Sulfated Graphene Oxide as a Hole-Extraction Layer in High-Performance Polymer Solar Cells

Advances in Hole Transport Materials for Layered Casting Solar Cells

Huge energy consumption and running out of fossil fuels has led to the advancement of renewable sources of power, including solar, wind, and tide. Among them, solar cells have been well developed with the significant achievement of silicon solar panels, which are popularly used as windows, rooftops, public lights, etc. In order to advance the application of solar cells, a flexible type is highly required, such as layered casting solar cells (LCSCs). Organic solar cells (OSCs), perovskite solar cells (PSCs), or dye-sensitive solar cells (DSSCs) are promising LCSCs for broadening the application of solar energy to many types of surfaces. LCSCs would be cost-effective, enable large-scale production, are highly efficient, and stable. Each layer of an LCSC is important for building the complete structure of a solar cell. Within the cell structure (active material, charge carrier transport layer, electrodes), hole transport layers (HTLs) play an important role in transporting holes to the anode. Recently, diverse HTLs from inorganic, organic, and organometallic materials have emerged to have a great impact on the stability, lifetime, and performance of OSC, PSC, or DSSC devices. This review summarizes the recent advances in the development of inorganic, organic, and organometallic HTLs for solar cells. Perspectives and challenges for HTL development and improvement are also highlighted.

Application of Graphene-Related Materials in Organic Solar Cells

Graphene-related materials (GRMs) such as graphene quantum dots (GQDs), graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoribbons (GNRs), and so forth have recently emerged as photovoltaic (PV) materials due to their nanodimensional structure and outstanding properties such as high electrical and thermal conductivity, large specific surface, and unique combination of mechanical strength and flexibility. They can be a crucial part of transparent electrodes, hole/electron transport materials, and active layers in organic solar cells (OSCs). Besides their role in charge extraction and transport, GRMs act as device protectors against environmental degradation through their compact bidimensional structure and offer good durability. This review briefly presents the synthesis methods of GRMs and describes the current progress in GRM-based OSCs. PV parameters (short circuit current, open circuit voltage, power conversion efficiency, and fill factor) are summarized and comparatively discussed for the different structures. The efficiency recently surpassed 15% for an OSC incorporating polymer-modified graphene as a transparent electrode. The long-term stability of OSCs incorporating GRMs is also discussed. Finally, conclusions and the outlook for future investigation into GRM-based devices for PVs are presented.

Solution-processed two-dimensional materials for next-generation photovoltaics

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to "on-demand" tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic-inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

Graphene Oxide of Extra High Oxidation: A Wafer for Loading Guest Molecules

We present a new modification of graphene oxide with very high content (85 wt %) of oxygen-containing functional groups (hydroxy, epoxy, lactol, carboxyl, and carbonyl groups) that forms stable aqueous dispersion in up to 9 g·L^-1 concentration solutions. A novel faster method of the synthesis is described that produces up to 1 kg of the material and allows controlling the particle size in solution. The synthesized compound was characterized by various physicochemical methods and molecular dynamics modeling, revealing a unique structure in the form of a multilayered wafer of several sheets thick, where each sheet is highly corrugated. The ragged structure of the sheets forms pockets with hindered mobility of water that leads to the possibility of trapping guest molecules.

Recent Progress in Carbon-Based Buffer Layers for Polymer Solar Cells

Carbon-based materials are promising candidates as charge transport layers in various optoelectronic devices and have been applied to enhance the performance and stability of such devices. In this paper, we provide an overview of the most contemporary strategies that use carbon-based materials including graphene, graphene oxide, carbon nanotubes, carbon quantum dots, and graphitic carbon nitride as buffer layers in polymer solar cells (PSCs). The crucial parameters that regulate the performance of carbon-based buffer layers are highlighted and discussed in detail. Furthermore, the performances of recently developed carbon-based materials as hole and electron transport layers in PSCs compared with those of commercially available hole/electron transport layers are evaluated. Finally, we elaborate on the remaining challenges and future directions for the development of carbon-based buffer layers to achieve high-efficiency and high-stability PSCs.

Solution-Processed PEDOT:PSS/MoS2 Nanocomposites as Efficient Hole-Transporting Layers for Organic Solar Cells

An efficient hole-transporting layer (HTL) based on functionalized two-dimensional (2D) MoS₂-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composites has been developed for use in organic solar cells (OSCs). Few-layer, oleylamine-functionalized MoS₂ (FMoS₂) nanosheets were prepared via a simple and cost-effective solution-phase exfoliation method; then, they were blended into PEDOT:PSS, a conducting conjugated polymer, and the resulting hybrid film (PEDOT:PSS/FMoS₂) was tested as an HTL for poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) OSCs. The devices using this hybrid film HTL showed power conversion efficiencies up to 3.74%, which is 15.08% higher than that of the reference ones having PEDOT:PSS as HTL. Atomic force microscopy and contact angle measurements confirmed the compatibility of the PEDOT:PSS/FMoS₂ surface for active layer deposition on it. The electrical impedance spectroscopy analysis revealed that their use minimized the charge-transfer resistance of the OSCs, consequently improving their performance compared with the reference cells. Thus, the proposed fabrication of such HTLs incorporating 2D nanomaterials could be further expanded as a universal protocol for various high-performance optoelectronic devices.

2D-Organic Hybrid Heterostructures for Optoelectronic Applications

The unique properties of hybrid heterostructures have motivated the integration of two or more different types of nanomaterials into a single optoelectronic device structure. Despite the promising features of organic semiconductors, such as their acceptable optoelectronic properties, availability of low-cost processes for their fabrication, and flexibility, further optimization of both material properties and device performances remains to be achieved. With the emergence of atomically thin 2D materials, they have been integrated with conventional organic semiconductors to form multidimensional heterostructures that overcome the present limitations and provide further opportunities in the field of optoelectronics. Herein, a comprehensive review of emerging 2D-organic heterostructures-from their synthesis and fabrication to their state-of-the-art optoelectronic applications-is presented. Future challenges and opportunities associated with these heterostructures are highlighted.

Rapid Size-Based Protein Discrimination inside Hybrid Isoporous Membranes

Owing to their unique morphology, isoporous membranes derived from block copolymers (BCPs) have rapidly advanced the process of macromolecular separation. In such separations, fouling is the most daunting challenge, affecting both the permeability and selectivity of high-performance isoporous membranes. To overcome this, we increase the hydrophilicity of nanostructured BCP isoporous membranes by incorporating hydrophilic polymer-grafted graphene oxide nanosheets into them. Due to the synergy of these two highly functional components, the hybrid isoporous membranes show pH-responsive and alcohol-gating behaviors, along with improved bactericidal capabilities. Leveraging the high permeability and selectivity behavior of BCP isoporous membranes together with the antifouling capabilities imparted by the polymer-grafted graphene oxide nanosheets, we achieved the highest separation factor (33) ever obtained during the ultrafiltration of the common blood proteins bovine serum albumin and immunoglobulin. This was accompanied by a 60% enhanced flux compared to that of the pristine BCP membranes during this challenging size-based separation of a protein mixture. We surmise that such fouling-resistant hybrid isoporous membranes with rationally functionalized filler materials can be used to replace existing membranes for specific energy-efficient bioseparation applications with improved performance.

The Role of Graphene and Other 2D Materials in Solar Photovoltaics

2D materials have attracted considerable attention due to their exciting optical and electronic properties, and demonstrate immense potential for next-generation solar cells and other optoelectronic devices. With the scaling trends in photovoltaics moving toward thinner active materials, the atomically thin bodies and high flexibility of 2D materials make them the obvious choice for integration with future-generation photovoltaic technology. Not only can graphene, with its high transparency and conductivity, be used as the electrodes in solar cells, but also its ambipolar electrical transport enables it to serve as both the anode and the cathode. 2D materials beyond graphene, such as transition-metal dichalcogenides, are direct-bandgap semiconductors at the monolayer level, and they can be used as the active layer in ultrathin flexible solar cells. However, since no 2D material has been featured in the roadmap of standard photovoltaic technologies, a proper synergy is still lacking between the recently growing 2D community and the conventional solar community. A comprehensive review on the current state-of-the-art of 2D-materials-based solar photovoltaics is presented here so that the recent advances of 2D materials for solar cells can be employed for formulating the future roadmap of various photovoltaic technologies.

Constructing Continuous Proton-Conducting Highways within Sulfonated Poly(Arylene Ether Nitrile) Composite Membrane by Incorporating Amino-Sulfo-Bifunctionalized GO

To obtain a proton exchange membrane (PEM) with high proton conductivity and low methanol permeability, a novel amino-sulfo-bifunctionalized GO (NSGO) was synthesized and explored as a filler for sulfonated poly(arylene ether nitrile) (SPEN). The result indicated that the microstructure of composite membranes was rearranged by NSGO and strong acid⁻base interactions were formed between fillers and the SPEN matrix, affording enhanced thermal, mechanical, and dimensional stabilities. Moreover, it was found that NSGO fillers were uniformly dispersed in the SPEN matrix, generating efficient proton-conducting paths along the SPEN/NSGO interface. Meanwhile, the sulfonic and amino groups of NSGO served as additional proton hopping sites to connect the ionic clusters in the SPEN matrix, creating interconnected and long-range ionic pathways. In such a way, proton-conducting highways with low energy barriers are constructed, which enhance the proton conductivity of the composite membranes via the Grotthuss mechanism. Furthermore, the composite membranes also effectively prevent methanol permeation, and therefore high selectivity (the ratio of proton conductivity and methanol permeability) is endowed. Compared to SPEN membrane, a 3.6-fold increase in selectivity is obtained for the optimal composite membrane. This study will provide a new strategy for the preparation of high-performance PEM.

Noncovalent phosphorylation of graphene oxide with improved hole transport in high-efficiency polymer solar cells

Graphene oxide (GO) has been extensively applied as an alternative hole transport layer (HTL) of bulk heterojunction polymer solar cells (BHJ-PSCs) with the function of selectively transporting holes and blocking electrons, but suffers from low electrical conductivity. Herein, using phosphorus pentoxide (P2O5) dissolved in methanol as a precursor, we successfully modified GO via noncovalent phosphorylation for the first time, which showed improved hole transport in BHJ-PSCs compared to the pristine GO. As a result, BHJ-PSC devices based on noncovalently phosphorylated GO (P-GO) HTL show dramatically higher power conversion efficiencies (7.90%, 6.59%, 3.85% for PTB7:PC71BM, PBDTTT-C:PC71BM, P3HT:PC61BM, respectively) than those of the corresponding control devices based on the pristine GO HTL (6.28%, 5.07%, 2.78%), which are comparable to those of devices based on the most widely used HTL-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).

Sulfanilic Acid Pending on a Graphene Scaffold: Novel, Efficient Synthesis and Much Enhanced Polymer Solar Cell Efficiency and Stability Using It as a Hole Extraction Layer

In this contribution, we describe a novel, facile, and scalable methodology for high degree functionalization toward graphene by the reaction between bulk graphite fluoride and in situ generated amine anion. Using this, the rationally designed sulfanilic acid pending on a graphene scaffold (G-SO₃H), a two-dimensional (2D) π-conjugated counterpart of poly(styrenesulfonate), is available. Combined reliable characterizations demonstrate that a very large quantity of sulfanilic blocks are linked to graphene through the foreseen substitution of carbon-fluorine units and an unexpected reductive defluorination simultaneously proceeds during the one-step reaction, endowing the resultant G-SO₃H with splendid dispersity in various solvents and film-forming property via the former, and with recovered 2D π-conjugation via the latter. Besides, the work function of G-SO₃H lies at -4.8 eV, well matched with the P3HT donor. Awarded with these fantastic merits, G-SO₃H behaves capable in hole collection and transport, indicated by the enhanced device efficiency and stability of polymer solar cells (PSCs) based on intensively studied P3HT:PCBM blends as an active layer. In particular, comparison with conventional poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) and recently rising and shining graphene oxide, G-SO₃H outperforms above 17 and 24%, respectively, in efficiency. More impressively, when these three unencapsulated devices are placed in a N₂-filled glovebox at around 25 °C for 7 weeks, or subject to thermal treatment at 150 °C for 6 h also in N₂ atmosphere, or even rudely exposed to indoor air, G-SO₃H-based PSCs exhibit the best stability. These findings enable G-SO₃H to be a strongly competitive alternative of the existing hole extraction materials for PSC real-life applications.

Poly(2,5-benzimidazole)-Grafted Graphene Oxide as an Effective Proton Conductor for Construction of Nanocomposite Proton Exchange Membrane

To improve proton conduction properties of conventional sulfonated poly(ether ether ketone) (SPEEK), poly(2,5-benzimidazole)-grafted graphene oxide (ABPBI-GO) was prepared to fabricate nanocomposite membranes, which then were further doped with phosphoric acid (PA). The ABPBI-GO was synthesized through the reaction of 3,4-diaminobenzoic acid with the carboxyl acid groups present on the GO surface. The simultaneous incorporation of ABPBI-GO and PA into SPEEK did not only improve the physicochemical performance of the membranes in terms of thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeation resistance but also relieve PA leaching from the membranes though acid-base interactions. The resulting composite membranes exhibited enhanced proton conductivities in extended humidity ranges thanks to the hygroscopic character of PA and the increased water uptake. Moreover, the unique self-ionization, self-dehydration, and nonvolatile properties of PA improved the high-temperature proton conductivities (σ) of PA-doped membranes. The PA-doped SPEEK/ABPBI-GO-3.0 delivered a σ of 7.5 mS cm^-1 at 140 °C/0% RH. This value was fourfold higher than that of pristine SPEEK membranes. The PA-doped SPEEK/ABPBI-GO-3.0 based fuel cell membranes delivered power densities of 831.06 and 72.25 mW cm^-2 at 80 °C/95% RH and 120 °C/0% RH, respectively. By contrast, the PA-doped SPEEK membrane generated only 655.63 and 44.58 mW cm^-2 under the same testing conditions.

Graphene Oxide by UV-Ozone Treatment as an Efficient Hole Extraction Layer for Highly Efficient and Stable Polymer Solar Cells

The hole extraction layer has a significant impact on the achievement of high-efficiency polymer solar cells (PSCs). Here, we report an efficient approach to direct UV-ozone treatment by larger device performance enhancement employing graphene oxide (GO). The dramatic performance enhancement of PSCs with the P3HT:PCBM blend as an active layer was demonstrated by the UV-ozone treatment of GO for 30 min: best power conversion efficiency (PCE) of 4.18%, fill factor of 0.63, J_sc of 10.94 mA cm^-2, and V_oc of 0.61 V, which are significantly higher than those of the untreated GO (1.82%) and highly comparable PEDOT:PSS-based PSCs (3.73%). In addition, PSCs with UV-ozone-treated GO showed a longer stability than PSCs with PEDOT:PSS. The significant enhancement of PCEs of PSCs can be attributed to the fact that ozone molecules can oxidize GO into CO₂ and leave highly conductive graphene particles. We suggest that this simple UV-ozone treatment can provide an efficient method for highly efficient GO hole extraction in high-performance PSCs.

One-Pot Large-Scale Synthesis of Carbon Quantum Dots: Efficient Cathode Interlayers for Polymer Solar Cells

Cathode interlayers (CILs) with low-cost, low-toxicity, and excellent cathode modification ability are necessary for the large-scale industrialization of polymer solar cells (PSCs). In this contribution, we demonstrated one-pot synthesized carbon quantum dots (C-dots) with high production to serve as efficient CIL for inverted PSCs. The C-dots were synthesized by a facile, economical microwave pyrolysis in a household microwave oven within 7 min. Ultraviolet photoelectron spectroscopy (UPS) studies showed that the C-dots possessed the ability to form a dipole at the interface, resulting in the decrease of the work function (WF) of cathode. External quantum efficiency (EQE) measurements and 2D excitation-emission topographical maps revealed that the C-dots down-shifted the high energy near-ultraviolet light to low energy visible light to generate more photocurrent. Remarkably improvement of power conversion efficiency (PCE) was attained by incorporation of C-dots as CIL. The PCE was boosted up from 4.14% to 8.13% with C-dots as CIL, which is one of the best efficiency for i-PSCs used carbon based materials as interlayers. These results demonstrated that C-dots can be a potential candidate for future low cost and large area PSCs producing.

Preparation of Reduced Graphene Oxide:ZnO Hybrid Cathode Interlayer Using In Situ Thermal Reduction/Annealing for Interconnecting Nanostructure and Its Effect on Organic Solar Cell

A novel hybrid cathode interlayer (CIL) consisting of reduced graphene oxide and zinc oxide (ZnO) is realized in the inverted organic solar cells (OSCs). A dual-nozzle spray coating system and facile one-step in situ thermal reduction/annealing (ITR/ITA) method are introduced to precisely control the components of the CIL, assemble ZnO with graphene oxide, and reduce graphene oxide into in situ thermal reduced graphene oxide (IT-RGO), simultaneously. The ZnO:IT-RGO hybrid CIL shows high electric conductivity, interconnecting nanostructure, and matched energy level, which leads to a significant enhancement in the power conversion efficiency from 6.16% to 8.04% for PTB7:PC₇₁BM and from 8.02% to 9.49% for PTB7-Th:PC₇₁BM-based OSCs, respectively. This newly developed spray-coated ZnO:IT-RGO hybrid CIL based on one-step ITR/ITA treatment has the high potential to provide a facile pathway to fabricate the large-scale, fast fabrication, and high performance OSCs.

Significantly improved photovoltaic performance in polymer bulk heterojunction solar cells with graphene oxide /PEDOT:PSS double decked hole transport layer

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC₇₁BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability.

Efficiency enhancement in inverted planar perovskite solar cells by synergetic effect of sulfated graphene oxide (sGO) and PEDOT:PSS as hole transporting layer

We report a simple solution route for preparing a sGO-PEDOT composite HTL by combining solution-processable sGO with commercialized PEDOT:PSS solution. The PSCs based on these sGO-PEDOT composite HTLs were systematically investigated.

Graphene-Perovskite Solar Cells Exceed 18 % Efficiency: A Stability Study

Interface engineering is performed by the addition of graphene and related 2 D materials (GRMs) into perovskite solar cells (PSCs), leading to improvements in the power conversion efficiency (PCE). By doping the mesoporous TiO₂ layer with graphene flakes (mTiO₂ +G), produced by liquid-phase exfoliation of pristine graphite, and by inserting graphene oxide (GO) as an interlayer between the perovskite and hole-transport layers, using a two-step deposition procedure in air, we achieved a PCE of 18.2 %. The obtained PCE value mainly results from improved charge-carrier injection/collection with respect to conventional PSCs. Although the addition of GRMs does not influence the shelf life, it is beneficial for the stability of PSCs under several aging conditions. In particular, mTiO₂ +G PSCs retain more than 88 % of the initial PCE after 16 h of prolonged 1 sun illumination at the maximum power point. Moreover, when subjected to prolonged heating at 60 °C, the GO-based structures show enhanced stability with respect to mTiO₂ +G PSCs, as a result of thermally induced modification at the mTiO₂ +G/perovskite interface. The exploitation of GRMs in the form of dispersions and inks opens the way for scalable large-area production, advancing the possible commercialization of PSCs.

Recent Advances in Interface Engineering for Planar Heterojunction Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells are considered as one of the most promising next-generation solar cells due to their advantages of low-cost precursors, high power conversion efficiency (PCE) and easy of processing. In the past few years, the PCEs have climbed from a few to over 20% for perovskite solar cells. Recent developments demonstrate that perovskite exhibits ambipolar semiconducting characteristics, which allows for the construction of planar heterojunction (PHJ) perovskite solar cells. PHJ perovskite solar cells can avoid the use of high-temperature sintered mesoporous metal oxides, enabling simple processing and the fabrication of flexible and tandem perovskite solar cells. In planar heterojunction materials, hole/electron transport layers are introduced between a perovskite film and the anode/cathode. The hole and electron transporting layers are expected to enhance exciton separation, charge transportation and collection. Further, the supporting layer for the perovskite film not only plays an important role in energy-level alignment, but also affects perovskite film morphology, which have a great effect on device performance. In addition, interfacial layers also affect device stability. In this review, recent progress in interfacial engineering for PHJ perovskite solar cells will be reviewed, especially with the molecular interfacial materials. The supporting interfacial layers for the optimization of perovskite films will be systematically reviewed. Finally, the challenges remaining in perovskite solar cells research will be discussed.

Inverted organic photovoltaic cells

The advance in lifestyle, modern industrialization and future technological revolution are always at high expense of energy consumption. Unfortunately, there exist serious issues such as limited storage, high cost and toxic contamination in conventional fossil fuel energy sources. Instead, solar energy represents a renewable, economic and green alternative in the future energy market. Among the photovoltaic technologies, organic photovoltaics (OPVs) demonstrate a cheap, flexible, clean and easy-processing way to convert solar energy into electricity. However, OPVs with a conventional device structure are still far away from industrialization mainly because of their short lifetime and the energy-intensive deposition of top metal electrode. To address the stability and cost issue simultaneously, an inverted device structure has been introduced into OPVs, bridging laboratory research with practical application. In this review, recent progress in device structures, working mechanisms, functions and advances of each component layer as well their correlations with the efficiency and stability of inverted OPVs are reviewed and illustrated.

Constructing Ionic Liquid-Filled Proton Transfer Channels within Nanocomposite Membrane by Using Functionalized Graphene Oxide

Herein, nanocomposite membranes are fabricated based on functionalized graphene oxides (FGOs) and sulfonated poly(ether ether ketone) (SPEEK), followed by being impregnated with imidazole-type ionic liquid (IL). The functional groups (acidic group or basic group) on FGOs generate strong interfacial interactions with SPEEK chains and then adjust their motion and stacking. As a result, the nanocomposite membranes possess tunable interfacial domains as determined by its free volume characteristic, which provides regulated location for IL storage. The stored ILs act as hopping sites for water-free proton conduction along the FGO-constructed interfacial channels. The microstructure at SPEEK-FGO interface governs the IL uptake and distribution in nanocomposite membrane. Different from GO and vinyl imidazole functionalized GO (VGO), the presence of acidic (-SO3H) groups confers the p-styrenesulfonic acid functionalized GO (SGO) incorporated nanocomposite membrane loose interface and strong electrostatic attraction with imidazole-type IL, imparting an enhanced IL uptake and anhydrous proton conductivity. Nanocomposite membrane containing 7.5% SGO attains the maximum IL uptake of 73.7% and hence the anhydrous conductivity of 21.9 mS cm(-1) at 150 °C, more than 30 times that of SPEEK control membrane (0.69 mS cm(-1)). In addition, SGOs generate electrostatic attractions to the ILs confined within SGO-SPEEK interface, affording the nanocomposite membrane enhanced IL retention ability.

Functionalized carbon nanotubes and graphene-based materials for energy storage

This feature article summarizes recent progress in the functionalization of carbon nanotubes and graphene for energy storage applications in supercapacitors and batteries.

Graphene oxide: strategies for synthesis, reduction and frontier applications

In this review article, we describe a general introduction to GO, its synthesis, reduction and some selected frontier applications. Its low cost and potential for mass production make GO a promising building block for functional hybrid materials.

Facile and Scalable Preparation of Graphene Oxide-Based Magnetic Hybrids for Fast and Highly Efficient Removal of Organic Dyes

This study reports the facile preparation and the dye removal efficiency of nanohybrids composed of graphene oxide (GO) and Fe3O4 nanoparticles with various geometrical structures. In comparison to previously reported GO/Fe3O4 composites prepared through the one-pot, in situ deposition of Fe3O4 nanoparticles, the GO/Fe3O4 nanohybrids reported here were obtained by taking advantage of the physical affinities between sulfonated GO and Fe3O4 nanoparticles, which allows tuning the dimensions and geometries of Fe3O4 nanoparticles in order to decrease their contact area with GO, while still maintaining the magnetic properties of the nanohybrids for easy separation and adsorbent recycling. Both the as-prepared and regenerated nanohybrids demonstrate a nearly 100% removal rate for methylene blue and an impressively high removal rate for Rhodamine B. This study provides new insights into the facile and controllable industrial scale fabrication of safe and highly efficient GO-based adsorbents for dye or other organic pollutants in a wide range of environmental-related applications.

Stability enhancement of organic photovoltaic devices utilizing partially reduced graphene oxide as the hole transport layer: nanoscale insight into structural/interfacial properties and aging effects

A powerful insight into the structural and interfacial properties of post-fabricated bulk heterojunction (BHJ) organic photovoltaic (OPV) devices, utilizing partially reduced graphene oxide as the hole transport layer, is reported.

A comprehensive study of sulfonated carbon materials as conductive composites for polymer solar cells

The sulfonated graphene lamellae are favorable to bridge the PEDOT islands, which significantly improves the conductivity.

Control of the oxidation level of graphene oxide for high efficiency polymer solar cells

Achieving high efficiency polymer solar cells by controlling the oxidation level of graphene oxide.