Hybrid organic-inorganic perovskite solar cells (PSCs) have drawn great attention in the past decade due to the rapid growth of their power conversion efficiency (PCE) and the advantage of their ...low-cost fabrication. The hole-transport materials (HTMs) play a crucial role in achieving high efficiency and operational stability of PSCs. In this work, we report the synthesis of two novel conjugated polymers by coupling of the alkylsilyl-substituted benzo1,2-
b
:4,5-
b
′dithiophene unit with the thiophene-bridged pyrazine block and their investigation as dopant-free HTMs in n-i-p PSCs. The devices with polymer
PBPyT-ex
(poly(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo1,2-
b
:4,5-
b
′dithiophene)-
alt
-5,5′-(2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine)) demonstrate PCEs up to 17.5%, outperforming the 14.9% efficiency of PSCs with
PBPyT-in
(poly(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo1,2-
b
:4,5-
b
′dithiophene)-
alt
-5,5′-(2,5-bis(3-(2-ethylhexyl)thiophen-2-yl)pyrazine)), which is attributed to the difference in the quality of HTM films. The results obtained feature the combination of pyrazine, thiophene and benzodithiophene units as a successful example of polymeric HTM backbone design for PSCs with encouraging efficiency and high operational stability over 1500 h under continuous illumination.
Pyrazine-based conjugated polymers are shown as promising hole-transport materials for perovskite solar cells with encouraging efficiency and high operational stability.
In this work we report on modification of electrical and optical properties of extended thin films of single-wall carbon nanotubes induced by iodination from gaseous phase. High resolution ...transmission electron microscopy and Raman data have revealed formation of different types of polyiodide species or one-dimensional iodine crystals (depending on pristine nanotube geometry) inside nanotubes. UV–vis–NIR optical absorption spectra of iodinated nanotubes demonstrated a clear suppression of the optical absorption band corresponding to the first electron transition for semiconducting nanotubes (with the factor determined by the nanotube geometry). It was interpreted as a result of charge transfer from nanotubes to polyiodide species formed inside them. Because of this effect the Fermi level shifted down into the valence band, and the nanotube conductivity type was changed. For filled nanotube films the metallic type of temperature-dependent electrical resistance behavior was observed at elevated temperatures. A reduction of the electrical resistance of pristine films by an order of magnitude (from 1550Ohm/sq to 270Ohm/sq; from 865Ohm/sq to 150Ohm/sq; from 700Ohm/sq to 70Ohm/sq at 300K) has been observed. The obtained sheet resistances are comparable with those for the most popular today material for transparent conductive electrodes – indium tin oxide.
The nonlinear absorption and refraction of free-standing films made of single-walled carbon nanotubes (SWNTs) have been investigated experimentally and theoretically. By solving the quantum kinetic ...equations that take into account both the intra- and interband transitions, we obtain the analytical expression for the SWNT nonlinear conductivity. The nonlinear absorption coefficient and saturation intensity of the film comprising randomly orientated SWNTs have been calculated in a broad spectral range spanning over M11, S11, and S22 absorption bands. The effects of the laser pulse duration and dynamic Burstein−Moss shift on the saturation intensity have been revealed. We demonstrate in the experiment that, under irradiation with femtosecond laser pulses, the absorption modulation depth of SWNT film at resonance wavelength 1375 nm is as high as 30%. The observed saturation intensity minimum is red-shifted with respect to the absorption maximum due to the dynamic Burstein−Moss shift. The saturation intensity within the S22 band is 26−fold lower than that out of the band at 795 nm. The closed-aperture z-scan measurements reveal the negative nonlinear refractive index n2 = −3.1 × 10−12 cm2/W at 795 nm.
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In this paper, we explore the possibility of using free-standing thin films from single-walled carbon nanotube (SWCNT) material in optics of the extreme ultraviolet (EUV) range. Test samples were ...fabricated using an aerosol chemical vapor deposition method. Synchrotron radiation was used to record the transmittance spectra of samples in the EUV range. The measured transmittance for a film 40 nm thick almost monotonously increases from 76% at a wavelength of 20 nm–99% at a wavelength of 1 nm. The measured stress-strain curve for the test samples shows that the SWCNT-based thin films have rather high ductility as opposite to fragile films made of conventional solid state materials. We use numerical simulations to demonstrate that the film strain occurs mainly by straightening and sliding of the nanotubes past each other without forming of strain localization responsible for fragile behavior. The combination of high radiation transmittance and unique mechanical properties makes the SWCNT-based thin films very promising for use in the EUV optics. In particular, such films can be used to protect delicate optical elements for EUV lithography from their contamination with debris particles.
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We measure the conductivity spectra of thin films comprising bundled single-walled carbon nanotubes (CNTs) of different average lengths in the frequency range 0.3-1000 THz and temperature interval ...10-530 K. The observed temperature-induced changes in the terahertz conductivity spectra are shown to depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which we obtain from Drude fits of the measured conductivity in the range 0.3-2 THz for 10 μm length CNTs. This increasing scattering rate with temperature results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS2 nanotubes and CNTs versus CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak.
Flexible optoelectronic structures are required in a wide range of applications. Large scale modified silicone-embedded n-GaP nanowire arrays of a record 6 µm thin membranes were studied. A ...homogeneous silicone encapsulation was enabled by G-coating using a heavy-load centrifuge. The synthesized graft-copolymers of polydimethylsiloxane (PDMS) and polystyrene demonstrated two times lower adhesion to Si compared to standard PDMS, allowing 3 square inch area high quality silicone/nanowire membrane mechanical release, preserving the growth Si substrate for a further re-use after chemical cleaning. The 90% transparent single-walled carbon nanotubes electrical contacts to the embedded n-GaP nanowires demonstrated mechanical and electrical stability. The presented methods can be used for the fabrication of large scale flexible inorganic optoelectronic devices.
Electrical transport mechanisms of 2D carbon nanotube networks are presently under intensive studies. The related experimental data are ambiguous and controversial. We report on terahertz-infrared ...spectra of optical conductivity and dielectric permittivity of thin transparent films composed of pristine and CuCl- or iodine-doped single-walled carbon nanotubes (SWCNTs) measured in the frequency range from 7 to 25 000 cm−1 and at temperatures from 5 to 300 K. Controversially to the existing results, we have not observed a clear signature of the so-called terahertz conductivity peak. Instead, a typical metallic-like frequency- and temperature-dependent behavior of the conductivity and permittivity has been discovered. It was attributed to the high quality interconnected SWCNT network providing the almost free pathways for charge carriers. Applying Drude conductivity model, we have determined the temperature and doping dependences of effective parameters of the carriers in the films: plasma frequency, scattering rate, mobility, mean-free path. The obtained results demonstrate a great potential of the material in the field of electromagnetic applications at frequencies up to few terahertz.
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Abstract
Nonlocal quasiparticle transport in normal-superconductor-normal (NSN) hybrid structures probes sub-gap states in the proximity region and is especially attractive in the context of Majorana ...research. Conductance measurement provides only partial information about nonlocal response composed from both electron-like and hole-like quasiparticle excitations. In this work, we show how a nonlocal shot noise measurement delivers a missing puzzle piece in NSN InAs nanowire-based devices. We demonstrate that in a trivial superconducting phase quasiparticle response is practically charge-neutral, dominated by the heat transport component with a thermal conductance being on the order of conductance quantum. This is qualitatively explained by numerous Andreev reflections of a diffusing quasiparticle, that makes its charge completely uncertain. Consistently, strong fluctuations and sign reversal are observed in the sub-gap nonlocal conductance, including occasional Andreev rectification signals. Our results prove conductance and noise as complementary measurements to characterize quasiparticle transport in superconducting proximity devices.
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