structure with the synergy of ...

This work reports the synthesis of Au@Cu2O core@shell nanocrystals with controllable shell thicknesses and demonstrates their use as the dual-functional catalyst that can continuously operate under illumination and darkness conditions for efficient E. coli inactivation. On account of the peroxidase mimics of the Au core and Fenton reactivity of the Cu2O shell, the Au@Cu2O nanocrystals exhibit intrinsic peroxidase-like property with the reaction kinetics in accordance with the typical Michaelis–Menten mechanism. On the other hand, time-resolved photoluminescence spectra suggest the prevalence of pronounced charge separation for Au@Cu2O nanocrystals, an important advantage that is favourable for photocatalysis. By combining the photocatalytic capability with the peroxidase mimics features, Au@Cu2O nanocrystals can perform practical photocatalytic decomposition of E. coli under visible light illumination but still show vital activity towards E. coli inactivation after light illumination was turned off. The current study delivers a new catalyst configuration by exploiting the multiple functionalities of nanosized Au and Cu2O for advanced environmental and energy conversion applications.

Summary A tandem structure was invented to enhance photon utilization efficiency and reduce thermal loss. Considering the unique advantages of non-fullerene acceptors (NFAs), the combination of NFAs and the tandem concept shows great potential for organic photovoltaics (OPVs). Herein, a simple strategy to balance the voltage-current trade-off in tandem OPVs by employing mixed NFAs in rear sub-cells is reported. The VOC and JSC of rear sub-cells can be tuned by using the blend of donor/NFA/NFA. This strategy offers an easy approach to balance the VOC and JSC in tandem OPVs toward higher power conversion efficiency (PCE) without rational and careful synthesis of new materials. Tandem OPVs based on mixed NFAs in rear sub-cells exhibited the best PCE of 13.3% in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under asymptotic scans, and a PCE of 11.52% was achieved and recognized on the most recent NREL chart.

Because the visible and the infrared (IR) regions take up ∼47% and ∼51% of the energy in the solar spectrum (AM 1.5G standard), respectively, utilizing the visible light for plant growth and the IR light for power generation is potentially extremely exciting. IR-absorbing organic semiconductors, with localized IR absorption and visible-light transmittance, would be promising materials for this purpose. Here, flexible transparent organic photovoltaics (TOPVs) based on IR-absorbing organic materials were proposed, which can be a simple, low-cost, and promising way to utilize the IR light for electricity generation, and the penetrated visible light will be utilized for photosynthesis in plants. A power-conversion efficiency of ∼10% with an average visible transmittance of 34% was achieved for TOPV devices. Meanwhile, the side-by-side comparison showed that plants grown under the TOPVs filtered light, and those under normal sunlight yielded very similar results. These outcomes demonstrated the results from TOPV devices beyond simple photovoltaic applications.

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.

Postfabrication surface treatment strategies have been instrumental to the stability and performance improvements of halide perovskite photovoltaics in recent years. However, a consensus understanding of the complex reconstruction processes occurring at the surface is still lacking. Here, we combined complementary surface-sensitive and depth-resolved techniques to investigate the mechanistic reconstruction of the perovskite surface at the microscale level. We observed a reconstruction toward a more PbI2-rich top surface induced by the commonly used solvent isopropyl alcohol (IPA). We discuss several implications of this reconstruction on the surface thermodynamics and energetics. Particularly, our observations suggest that IPA assists in the adsorption process of organic ammonium salts to the surface to enhance their defect passivation effects.

In this report, we demonstrated that the incorporation of 15 wt % two-dimensional transition-metal dichalcogenide materials indium selenide (In2Se3) nanosheets into a polymer (PM6)/small molecule (Y6) active layer not only increased its light absorption but also enhanced the long-term stability of the PM6/Y6/In2Se3 ternary blend organic photovoltaic (OPV) devices. The power conversion efficiency (PCE) of the device was improved from 15.7 to 16.5% for the corresponding PM6/Y6 binary blend device. Moreover, the PM6/Y6/In2Se3 device retained 80% of its initial PCE after thermal treatment at 100 °C for 600 h; in comparison, the binary blend device retained only 62% of its initial value. This relative enhancement of 29% resulted from the In2Se3 nanosheets retarding or facilitating molecule packing in different orientations that stabilizes the morphology of the active layer. We adopted a modified kinetics model to account for the intrinsic degradation of the OPV; the degradation-facilitated energy for the degradation kinetics of the PCE for the ternary blend device was 5.3 kJ/mol, half of that (11.3 kJ/mol) of the binary blend device, indicating a slower degradation rate occurring for the case of incorporating In2Se3 nanosheets. Therefore, the incorporation of transition metal dichalcogenide nanosheets having tunable band gaps and large asymmetric shape appears to be a new way to improve the long-term stability of devices and realize the practical use of OPVs.

With the goal of obtaining sustainable earth-abundant electrocatalyst materials displaying high performance in the hydrogen evolution reaction (HER), here we propose a facile one-pot plasma-induced electrochemical process for the fabrication of new core-shell structures of ultrathin MoS

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Selenium (Se) is one of the potential candidates as photodetector because of its outstanding properties such as high photoconductivity (∼8 × 104 S cm–1), piezoelectricity, thermoelectricity, and nonlinear optical responses. Solution phase synthesis becomes an efficient way to produce Se, but a contamination issue that could deteriorate the electric characteristic of Se should be taken into account. In this work, a facile, controllable approach of synthesizing Se nanowires (NWs)/films via a plasma-assisted growth process was demonstrated at the low substrate temperature of 100 °C. The detailed formation mechanisms of nanowires arrays to thin films at different plasma powers were investigated. Moreover, indium (In) layer was used to enhance the adhesive strength with 50% improvement on a SiO2/Si substrate by mechanical interlocking and surface alloying between Se and In layers, indicating great tolerance for mechanical stress for future wearable devices applications. Furthermore, the direct growth of Se NWs...

The three novel acceptor–donor–acceptor (A–D–A) conjugated small molecules were synthesized, each featuring a benzodithiophene (BDT) core presenting lateral flexible side chains: TB-BDT6T substituted with 2-ethynyl-5-octylthiophene, TS-BDT6T substituted with 2-(octylthio)thiophene, and TT-BDT6T substituted with 2-(2-ethylhexyl)thieno[3,2-b]thiophene groups. The lateral incorporation of functionalized π-conjugated flexible side chains, without altering the end-capped acceptor (cyanoacetate) moieties, amended the optoelectronic properties of these BDT-based small molecules. X-ray diffraction spectroscopy revealed that these small molecules possess high crystallinity; moreover, the optimized blend film morphologies, recorded using atomic force microscopy, revealed miscibility with PC61BM, and turn out nanoscale phase separations. The energy levels of the highest occupied and lowest unoccupied molecular orbitals of these small molecules were allowed, leading to high open-circuit voltages (Voc) for their solar...

In this study, we incorporated molybdenum disulfide (MoS2) nanosheets into sol–gel processing of zinc oxide (ZnO) to form ZnO:MoS2 composites for use as electron transport layers (ETLs) in inverted...

Several approaches, including the use of small molecule acceptors, novel polymer structures, and tandem cell structures, have been adopted to prepare polymer solar cells displaying high power conversion efficiencies (PCEs). The application of ternary blends as the active layer for polymer solar cells—for which the absorption spectra can be tuned by varying the composition ratios of components—is another facile approach toward optimizing the PCEs of devices. The selection of suitable ternary blends active layer often relies on intuition and remains a formidable challenge. Here, we adopted a systemic approach of not only using the same donor chemical units in the two donor-acceptor (D/A) conjugated polymers with complementary light absorption (energy band gaps) but also varying the side chains architectures as a means of tuning the packing of these semi-planar conjugated polymers, thereby influencing the carrier transport and optimizing the PCE. We employed linear, branch and mixed linear-and-branch side-chain attached benzooxadiazole (BO) as the acceptor (A) units in poly[benzodithiophene-thiophene-benzooxadiazole] (PBDTTBO) conjugated polymers and monitored their interactions with poly[benzodithiophene-fluorothienothiophene] (PTB7-TH), both of which featured the same benzodithiophene (BDTT) donor (D) units. We found that incorporating a minor amount (10%) of D/A conjugated PBDTTBO with such side chains into the PTB7-TH with a fullerene allowed us to tune the packing of the two polymers and, thereby, enhance the PCEs of corresponding ternary blend devices; the PCE of the ternary blend device incorporating PBDTTBO with two branched-side chains, PTB7-TH, and PC 71 BM increased to 11.4% from 9.0% for the device incorporating only the binary blend of PTB7-TH and PC 71 BM—a relative increase of more than 25%. This approach of using side chain engineering to tune the structure of a minor conjugated polymer and, thus, influence the packing of another major conjugated polymer that features the same donor chemical units appears to be an effective means of preparing highly efficient polymer cells.

Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.

We demonstrated a facile and green preparation of cuprous oxide-reduced graphene oxide (Cu2O-rGO) nanoheterostructures through a photochemical reaction. The density of Cu2O nanocubes (NCs) grown on the rGO surface can be well controlled by modulating the concentration of GO employed in the reaction. Because of the relatively low potential of Fermi level of rGO, the photoexcited electrons on the conduction band (CB) of Cu2O NCs preferentially transfer to rGO, simultaneously leaving photogenerated holes on the valence band (VB) of Cu2O, resulting in the notable charge carrier separation properties. Time-resolved photoluminescence (TRPL) spectra were collected to quantitatively analyze the electron transfer rate constant ( k et ) between Cu2O NCs and rGO, and the dependence of the ket on the rGO constituent in Cu2O-rGO nanoheterostructures. Among all the samples tested, the Cu2O-rGO nanoheterostructure with the rGO constituent of 2 wt.% (denoted as Cu2O-rGO-2) displayed the largest ket as well as the most pronounced charge separation property. The optimized Cu2O-rGO-2 showed the best methyl orange (MO) photocatalytic degradation performance, which was highly consistent with the trend of the obtained k et results. As compared with relevant commercial products, such as N-doped P-25 TiO2 and commercial Cu2O powders, the Cu2O-rGO-2 exhibited superior efficiency toward MO degradation under visible light illumination, illustrating its potential for applications in relevant photoelectric conversion processes. The recycling trial showed that the Cu2O-rGO-2 has promising potential for use in the long-term course of photocatalysis to degrade organic pollutants. Furthermore, the photocatalytic efficiency evaluated under natural sunlight demonstrated that the present Cu2O-rGO nanoheterostructure could effectively harvest the energy of solar spectrum and converted it into the chemical energy for organic pollutants degradation. The current study could provide great insights into the design of semiconductor/graphene composites which exhibit remarkable charge separation properties for practical applications in the organic pollutants photodegradation, solar fuel generation as well as photovoltaic devices.

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.