Polymer-free semiconducting carbon nanotube networks demonstrate unprecedented equivalent n- and p-type thermoelectric performance.
Capping perovskite absorber layers with semiconducting carbon nanotubes enables sub-picosecond hole extraction and recombination times of hundreds of microseconds.
Materials with switchable absorption properties have been widely used for smart window applications to reduce energy consumption and enhance occupant comfort in buildings. In this work, we combine the benefits of smart windows with energy conversion by producing a photovoltaic device with a switchable absorber layer that dynamically responds to sunlight. Upon illumination, photothermal heating switches the absorber layer—composed of a metal halide perovskite-methylamine complex—from a transparent state (68% visible transmittance) to an absorbing, photovoltaic colored state (less than 3% visible transmittance) due to dissociation of methylamine. After cooling, the methylamine complex is re-formed, returning the absorber layer to the transparent state in which the device acts as a window to visible light. The thermodynamics of switching and performance of the device are described. This work validates a photovoltaic window technology that circumvents the fundamental tradeoff between efficient solar conversion and high visible light transmittance that limits conventional semitransparent PV window designs.
Single-walled carbon nanotubes (SWCNTs) are attractive materials for next-generation energy-harvesting technologies, including thermoelectric generators, due to their tunable opto-electronic properties and high charge carrier mobilities. Controlling the Fermi level within these unique 1D nanomaterials is often afforded by charge transfer interactions between SWCNTs and electron or hole accepting species. Conventional methods to dope SWCNT networks typically involve the diffusion of molecular redox dopant species into solid-state thin films, but solution-phase doping could potentially provide routes and/or benefits for charge carrier transport, scalability, and stability. Here, we develop a methodology for solution-phase doping of polymer-wrapped, highly enriched semiconducting SWCNTs using a p-type charge transfer dopant, F4TCNQ. This allows doped SWCNT inks to be cast into thin films without the need for additional post-deposition doping treatments. We demonstrate that the introduction of the dopant at varying stages of the SWCNT dispersion process impacts the ultimate thermoelectric performance and observe that the dopant alters the polymer selectivity for semiconducting vs metallic SWCNTs. In contrast to dense semiconducting polymer films, where solution-phase doping typically leads to disrupted morphologies and poorer TE performance than solid-state doping, thin films of solution-doped s-SWCNTs perform similarly to their solid-state doped counterparts. Interestingly, our results also suggest that solution-phase F4TCNQ doping leads to fully ionized and dimerized F4TCNQ anions in solid-state films that are not observed in films doped with F4TCNQ after deposition. Our results provide a framework for the application of solution-phase doping to a broad array of high-performance SWCNT-based thermoelectric materials and devices that may require high-throughput deposition techniques.
The SARS-CoV-2 infection has caused a pandemic with a case rate of over 290 000 lab-confirmed cases and over 40 000 deaths in the UK. There is little evidence to inform the optimal management of a patient presenting with new or relapsed acute idiopathic thrombocytopaenic purpura with concurrent SARS-CoV-2 infection. We present a case of severe thrombocytopaenia complicated by subdural haematoma and rectal bleed associated with COVID-19. A 67-year-old man, admitted with a non-productive cough and confusion, was found to be positive for COVID-19. Ten days after admission, his platelets decreased from 146×109/L to 2×109/L. His platelets did not increase despite receiving frequent platelet transfusions. He was non-responsive to corticosteroids and intravenous immunoglobulins. Romiplostim and eltrombopag were given and after 9 weeks of treatment, his platelet count normalised. He was deemed medically fit with outpatient follow-up in a haematology clinic.
Single-walled carbon nanotubes (SWCNTs) have the potential to revolutionize many areas of opto-electronics, particularly thin-film photovoltaics and thermoelectrics due to their high carrier mobility and low-dimensional structure. Much effort has been devoted to increasing the thermoelectric power factor of SWCNTs by controlling the doping levels and doping types for enhanced thermoelectric conversion. Controlling the Fermi energy level within these unique 1D structures is often afforded by charge transfer interactions between host species (SWCNT) and electron or hole accepting species (dopant). Recent advancement of polymer-wrapped SWCNTs allows for thin-films of SWCNTs to be to cast using solution-based processing techniques. Conventional methods to dope SWCNTs rely upon intercalation of dopant molecules within solid-state networks of SWCNTs in a thin film. Here, we discuss methods to dope polymer-wrapped SWCNTs directly in solution by adding a p-type charge transfer dopant, F4-TCNQ, to SWCNT dispersions prior to thin-film deposition. This approach provides more control and reproducibility of the doping level and allows for SWCNTs inks to directly create doped thin films without the need for post-deposition treatments. Interestingly, we show that introduction of the dopant at varying stages of polymer wrapping process of SWCNT dispersion impacts the polymer selectivity for semiconducting vs. metallic SWCNTs. By controlling the dopant concentration in solution, we show that the degree of doping is retained upon thin film formation, enabling creation of SWCNT thin films with controllable carrier concentrations for opto-electronic applications. We characterize the thermoelectric properties of the solution-phase doped films, and demonstrate large, tunable power factors that correlate well with the degree of doping in both the solution- and solid-state. Additionally, I will briefly discuss the implications of these results on the chemical interaction of F4-TCNQ with SWCNTs of various band gaps. This work has implications in the improvement of SWCNT-based thermoelectric devices and capability to create doped SWCNT thin films directly from solution for use in other opto-electronic applications such as thin-film photovoltaics.
The optical and electrical properties of single-walled carbon nanotubes (SWCNTs) make them attractive for a number of energy conversion devices, including thin-film photovoltaics and thermoelectrics. Both fundamental studies and device efficiencies have benefited from the ability to selectively extract semiconducting SWCNTs (s-SWCNTs) with high yield, purity, and throughput with pi-congujated semiconducting polymers such as polyfluorenes. However, it has proven to be challenging to quantitatively remove these polymers after selective extraction of s-SWCNTs, so thin films prepared from polyfluorene-based dispersions typically have significant amounts of residual polymer. Since charge and exciton transport within s-SWCNT thin films can be sensitive to the degree of inter-nanotube electronic coupling, the ultimate effects of this residual polymer on transport are unclear although they are likely to be deleterious. A number of polymers have recently emerged that can be decomposed into monomers after selective extraction of s-SWCNTs, enabling thin s-SWCNT film fabrication in the complete absence of residual wrapping polymer. In this presentation, I will discuss our recent results demonstrating large improvements to transport for films that are prepared with a removable polymer. These improvements translate directly into improved performance for a variety of thin-film devices based on s-SWCNTs.
There is a growing interest in the use of carbon nanostructures for a variety of electronic and optoelectronic technologies, including energy harvesting applications such as photovoltaics (PV) and thermoelectrics (TE). We will present a series of studies aimed at improving the TE performance of semiconducting single-walled carbon nanotube (s-SWCNT) thin film networks. The optical and electrical performance of SWCNT ensembles is often limited by the presence of metallic single-walled carbon nanotube (m-SWCNT). We will demonstrate a polymer-based purification strategy that effectively eliminates these, and other impurities, from the raw material, leaving s-SWCNTs in extremely high purity. Modification of this extraction process produces s-SWCNT thin film networks where the polymer can be completely removed, resulting in close tube-tube contacts in a dense s-SWCNT network. Removal of the polymer in the solid state, rather than in solution, also minimizes nanotube bundling during network formation. By controlling the bundle size and extent of polymer remaining in the s-SWCNT network we demonstrate TE power factors that almost double the performance of s-SWCNT networks previously demonstrated. We trace the improved performance to an enhanced electrical conductivity, resulting from improved doping and strongly enhanced charge carrier mobility, and analyze our data within the framework of a recently developed thermoelectric transport model. Finally, we demonstrate that the removal of the polymer from the s-SWCNT network has negligible impact on the thermal conductivity, which appears to be limited by dopant-induced phonon scattering processes. These observations demonstrate the ability to exert exquisite control of the thermoelectric performance by controlling the composition of the s-SWCNT network and tuning the carrier density (i.e., Fermi energy), and touts SWCNTs as an avenue for realizing thermally stable room temperature thermoelectric devices fashioned from inexpensive and abundant organic constituents.
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