MoS2 Nanoflowers Grown on Plasma-Induced W-Anchored Graphene for Efficient and Stable H2 Production Through Seawater Electrolysis.

Herein, it is found that 3D transition metal dichalcogenide (TMD)-MoS2 nanoflowers-grown on 2D tungsten oxide-anchored graphene nanosheets (MoS2 @W-G) functions as a superior catalyst for the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The optimized weight ratio of MoS2 @W-G (MoS2 :W-G/1.5:1) in 0.5 M H2 SO4 achieves a low overpotential of 78 mV at 10 mA cm-2 , a small Tafel slope of 48 mV dec-1 , and a high exchange current density (0.321 mA cm⁻2 ). Furthermore, the same MoS2 @W-G composite exhibits stable HER performance when using real seawater, with Faradaic efficiencies of 96 and 94% in acidic and alkaline media, respectively. Density functional theory calculations based on the hybrid MoS2 @W-G structure model confirm that suitable hybridization of 3D MoS2 and 2D W-G nanosheets can lower the hydrogen adsorption: Gibbs free energy (∆GH* ) from 1.89 eV for MoS2 to -0.13 eV for the MoS2 @W-G composite. The excellent HER activity of the 3D/2D hybridized MoS2 @W-G composite arises from abundance of active heterostructure interfaces, optimizing the electrical configuration, thereby accelerating the adsorption and dissociation of H2 O. These findings suggest a new approach for the rational development of alternative 3D/2D TMD/graphene electrocatalysts for HER applications using seawater.

High-Performance Poly(3-hexyl thiophene)-Based Organic Photovoltaics with Side-Chain Engineering of Core Units of Small Molecule Acceptors.

In this study, we synthesized a series of four large-band gap small molecule acceptors with side-chain engineering of the dithieno-pyrrolo-fused pentacyclic benzotriazole (BZTTP or Y1 core) or the fused-ring dithienothiophene-pyrrolobenzothiadiazole (TPBT or Y6 core) with difluoro-indene-dione (IO2F) or dichloro-indene-dione (IO2Cl) end groups to form Y1-IO2F, Y1-IO2Cl, Y6-IO2F, and Y6-IO2Cl acceptors, respectively, for blending with poly(3-hexyl thiophene) (P3HT) for bulk heterojunction organic photovoltaics. The complementary UV-vis absorption spectra of these small molecules and P3HT along with their offset energy bands allow broad absorption and effective electron transfer. Through synchrotron wide-angle X-ray scattering (WAXS) analyses and contact angle measurements, we found that the blend of the small molecule Y6-IO2F (having a TPBT core) and P3HT achieves an optimum morphology that balances their crystallinity and miscibility, among those of these four blends, leading to a substantial enhancement in the short-circuit current density and thus power conversion efficiency (PCE) in their devices. For example, the P3HT:Y6-IO2F (w/w: 1/1.2) device exhibited a champion PCE of 10.5% with a short current density (Jsc) value of 15.9 mA/cm2 as compared to the P3HT:Y1-IO2F device having a PCE of 2.2% with a Jsc value of 5.7 mA/cm2 because of the higher Y6-IO2F (with TPBT core) molecular packing that facilitated carrier transport in the devices. The enhanced thermal stability exhibited by the devices incorporating Y6-IO2F and Y6-IO2Cl, as compared to that of Y1-IO2F and Y1-IO2Cl devices, is also due to the more planar TPBT core structure, while the photostability of devices incorporating Y6-IO2Cl and Y1-IO2Cl is better than that of devices incorporating Y6-IO2F and Y1-IO2F, owing to more photostable chemical structures. These results present an outstanding performance for P3HT-based organic solar cells. Moreover, these small molecule blends are processed with an environmentally friendly solvent tetrahydrofuran, demonstrating both the sustainability and commercial viability of these types of organic photovoltaics.

Ion accumulation-induced capacitance elevation in a microporous graphene-based supercapacitor.

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.

Bubble-Channeling Electrophoresis of Honeycomb-Like Chitosan Composites.

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-2 ). The chitosan composite is flexible and is able to maintain sufficient adhesive force toward objects with different surface curvatures.

Perylene Diimide-Fused Dithiophenepyrroles with Different End Groups as Acceptors for Organic Photovoltaics.

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.

High-Performance Organic Solar Cells Featuring Double Bulk Heterojunction Structures with Vertical-Gradient Selenium Heterocyclic Nonfullerene Acceptor Concentrations.

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.

Surface Reconstruction of Halide Perovskites During Post-treatment.

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.

High-Performance Organic Photovoltaics Incorporating an Active Layer with a Few Nanometer-Thick Third-Component Layer on a Binary Blend Layer.

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.

Pentafluoropyridine functionalized novel heteroatom-doped with hierarchical porous 3D cross-linked graphene for supercapacitor 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 (G T) 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.

Incorporating Indium Selenide Nanosheets into a Polymer/Small Molecule Binary Blend Active Layer Enhances the Long-Term Stability and Performance of Its Organic Photovoltaics.

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.

Enabling High-Performance Tandem Organic Photovoltaic Cells by Balancing the Front and Rear Subcells.

In tandem organic photovoltaics, the front subcell is based on large-bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a narrow-bandgap acceptor for infrared absorption but a large-bandgap donor to realize a high open-circuit voltage. Unfortunately, most of the ultraviolet-visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large-bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole-transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared-absorbing polymer donor as a third component is introduced, which provides a second hole-generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short-circuit current density of the two-terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7 mA cm-2 (while retaining the open-circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.

Transparent Hole-Transporting Frameworks: A Unique Strategy to Design High-Performance Semitransparent Organic Photovoltaics.

Thanks to the nature of molecular orbitals, the absorption spectra of organic semiconductors are not continuous like those in traditional inorganic semiconductors, which offers a unique application of organic photovoltaics (OPVs): semitransparent OPVs. Recently, the exciting progress of materials design has promoted the development of semitransparent OPVs. However, in the perspective of device engineering, almost all reported works reduce the thickness of back/reflected electrode to obtain high average visible transmittance (AVT), which is a trade-off between power conversion efficiency (PCE) and the transmittance of the whole solar spectrum (visible and infrared), and therefore limit the further development. Herein, a unique strategy of "transparent hole-transporting frameworks" is proposed. A hole-transporting large-bandgap polymer (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA)) is employed to partially replace polymer donors in the active layer of PBDB-T/Y1. PTAA is a p-type polymer with a large bandgap of 2.9 eV; the partial substitution of PBDB-T by PTAA reduces the absorption of the active layer only in the visible region, keeping the hole-transporting pathways as well as the optimized film morphology. As a result, semitransparent OPVs with PCEs of 12% and AVTs of 20% are achieved, both on rigid and flexible substrates. To demonstrate the generality, this strategy is also used in three different active layers.

Transparent Flexible Heteroepitaxy of NiO Coated AZO Nanorods Arrays on Muscovites for Enhanced Energy Storage Application.

Transparent flexible energy storage devices are considered as important chains in the next-generation, which are able to store and supply energy for electronic devices. Here, aluminum-doped zinc oxide (AZO) nanorods (NRs) and nickel oxide (NiO)-coated AZO NRs on muscovites are fabricated by a radio frequency (RF) magnetron sputtering deposition method. Interestingly, AZO NRs and AZO/NiO NRs are excellent electrodes for energy storage application with high optical transparency, high conductivity, large surface area, stability under compressive and tensile strain down to a bending radius of 5 mm with 1000 bending cycles. The obtained symmetric solid-state supercapacitors based on these electrodes exhibit good performance with a large areal specific capacitance of 3.4 mF cm-2 , long cycle life 1000 times, robust mechanical properties, and high chemical stability. Furthermore, an AZO/NiO//Zn battery based on these electrodes is demonstrated, yielding a discharge capacity of 195 mAh g-1 at a current rate of 8 A g-1 and a discharge capacity of over 1000 cycles with coulombic efficiency to 92%. These results deliver a concept of opening a new opportunity for future applications in transparent flexible energy storage.

Synthesis of IrO2 decorated core-shell PS@PPyNH2 microspheres for bio-interface application.

In this paper, an effective approach is demonstrated for the fabrication of IrO2-decorated polystyrene@functionalized polypyrrole (core@shell; PS@PPyNH2) microspheres. The synthesis begins with the preparation of monodispersive PS microspheres with a diameter of 490 nm, by a process of emulsifier-free emulsion polymerization, followed by a copolymerization process involving pyrrole and PyNH2 monomers in a PS microsphere aqueous suspension, to produce uniform PS@PPyNH2 microspheres with a diameter of 536 nm. The loading of 2 nm IrO2 nanoparticles onto the PS@PPyNH2 microspheres can be easily adjusted by tuning the pH value of the IrO2 colloidal solution and the PS@PPyNH2 suspension. At pH 4, we successfully obtain IrO2-decorated PS@PPyNH2 microspheres via electrostatic attraction and hydrogen bonding simultaneously between the negatively-charged IrO2 nanoparticles and the positively-charged PS@PPyNH2 microspheres. These IrO2-decorated PS@PPyNH2 microspheres exhibit a characteristic cyclic voltammetric profile, similar to that of an IrO2 thin film. The charge storage capacity is 5.19 mA cm-2, a value almost five times greater than that of PS@PPyNH2 microspheres. In addition, these IrO2-decorated PS@PPyNH2 microspheres exhibit excellent cell viability and biocompatibility.

Plasma-Induced Exfoliation Provides Onion-Like Graphene-Surrounded MoS2 Nanosheets for a Highly Efficient Hydrogen Evolution Reaction.

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 MoS2 nanosheets engulfed within onion-like graphene nanosheets (OGNs@MoS2). The resultant OGNs@MoS2 structures not only increased the number of active sites of the semiconducting MoS2 nanosheets but also enhanced their conductivity. Our OGNs@MoS2 composites exhibited high HER performance, characterized by a low overpotential of 118 mV at a current density of 10 mA cm-2, a Tafel slope of 73 mV dec-1, and long-time stability of 105 s without degradation; this performance is much better than that of the sheet-like graphene-wrapped MoS2 composite GNs@MoS2 (182 mV, 82 mV dec-1) and is among the best ever reported for composites involving MoS2 and graphene nanosheets prepared through a simple one-batch process and using a low temperature and a short time for the HER. This approach appears to be an effective and simple strategy for tuning the morphologies of composites of graphene and transition metal dichalcogenide materials for a broad range of energy applications.

Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics.

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.

Role of precursors mixing sequence on the properties of CoMn2O4 cathode materials and their application in pseudocapacitor.

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%.

Rational Tuning of Molecular Interaction and Energy Level Alignment Enables High-Performance Organic Photovoltaics.

The performance of organic photovoltaics (OPVs) has rapidly improved over the past years. Recent work in material design has primarily focused on developing near-infrared nonfullerene acceptors with broadening absorption that pair with commercialized donor polymers; in the meanwhile, the influence of the morphology of the blend film and the energy level alignment on the efficiency of charge separation needs to be synthetically considered. Herein, the selection rule of the donor/acceptor blend is demonstrated by rationally considering the molecular interaction and energy level alignment, and highly efficient OPV devices using both-fluorinated or both-nonfluorinated donor/acceptor blends are realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, the devices based on the PBDB-T-F/Y1-4F blend and PBDB-T-F/Y6 exhibit champion power conversion efficiencies as high as 14.8% and 15.9%, respectively.

Hydrogen plasma-treated MoSe2 nanosheets enhance the efficiency and stability of organic photovoltaics.

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.

Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component.

Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (VOC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and VOC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.