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The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence–excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication or by electronic-type sorting, both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched through efficient energy transfer from the inner to the outer DWCNT walls. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples.

The functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) with luminescent sp$^{3}$ defects creates red-shifted emission features in the near-infrared and boosts their photoluminescence quantum yields (PLQYs). While multiple synthetic routes for the selective introduction of sp$^{3}$ defects have been developed, a convenient metric to precisely quantify the number of defects on a SWCNT lattice is not available. Here, we present a direct and simple quantification protocol based on a linear correlation of the integrated Raman D/G$^{+}$ signal ratios and defect densities as extracted from PLQY measurements. Corroborated by a statistical analysis of single-nanotube emission spectra at cryogenic temperature, this method enables the quantitative evaluation of sp$^{3}$ defect densities in (6,5) SWCNTs with an error of $\pm$ 3 defects per micrometer and the determination of oscillator strengths for different defect types. The developed protocol requires only standard Raman spectroscopy and is independent of the defect configuration, dispersion solvent and nanotube length.

Small perturbations in the structure of materials significantly affect their properties. One example are single wall carbon nanotubes (SWCNTs), which exhibit chirality-dependent near infrared (NIR) fluorescence. They can be modified with quantum defects through the reaction with diazonium salts and the number or distribution of these defects determine their photophysics. However, the presence of multiple chiralities in typical SWCNT samples complicates the identifica-tion of defect-related emission features. Here, we show that quantum defects do not affect aqueous two-phase extraction (ATPE) of different SWCNT chiralities into different phases, which pinpoints to low numbers of defects. For bulk samples the bandgap emission (E11) of monochiral (6,5)-SWCNTs decreases and the defect related emission feature (E11*) increas-es with diazonium salt concentration and represents a proxy for the defect number. The high purity of monochiral sam-ples from ATPE allows us to image NIR fluorescence contributions (E11 = 986 nm, and E11* = 1140 nm) on the single SWCNT level. Interestingly, we observe a stochastic (Poisson) distribution of quantum defects. SWCNTs have most-likely 1 to 3 defects (for low to high (bulk) quantum defect densities). Additionally, we verify this number by following single reaction events that appear as discrete steps in the temporal fluorescence traces. We thereby count single reactions via NIR imaging and demonstrate that stochasticity plays a crucial role for the optical properties of SWCNTs. These results show that there can be a large discrepancy between ensemble and single particle experiments/properties of nanomateri-als.

Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a 2D order parameter, S2D, approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, three different patterns with radial symmetry and an area of 3.8 cm2 are created. Two of these patterns are replicated by the filtered SWCNTs and S2D values of ≈0.85 are obtained. Each of the radially aligned SWCNT films is characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial, and azimuthal polarized light fields. The former is used to define a novel indicator akin to the 2D order parameter using Malu's law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries.

Single wall carbon nanotubes (SWCNTs) have long been proposed as a candidate to enhance existing photovoltaic materials by providing an extension to the light absorbed in the infrared. In this work, we discuss the validity of this statement for silicon solar cells and couple a bifacial silicon solar cell to an organic SWCNT cell in a 4-terminal stack. Single chiral species of (6,5), (7,6), and (10,3) are used in the organic cell and the overall contribution to photocurrent from the SWCNTs is discussed in terms of the diameter dependent quantum efficiency, film thickness, the transmittance of silicon, the spectral overlap of the SWCNT's absorbance with the solar irradiance spectrum and the maximum obtainable current density in the infrared.

The innate inverse Auger effect within bulk silicon can result in multiple carrier generation. Observation of this effect is reliant upon low high-energy photon reflectance and high-quality surface passivation. In the photovoltaics industry, metal-assisted chemical etching (MACE) to afford black silicon (b-Si) can provide a low high-energy photon reflectance. However, an industrially feasible and cheaper technology to conformally passivate the outer-shell defects of these nanowires is currently lacking. Here, a technology is introduced to infiltrate black silicon nanopores with a simple and vacuum-free organic passivation layer that affords millisecond-level minority carrier lifetimes and matches perfectly with existing solution-based processing of the MACE black silicon. Advancements such as the demonstration of an excellent passivation effect whilst also being low reflectance provide a new technological route for inverse Auger multiple carrier generation and an industrially feasible technical scheme for the development of the MACE b-Si solar cells.

The 1D confinement of silicon in the form of a nanowire revives its newness with the emergence of new optical and electronic properties. However, the development of a production process for silicon nanowires (SiNWs) having a high quality crystalline core and exhibiting good stability in solution with effective outer-shell defect passivation is still a challenge. In this work, SiNWs are prepared from a silicon wafer using solution processing steps, and importantly outer-shell-defect passivation is achieved by in situ grafting of organic molecules based on thin films. Defect passivation and the high quality of the SiNWs are confirmed with thin films on glass and flexible plastic substrates. A dramatic enhancement in both the fluorescence lifetime and infrared photoluminescence is observed. The in situ organic passivation of SiNWs has potential application in all low-dimensional silicon devices including infrared detectors, solar cells and lithium-ion battery anodes.

A breakthrough in graphene-oxide/silicon heterojunction solar cells is presented in which edge-oxidized graphene and an in-plane charge transfer dopant (Nafion) are combined to form a high-quality passivating contact scheme. A graphene oxide (GO):Nafion ink is developed and an advanced back-junction GO:Nafion/n-Si solar cell with a high-power conversion efficiency (18.8%) and large area (5.5 cm2) is reported. This scalable solution-based processing technique has the potential to enable low-cost carbon/silicon heterojunction photovoltaic devices.

Plants use secondary metabolites such as polyphenols for chemical defense against pathogens and herbivores. Despite their importance in plant pathogen interactions and tolerance to diseases, it remains challenging to detect polyphenols in complex plant tissues. Here, we create molecular sensors for plant polyphenol imaging that are based on near-infrared (NIR) fluorescent single wall carbon nanotubes (SWCNTs). We identified polyethylene glycol-phospholipids that render (6,5)-SWCNTs sensitive (Kd = 90 nM) to plant polyphenols (tannins, flavonoids, ...), which red-shift (up to 20 nm) and quench their emission (~1000 nm). These sensors report changes in total polyphenol level after herbivore or pathogen challenge in crop plant systems (Soybean Glycine max) and leaf tissue extracts (Tococa spp). We furthermore demonstrate remote chemical imaging of pathogen-induced polyphenol release from roots of soybean seedlings over the time course of 24h. Additional use of chirality-pure polyphenol sensors gives further access to ratiometric sensing and imaging applications. Overall, this approach allows in situ visualization and understanding of the chemical plant defense in real time and paves the way for plant phenotyping for optimized polyphenol secretion.

The filling of single-wall carbon nanotubes (SWCNTs) with dye molecules has become a novel path toadd new functionalities through the mutual interaction of confined dyes and host SWCNTs. In particularcases, the encapsulated dye molecules form strongly interacting molecular arrays and these result inseverely altered optical properties of the dye molecules. Here, we present the encapsulation of a squarainedye inside semiconducting chirality-sorted SWCNTs with diameters ranging from ∼1.15 nm, in whichthe dye molecules can only be encapsulated in a single-file molecular arrangement, up to ∼1.5 nm, inwhich two or three molecular files can fit side-by-side. Through the chirality-selective observation ofenergy transfer from the dye molecules to the surrounding SWCNTs, we find that the absorption wavelengthof the dye follows a peculiar SWCNT diameter dependence, originating from the specific stackingof the dye inside the host SWCNTs. Corroborated by a theoretical model, we find that for each SWCNTdiameter, the dye molecules adopt a close packing geometry, resulting in tunable optical properties ofthe hybrid when selecting a specific SWCNT chirality.

Single-walled carbon nanotubes as emerging quantum-light sources may fill a technological gap in silicon photonics due to their potential use as near-infrared, electrically driven, classical or nonclassical emitters. Unlike in photoluminescence, where nanotubes are excited with light, electrical excitation of single tubes is challenging and heavily influenced by device fabrication, architecture, and biasing conditions. Here we present electroluminescence spectroscopy data of ultra-short-channel devices made from (9,8) carbon nanotubes emitting in the telecom band. Emissions are stable under current biasing, and no enhanced suppression is observed down to 10 nm gap size. Low-temperature electroluminescence spectroscopy data also reported exhibit cold emission and line widths down to 2 meV at 4 K. Electroluminescence excitation maps give evidence that carrier recombination is the mechanism for light generation in short channels. Excitonic and trionic emissions can be switched on and off by gate voltage, and corresponding emission efficiency maps were compiled. Insights are gained into the influence of acoustic phonons on the line width, absence of intensity saturation and exciton-exciton annihilation, environmental effects such as dielectric screening and strain on the emission wavelength, and conditions to suppress hysteresis and establish optimum operation conditions.

Since its discovery ferroelectricity has been an intriguing phenomenon in materials science and is usually observed in a single ferroelectric material. In this study, it is shown that ferroelectriciy can also occur at the interface between two non-ferroelectric materials, a polymer and silicon, and interfacial ferroelectric-like behavior is demonstrated. Sulfonic functional groups on the polymer establish electrochemically switchable dipoles, which are considered to be the origin of ferroelectric polarization and are observed in an atom-thick polar region at the interface. Above room temperature polarization hysteresis loops with long term stability, thermal stability, reliable switching reproducibility and long information retention directly on rigid and flexible silicon substrates are demonstrated. This exotic ferroelectric phenomenon extends polarization switching beyond singular materials and has the potential to advance the design of new ferroelectric devices.

Heterojunctions of carbon nanotubes interfaced with silicon and doped with AuCl3 can achieve attractive power conversion efficiencies when operated in the photovoltaic regime; however, the cost and long-term stability of such devices must be improved before they could become commercially viable. Here, we investigate the role of chemical treatment of the carbon nanotube/silicon interface with either SOCl2 or HNO3, prior to AuCl3 doping, on the stability of the photovoltaic devices. We find that while both treatments initially lead to similar device performance, devices treated with HNO3 are significantly more stable. Using X-ray photoemission spectroscopy, we demonstrate that pretreatment with the powerful organic oxidant SOCl2 generates a variety of low-oxidation-state silicon species at the nanotube–silicon interface that are not generated by exposure to HNO3. These species and their evolution over time are implicated in the reduced device stability, highlighting the importance of silicon oxidation state...

Dead-end filtration has proven to effectively prepare macroscopically (3.8 cm$^2$) aligned thin films from solutionbased single-wall carbon nanotubes (SWCNTs). However, to make this technique broadly applicable, the role of SWCNT length and diameter must be understood. To date, most groups report the alignment of unsorted, large diameter (≈1.4 nm) SWCNTs, but systematic studies on their small diameter are rare (≈0.78 nm). In this work, films with an area of A = 3.81 cm$^2$ and a thickness of ≈40 nm are prepared from length-sorted fractions comprising of small and large diameter SWCNTs, respectively. The alignment is characterized by cross-polarized microscopy, scanning electron microscopy, absorption and Raman spectroscopy. For the longest fractions (L$_{avg}$ = 952 nm ± 431 nm, Δ = 1.58 and L$_{avg}$ = 667 nm ± 246 nm, Δ = 1.55), the 2D order parameter, S2D, values of ≈0.6 and ≈0.76 are reported for the small and large diameter SWCNTs over an area of A = 625 µm$^2$, respectively. A comparison of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory calculations with the aligned domain size is then used to propose a law identifying the required length of a carbon nanotube with a given diameter and zeta potential.

Moir\'e patterns are additional, long-range periodicities in twisted crystalline bilayers. They are known to fundamentally change the electronic states of the layers, but similar effects on their mechanical and vibrational properties have not been discussed so far. Here we show that the Moir\'e potential shifts the radial breathing mode in double walled carbon nanotubes (DWCNTs). The change of frequency is expected to be proportional to the shift in optical transition energies, which are induced by the Moir\'e patterns. To verify our model we performed resonant Raman scattering on purified and sorted semiconducting DWCNTs. We find that the radial breathing mode shifts up to 14 cm$^{-1}$ higher in energy followed by optical transitions energies displacement up to 200 meV to lower energies, compared to the single-walled tubes. We show how to identify the strong coupling condition in DWCNTs from their phonon frequencies and construct a Kataura plot to aid their future experimental assignment., Comment: main script 16 pages, 5 figures; supplementary script 7 pages, 3 figures

The 1D confinement of silicon in the form of a nanowire revives its newness with the emergence of new optical and electronic properties. However, the development of a production process for silicon nanowires (SiNWs) having a high quality crystalline core and exhibiting good stability in solution with effective outer-shell defect passivation is still a challenge. In this work, SiNWs are prepared from a silicon wafer using solution processing steps, and importantly outer-shell-defect passivation is achieved by in situ grafting of organic molecules based on thin films. Defect passivation and the high quality of the SiNWs are confirmed with thin films on glass and flexible plastic substrates. A dramatic enhancement in both the fluorescence lifetime and infrared photoluminescence is observed. The in situ organic passivation of SiNWs has potential application in all low-dimensional silicon devices including infrared detectors, solar cells and lithium-ion battery anodes.

Semiconducting single-wall carbon nanotubes (SWCNTs) fluoresce in the near-infrared (NIR) region, and the emission wavelength depends on their chirality (n,m). Interactions with the environment affect the fluorescence and can be tailored by functionalizing SWCNTs with biopolymers such as DNA, which is the basis for fluorescent biosensors. So far, such biosensors have been mainly assembled from mixtures of SWCNT chiralities with large spectral overlap, which affects sensitivity as well as selectivity and prevents multiplexed sensing. The main challenge to gain chirality-pure sensors has been to combine approaches to isolate specific SWCNTs and generic (bio)functionalization approaches. Here, we created chirality-pure SWCNT-based NIR biosensors for important analytes such as neurotransmitters and investigated the effect of SWCNT chirality/handedness as well as long-term stability and sensitivity. For this purpose, we used aqueous two-phase extraction (ATPE) to gain chirality-pure (6,5)-, (7,5)-, (9,4)-, and (7,6)-SWCNTs (emission at ∼990, 1040, 1115, and 1130 nm, respectively). An exchange of the surfactant sodium deoxycholate (DOC) to specific single-stranded (ss)DNA sequences yielded monochiral sensors for small analytes (dopamine, riboflavin, ascorbic acid, pH). DOC residues impaired sensitivity, and therefore substantial removal was necessary. The assembled monochiral (6,5)-SWCNTs were up to 10 times brighter than their nonpurified counterparts, and the ssDNA sequence determined the absolute fluorescence intensity as well as colloidal (long-term) stability and selectivity for the analytes. (GT)40-(6,5)-SWCNTs displayed the maximum fluorescence response to the neurotransmitter dopamine (+140%, Kd = 1.9 × 10-7 M) and a long-term stability of >14 days. The specific ssDNA sequences imparted selectivity to the analytes mostly independent of SWCNT chirality and handedness of (±) (6,5)-SWCNTs, which allowed a predictable design. Finally, multiple monochiral/single-color SWCNTs were combined to achieve ratiometric/multiplexed sensing of the important analytes dopamine, riboflavin, H2O2, and pH. In summary, we demonstrated the assembly, characteristics, and potential of monochiral (single-color) SWCNTs for NIR fluorescence sensing applications.

Resonant Raman scattering has been used for decades to study single walled carbon nanotubes (CNTs), but lacks a consistent theory that simultaneously explains all characteristic signatures. We argue that a proper description requires introducing exciton polaritons as couples excitonic and photonic states. We describe the polaritons by waveguided theory for a nanometre thick cylinder with modified dielectric function. During their propagation along the tube, the polaritons scatter with phonons and are re-emitted as photons with smaller energy (Stokes scattering event). This approach consistently explains the energetic positions of the Raman resonances for the radial-breathing mode (RBM), the G and the 2D line as well as the asymmetry in the scattering intensity of the incoming and outgoing resonances without resorting to higher-order scattering events. We measured the Raman effect on chirality-sorted nanotubes over the first and second exciton resonance and excellently predict its behaviour, which has not been achieved before. The formation of polaritonic states will affect other optical processes in CNTs. Furthermore, exciton-polariton effects appear inevitable in all one-dimensional excitonic systems, similar to our observations in single walled carbon nanotubes.

The organic passivated CNT/Si solar cell is a new type of low-cost, high-efficiency solar cell, with challenges concerning the stability of the organic layer used for passivation. In this work, the stability of the organic layer is studied with respect to the internal and external (humidity) water content and additionally long-term stability for low moisture environments. It is found that the organic passivated CNT/Si complex interface is not stable, despite both the organic passivation layer and CNTs being stable on their own and is due to the CNTs providing an additional path for water molecules to the interface. With the use of a simple encapsulation, a record power conversion efficiency (PCE) of 22% is achieved and a stable photovoltaic performance is demonstrated. This work provides a new direction for the development of high-performance/lost-cost photovoltaics in the future and will stimulate the use of nanotubes materials for solar cells applications.

Single wall carbon nanotubes (SWCNTs) dispersed by negatively charged sodium deoxycholate (DOC) or positively charged cetrimonium bromide (CTAB) are shown to assemble into aligned films (3.8 cm²) on polycarbonate membranes by slow flow dead-end filtration. Global alignment (S2D max » 0.85) is obtained on both pristine polyvinylpyrrolidone (PVP) coated membranes and those with an intentional 150 nm – 600 nm groove pattern from hot-embossing. In all cases, a custom microfluidic setup capable of precise control and measurement of the volume rate, trans-membrane pressure and the filtration resistance is used to follow SWCNT film formation. Conditions associated with the formation of SWCNT crystallites or their global alignment are identified and these are discussed in terms of membrane fouling and the interaction potential between the surface of the membrane and nanotubes. SWCNT alignment is characterised by cross polarized microscopy, AFM, SEM and Raman spectroscopy. https://doi.org/10.1002/adfm.202107411

The original article has been corrected.

Single wall carbon nanotubes (SWCNTs) dispersed by negatively charged sodium deoxycholate (DOC) or positively charged cetrimonium bromide (CTAB) are shown to assemble into aligned films (3.8 cm$^{2}$) on polycarbonate membranes by slow flow dead-end filtration. Global alignment (S$_{2D max}$≈ 0.85) is obtained on both pristine polyvinylpyrrolidone (PVP) coated membranes and those with an intentional 150–600 nm groove pattern from hot embossing. In all cases, a custom microfluidic setup capable of precise control and measurement of the volume rate, transmembrane pressure, and the filtration resistance is used to follow SWCNT film formation. Conditions associated with the formation of SWCNT crystallites or their global alignment are identified and these are discussed in terms of membrane fouling and the interaction potential between the surface of the membrane and nanotubes. SWCNT alignment is characterized by cross-polarized microscopy, atomic force microscopy, scanning electron microscopy (SEM), and Raman spectroscopy.

The use of carbon nanotubes (CNTs) in photovoltaics could have significant ramifications on the commercial solar cell market. Three interrelated research directions within the field are crucial to the ultimate success of this endeavor; 1) separation, purification, and enrichment of CNTs followed by 2) their integration into organic solar cells as a photosensitive element or 3) in silicon solar cells as a hole selective contact. All three subtopics have experienced tremendous growth over the past 20 years and certainly the performance of the silicon‐based cells is now rapidly approaching that of those on industrial production lines. With a view to these three research areas, the purpose of this Progress Report is to provide a brief overview of each field but more importantly to discuss the challenges and future directions that will allow CNT photovoltaics to move out of the research lab and into end user technology. These include efforts to upscale CNT purification, improvements in power conversion efficiency, increased light absorption, the identification of new material combinations, passivation strategies, and a better understanding of charge separation and energy transfer within these systems.

Widespread use of the polymer extraction method for single-wall carbon nanotubes (SWCNTs) and the ability of endohedral functionalization to alter their material properties make it important to examine the effect of filling on the separation result. Rate-zonal centrifugation is used to obtain empty, water-filled and perfluorooctane-filled large (���1.45 nm), and single-chirality small (���0.78 nm) diameter SWCNTs. These are transferred from water to toluene by dispersion with poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6���-(2,2���-bipyridine))] (PFO-BPy), and absorption and Raman spectroscopy are used to follow the extent of endohedral filling at each step. Measurements are made before and after centrifugation (supernatant) but also in the pellet. PFO-BPy is found to stabilize endohedral-functionalized SWCNTs in the supernatant, but a clear preference for less-filled or empty species is shown. Molecular dynamics simulations are used to model the absorption spectrum of encapsulated water molecules in the PFO-BPy/SWCNT/toluene system and explain why partial water filling is difficult to directly measure. These findings are then used to interpret separation results obtained for raw soot (without intentional filling) and with a view to the low yield of polymer-based SWCNT extraction.

Dielectrophoresis (DEP) describes the motion of suspended objects when exposed to an inhomogeneous electric field. It has been successful as a method for parallel and site-selective assembling of nanotubes from a dispersion into a sophisticated device architecture. Researchers have conducted extensive works to understand the DEP of nanotubes in aqueous ionic surfactant solutions. However, only recently, DEP was applied to polymer-wrapped single-walled carbon nanotubes (SWCNTs) in organic solvents due to the availability of ultra-pure SWCNT content. In this paper, the focus is on the difference between the DEP in aqueous and organic solutions. It starts with an introduction into the DEP of carbon nanotubes (CNT-DEP) to provide a comprehensive, in-depth theoretical background before discussing in detail the experimental procedures and conditions. For academic interests, this work focuses on the CNT-DEP deposition scheme, discusses the importance of the electrical double layer, and employs finite element simulations to optimize CNT-DEP deposition condition with respect to the experimental observation. An important outcome is an understanding of why DEP in organic solvents allows for the deposition and alignment of SWCNTs in low-frequency and even static electric fields, and why the response of semiconducting SWCNTs (s-SWCNTs) is strongly enhanced in non-conducting, weakly polarizable media. Strategies to further improve CNT-DEP for s-SWCNT-relevant applications are given as well. Overall, this work should serve as a practical guideline to select the appropriate setting for effective CNT DEPs.

As narrow optical bandgap materials, semiconducting single-walled carbon nanotubes (SWCNTs) are rarely regarded as charge donors in photoinduced charge-transfer (PCT) reactions. However, the unique band structure and unusual exciton dynamics of SWCNTs add more possibilities to the classical PCT mechanism. In this work, we demonstrate PCT from photoexcited semiconducting (6,5) SWCNTs to a wide-bandgap wrapping poly-[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(6,6′)-(2,2′-bipyridine)] (PFO–BPy) via femtosecond transient absorption spectroscopy. By monitoring the spectral dynamics of the SWCNT polaron, we show that charge transfer from photoexcited SWCNTs to PFO–BPy can be driven not only by the energetically favorable E$_{33}$ transition but also by the energetically unfavorable E$_{22}$ excitation under high pump fluence. This unusual PCT from narrow-bandgap SWCNTs toward a wide-bandgap polymer originates from the up-converted high-energy excitonic state (E$_{33}$ or higher) that is promoted by the Auger recombination of excitons and charge carriers in SWCNTs. These insights provide new pathways for charge separation in SWCNT-based photodetectors and photovoltaic cells.

Semiconducting single wall carbon nanotubes (SWCNTs) fluoresce in the near infrared (NIR) and the emission wavelength depends on their chirality (n,m). Interactions with the environment affect the fluorescence and can be tailored by functionalizing SWCNTs with biopolymers such as DNA, which is the basis for fluorescent biosensors. So far, such biosensors were mainly assembled from mixtures of SWCNT chiralities with large spectral overlap, which affects sensitivity as well as selectivity and prevents multiplexed sensing. The main challenge to gain chirality pure sensors has been to combine approaches to isolate specific SWCNTs and generic (bio)functionalization approaches. Here, we created chirality pure SWCNT-based NIR biosensors for important analytes such as neurotransmitters and investigated the impact of SWCNT chirality/handedness as well as long-term stability and sensitivity. For this purpose, we used aqueous two-phase extraction (ATPE) to gain chirality pure (6,5)-, (7,5)-, (9,4)- and (7,6)- SWCNTs (emission at ~ 990, 1040, 1115 and 1130 nm). Exchange of the surfactant sodium deoxycholate (DOC) to specific singlestranded (ss)DNA sequences yielded monochiral sensors for small analytes (dopamine, riboflavin, ascorbic acid, pH). DOC used in the separation process was completely removed because residues impaired sensing. The assembled monochiral sensors were up to 10 times brighter than their non-purified counterparts and the ssDNA sequence affected absolute fluorescence intensity as well as colloidal (long-term) stability and selectivity for the analytes. (GT)40-(6,5)-SWCNTs displayed the maximum fluorescence response to the neurotransmitter dopamine (+140 %, Kd = 1.9 x10-7 M) and a long-term stability > 14 days. Furthermore, the specific ssDNA sequences imparted selectivity to the analytes independent of SWCNT chirality and handedness of (+/-) (6,5)-SWCNTs. These monochiral/single-color SWCNTs enabled ratiometric/multiplexed sensing of dopamine, riboflavin, H2O2 and pH. In summary, we demonstrated the assembly, characteristics and potential of monochiral (single-color) SWCNTs for multiple NIR fluorescent sensing applications.

In the past, the application of carbon nanotube-silicon solar cell technology to industry has been limited by the use of a metallic frame to define the active area in the middle of a silicon wafer. In our work, we use industry standard device geometries with a front- and back-junction design which allow for the entire wafer to be used as the active area. These are enabled by the use of an intermixed Nafion layer which simultaneously acts a passivation, antireflective and physical blocking layer as well as a nanotube dopant. This leads to the formation of a hybrid nanotube/Nafion passivated charge selective contact (PCSC) and solar cells with active areas of 1 – 16 cm2 are fabricated. Record maximum power conversion efficiencies of 15.2% and 18.9% are reported for front- and back-junction devices for 1 cm2 and 3 cm2 active areas, respectively. By placing the nanotube film on the rear of the device in a back-junction architecture many of the design related challenges for carbon nanotube silicon solar cells are addressed and their future application to industrialized processes are discussed. Additionally, traditional silicon solar cells extract holes and achieve interface passivation with the use of a boron dopant and dielectric thin films such as silicon oxide or hydrogenated amorphous silicon. Without these two key components, few technologies have realized power conversion efficiencies above 20%. We now develop a carbon nanotube/Nafion ink that can be spin coated directly onto a silicon wafer to serve simultaneously as a hole extraction layer, but also to passivate interfacial defects. This enables a low-cost fabrication process that is absent of vacuum equipment and high-temperatures. Power conversion efficiencies of 21.4% on an device area of 4.8 cm2 and 20% on an industrial size (245.71 cm2) wafer are obtained. [1] D. D. Tune, N. Mallik, H. Fornasier, B. S. Flavel, Adv. Energy Mater. 10, 2020, 1903261. DOI: 10.1002/aenm.201903261 [2] J. Chen, D. D. Tune, K. Ge, H. Li, B. S. Flavel, Adv. Funct. Mater. 2020, 30 2000484. DOI: 10.1002/adfm.202000484 [3] J. Chen, L. Wan, H. Li, J. Yan, J. Ma, B. Sun, F. Li, B. S. Flavel, Adv. Funct. Mater. 30, 2020, 202004476. DOI: 10.1002/adfm.202004476 [4] L. Wieland, H. Li, C. Rust, J. Chen, B. S. Flavel, Adv. Energy Mater. 2020 just accepted manuscript. DOI: 10.1002/aenm.202002880 Figure 1

Semiconducting single wall carbon nanotubes (SWCNTs) fluoresce in the near infrared (NIR) and the emission wavelength depends on their chirality (n,m). Interactions with the environment affect the fluorescence and can be tailored by functionalizing SWCNTs with biopolymers such as DNA, which is the basis for fluorescent biosensors. So far, such biosensors were mainly assembled from mixtures of SWCNT chiralities with large spectral overlap, which affects sensitivity as well as selectivity and prevents multiplexed sensing. The main challenge to gain chirality pure sensors has been to combine approaches to isolate specific SWCNTs and generic (bio)functionalization approaches. Here, we created chirality pure SWCNT-based NIR biosensors for important analytes such as neurotransmitters and investigated the impact of SWCNT chirality/handedness as well as long-term stability and sensitivity. For this purpose, we used aqueous two-phase extraction (ATPE) to gain chirality pure (6,5)-, (7,5)-, (9,4)- and (7,6)-SWCNTs (emission at ~ 990, 1040, 1115 and 1130 nm). Exchange of the surfactant sodium deoxycholate (DOC) to specific single-stranded (ss)DNA sequences yielded monochiral sensors for small analytes (dopamine, riboflavin, ascorbic acid, pH). DOC residues impaired sensitivity and therefore sufficient removal was necessary. The assembled monochiral sensors were up to 10 times brighter than their non-purified counterparts and the ssDNA sequence determined absolute fluorescence intensity as well as colloidal (long-term) stability and selectivity for the analytes. (GT)40-(6,5)-SWCNTs displayed the maximum fluorescence response to the neurotransmitter dopamine (+140 %, Kd = 1.9 x10-7 M) and a long-term stability > 14 days. The specific ssDNA sequences imparted selectivity to the analytes in majority of the cases independent of SWCNT chirality and handedness of (+/-) (6,5)-SWCNTs, which allows a predictable design. Finally, multiple monochiral/single-color SWCNTs were combined to achieve ratiometric/multiplexed sensing of the important analytes dopamine, riboflavin, H2O2 and pH. In summary, we demonstrated the assembly, characteristics and potential of monochiral (single-color) SWCNTs for multiple NIR fluorescent sensing applications.

Carbon nanotubes (CNTs) are a 1D dimensional material with anisotropy in their thermal, electronic and optical properties. It is therefore a grand challenge to control their orientation in an ensemble and prepare large scale aligned thin-films. In this direction, slow flow dead-end filtration using polyvinylpyrrolidone-coated polycarbonate membranes has recently been shown to achieve global alignment of CNTs across an entire membrane. This route is highly attractive because it allows for purified dispersions to be used but it has proven to be difficult to reproduce. In this work, we present a custom dead-end filtration setup capable of precise in-situ measurement of flow, trans-membrane pressure and effective retention. This setup allows us to identify the important variables to achieve global alignment and explain why others have found it hard to reproduce in their own laboratory.

Double walled carbon nanotubes (DWCNT) are formed from two concentric single walled carbon nanotubes. They are a one-dimensional moiré system where the coupling strength between the two walls varies greatly depending on the atomic structure of the two tubes. In this talk we discuss the effect of moiré coupling on the electronic and vibrational states of DWCNTs. We focus on the regime of strong moiré coupling and the combination of semiconducting inner and semiconducting outer tube. For such DWCNTs moiré coupling leads to a red-shift of most optical transition energies. The coupling also affects the frequency of the radial breathing mode (RBM), which is an unexpected finding in connection with moiré interaction. We predict a linear correlation between the change in RBM frequency and in optical transition energy. To verify our predictions we will present resonant Raman experiments on DWCNTs sorted by metallic character. We show that the splitting of the RBM frequencies in DWCNT samples is a clear manifestation of the moiré coupling and construct a Kataura plot for the assignment of double walled tubes. Using resonance Raman profiles of the RBM we confirm the correlation between electronic and vibrational shifts. We also discuss the effect of dielectric screening on the Raman intensities. Our work shows how moiré coupling can strongly affect the vibrational in addition to the electronic and optical states of a one-dimensional system.

Ultrahigh purity semiconducting single-walled carbon nanotubes (S-SWCNTs) are required for high-performance transistors. Aqueous two-phase (ATP) separation is an attractive method to obtain such SWCNTs due to its simplicity and scalability. This work targeted two questions; namely what is the upper limit of S-SWCNT purity that can be achieved by multiple cycles of ATP separation from the most commonly used polyethylene glycol and dextran system and how accurately can commonly used methods characterize the improvement in purity? SWCNT purity in nanotube dispersions obtained by multi-cycle ATP separation (2, 4, 6 and 8 cycles) was evaluated by three methods, including UV-vis-NIR absorption spectroscopy analysis, performance of thin-film field effect transistors (FETs) prepared by drop casting and short-channel FET devices prepared by dielectrophoresis deposition. Absorption spectroscopic analysis and the performance of the thin-film FET devices can hardly differentiate metallic SWCNT residues in the dispersions obtained after 4 cycles with the purity above 99.5%, and the short channel FET devices prepared by dielectrophoresis deposition are more sensitive towards tiny metallic SWCNT residues. A new method was also demonstrated to visualize the minor metallic content in the nanotube suspension using voltage contrast imaging in a scanning electron microscope, which enables rapid screening of many devices and the accurate obtainment of metallic content without performing a large number of individual transconductance measurements.

Monochiral (7,5) single walled carbon nanotubes (SWCNTs) are integrated into a field effect transistor device in which the built-in electric field at the nanotube/metal contact allows for exciton separation under illumination. Variable wavelength spectroscopy and 2D surface mapping of devices consisting of 10–20 nanotubes are performed in the visible region and a strong correlation between the nanotube's second optical transition (S22) and the photocurrent is found. After integration, the SWCNTs are non-covalently modified with three different fluorescent dye molecules with off-resonant absorption maxima at 532 nm, 565 nm, and 610 nm. The dyes extend the absorption properties of the nanotube and contribute to the photocurrent. This approach holds promise for the development of photo-detectors and for applications in photovoltaics and biosensing.

Selective dispersion of semiconducting single-walled carbon nanotube (SWCNTs) with conjugated polymers typically involves harsh sonication methods that damage and shorten the nanotubes. Here, we use simple high speed shear force mixing (SFM) to disperse nearly monochiral (6,5) SWCNTs with poly[(9,9-dioctylfluorenyl-2,7-diyl)- alt - co -(6,6′-{2,2′-bipyridine})] (PFO-BPy) in toluene with high yield and in large volumes. This highly scalable process disperses SWCNTs of exceptional quality with an average tube length of 1.82 μm and an ensemble photoluminescence quantum yield (PLQY) of 2.3%. For the first time for SWCNTs, we describe and apply absolute PLQY measurements, without the need for any reference emitter. We directly compare values for average SWCNT length, PLQY, linewidth and Stokes shift to other dispersion methods, including bath and tip sonication, as well as other sorting methods such as gel chromatography. We find that SFM results in dispersions of longer SWCNT with higher average PLQY than any other technique, thus making it an ideal method for sorting large amounts of long, high quality and purely semiconducting SWCNTs.