Zakhidov, Anvar A.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3178
Anvar Zakhidov is a professor of physics and a co-founder and Associate Director of the Alan G. MacDiarmid NanoTech Institute. Professor Zakhidov's main research fields are:
- Advanced Materials: Photonic Crystals, Nanostructured thermoelectrics. Carbon nanotubes and fullerenes. Nanotechnology: self-assembly, micro-templating
- Optoelectronics of organic & molecular solids: photocells, molecular electronic devices, OLEDs
- Spectroscopy of molecular crystals, conducting polymers, fullerenes, charge-transfer complexes, and organic ferromagnets
- MW spectroscopy of high-temperature, organic and fulleride superconductors
- Theory of low-dimensional organic solids, conducting polymers and fullerenes: properties of electronic excitations: excitons, polarons/bipolarons, solitons
Learn more about Dr. Zakhidov's research on his Faculty, NanoTech Institute, and Research Explorer pages.
News
Elected 2020 fellow of the American Association for the Advancement of Science (AAAS) "for creative, pioneering contributions to the design, processing and understanding of functional nanomaterials, including carbon nanotubes, fullerenes and perovskites."
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Recent Submissions
Item A Few-Minute Synthesis of CsPbBr₃ Nanolasers with a High Quality Factor by Spraying at Ambient Conditions(Amer Chemical Soc, 2018-12-12) Pushkarev, Anatoly P.; Korolev, Viacheslav, I.; Markina, Daria, I.; Komissarenko, Filipp E.; Naujokaitis, Arnas; Drabavicius, Audrius; Pakstas, Vidas; Franckevicius, Marius; Khubezhov, Soslan A.; Sannikov, Denis A.; Zasedatelev, Anton, V.; Lagoudakis, Pavlos G.; Zakhidov, Anvar A.; Makarov, Sergey, V.; 0000-0003-3983-2229 (Zakhidov, AA); Zakhidov, Anvar A.Inorganic cesium lead halide perovskite nanowires, generating laser emission in the broad spectral range at room temperature and low threshold, have become powerful tools for the cutting-edge applications in the optoelectronics and nanophotonics. However, to achieve high-quality nanowires with the outstanding optical properties, it was necessary to employ long-lasting and costly methods of their synthesis, as well as postsynthetic separation and transfer procedures that are not convenient for large-scale production. Here we report a novel approach to fabricate high quality CsPbBr₃ nanolasers obtained by rapid precipitation from dimethyl sulfoxide solution sprayed onto hydrophobic substrates at ambient conditions. The synthesis technique allows producing the well-separated nanowires with a broad size distribution of 2-50 μm in 5-7 min, being the fastest method to the best of our knowledge. The formation of nanowires occurs via ligand-assisted reprecipitation triggered by intermolecular proton transfer from (CH₃)₂CHOH to H₂O in the presence of a minor amount of water. The XRD patterns confirm an orthorhombic crystal structure of the as-grown CsPbBr₃ single nanowires. Scanning electron microscopy images reveal their regular shape and truncated pyramidal end facets, while high-resolution transmission electron microscopy ones demonstrate their single-crystal structure. The lifetime of excitonic emission of the nanowires is found to be 7 ns, when the samples are excited with energy below the lasing threshold, manifesting the low concentration of defect states. The measured nanolasers of different lengths exhibit pronounced stimulated emission above 13 μJ cm⁻² excitation threshold with quality factor Q = 1017-6166. Their high performance is assumed to be related to their monocrystalline structure, low concentration of defect states, and improved end facet reflectivity.Item Beyond Quantum Confinement: Excitonic Nonlocality in Halide Perovskite Nanoparticles with Mie Resonances(Royal Society of Chemistry) Berestennikov, A. S.; Li, Y.; Iorsh, I. V.; Zakhidov, Anvar A.; Rogach, A. L.; Makarov, S. V.; Zakhidov, Anvar A.Halide perovskite nanoparticles have demonstrated pronounced quantum confinement properties for nanometer-scale sizes and strong Mie resonances for 10 2 nm sizes. Here we studied the intermediate sizes where the nonlocal response of the exciton affects the spectral properties of Mie modes. The mechanism of this effect is associated with the fact that excitons in nanoparticles have an additional kinetic energy that is proportional to k 2 , where k is the wavenumber. Therefore, they possess higher energy than in the case of static excitons. The obtained experimental and theoretical results for MAPbBr 3 nanoparticles of various sizes (2-200 nm) show that for particle radii comparable with the Bohr radius of the exciton (a few nanometers in perovskites), the blue-shift of the photoluminescence, scattering, and absorption cross-section peaks related to quantum confinement should be dominating due to the weakness of Mie resonances for such small sizes. On the other hand, for larger sizes (more than 50-100 nm), the influence of Mie modes increases, and the blue shift remains despite the fact that the effect of quantum confinement becomes much weaker. ©2019 The Royal Society of Chemistry.Item Resonant Silicon Nanoparticles for Enhanced Light Harvesting in Halide Perovskite Solar Cells(Wiley-VCH Verlag) Furasova, A.; Calabró, E.; Lamanna, E.; Tiguntseva, E.; Ushakova, E.; Ubyivovk, E.; Mikhailovskii, V.; Zakhidov, Anvar A.; Makarov, S.; Di Carlo, A.; Zakhidov, Anvar A.Implementation of resonant nanoparticles (NPs) for improving performance of organometal halide perovskites solar cells is highly prospective approach, because it is compatible with the solution processing techniques used for any organic materials. Previously, resonant metallic NPs have been incorporated into perovskite solar cells for better light absorption and charge separation. However, high inherent optical losses and high reactivity of noble metals with halides in perovskites are main limiting factors for this approach. Incidentally, low-loss and chemically inert resonant silicon NPs allow for light trapping and enhancement at nanoscale, being suitable for thin film photovoltaics. Here photocurrent and fill-factor (FF) enhancements in meso-superstructured perovskite solar cells, incorporating resonant silicon NPs between mesoporous TiO₂ transport and active layers, are demonstrated. This results in a boost of device efficiency up to 18.8% and FF up to 79%, being a record among the previously reported values on NPs incorporation into CH₃NH₃PbI₃ perovskite-based solar cells. Theoretical modeling and optical characterization reveal the significant role of Si NPs for increased light absorption in the active layer rather than for better charge separation. The proposed strategy is universal and can be applied in perovskite solar cells with various compositions, as well as in other optoelectronic devices. ©2018 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles(American Chemical Society) Tiguntseva, E. Y.; Baranov, D. G.; Pushkarev, A. P.; Munkhbat, B.; Komissarenko, F.; Franckevičius, M.; Zakhidov, Anvar A.; Shegai, T.; Kivshar, Y. S.; Makarov, S. V.; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Zakhidov, Anvar A.Halide perovskites are known to support excitons at room temperatures with high quantum yield of luminescence that make them attractive for all-dielectric resonant nanophotonics and meta-optics. Here we report the observation of broadly tunable Fano resonances in halide perovskite nanoparticles originating from the coupling of excitons to the Mie resonances excited in the nanoparticles. Signatures of the photon-exciton ("hybrid") Fano resonances are observed in dark-field spectra of isolated nanoparticles, and also in the extinction spectra of aperiodic lattices of such nanoparticles. In the latter case, chemical tunability of the exciton resonance allows reversible tuning of the Fano resonance across the 100 nm bandwidth in the visible frequency range, providing a novel approach to control optical properties of perovskite nanostructures. The proposed method of chemical tuning paves the way to an efficient control of emission properties of on-chip-integrated light-emitting nanoantennas. © 2018 American Chemical Society.Item Room Temperature Operation of Directly Patterned Perovskite Distributed Feedback Light Source under Continuous-Wave Optical Pumping(Institute of Electrical and Electronics Engineers Inc.) Gharajeh, Abouzar; Haroldson, Ross; Li, Zhitong; Moon, Jiyoung; Balachandran, Balasubramaniam; Hu, Wenchuang (Walter); Zakhidov, Anvar A.; Gu, Qing; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); 0000-0003-3855-3690 (Gu, Q); Gharajeh, Abouzar; Haroldson, Ross; Li, Zhitong; Moon, Jiyoung; Balachandran, Balasubramaniam; Hu, Wenchuang (Walter); Zakhidov, Anvar A.; Gu, QingWe report the first directly patterned perovskite distributed feedback (DFB) resonator with a narrow amplified spontaneous emission (ASE) at pump powers as low as 0.1W/cm², under continuous-wave (CW) optical pumping condition at room temperature.Item Photoinduced Migration of Ions in Optically Resonant Perovskite Nanoparticles(Pleiades Publishing) Gets, D. S.; Tiguntseva, E. Y.; Berestennikov, A. S.; Lyashenko, T. G.; Pushkarev, A. P.; Makarov, S. V.; Zakhidov, Anvar A.; Zakhidov, Anvar A.Organic–inorganic perovskites with a mixed anion composition are widely used in solar cells, light-emitting diodes, and nanophotonic structures. Light nanosources based on resonant perovskite nanoparticles are of particular interest. However, perovskites with such a composition demonstrate the light-induced segregation of anions, which leads to a reversible dynamic rearrangement of the optical properties of a material and photoluminescence spectra. In this work, the photoinduced process of change in optical properties in resonant hybrid perovskite nanoparticles with a mixed anion composition (MAPbBr₁.₅I₁.₅, where MA = NH₃CH₃⁺) has been studied. Comparison with a similar process in a perovskite thin film with a similar composition has shown that the photoinduced migration of halogen ions in a nanoparticle occurs cyclically. This is due to the competition of two processes: the concentration of ions near the boundaries of the particle and migration caused by the gradient of the density of light-generated electron–hole pairs. This effect in resonant nanoparticles makes it possible to obtain optically tunable nanoantennas.Item Halide-Perovskite Resonant Nanophotonics(Wiley-vch Verlag) Makarov, S.; Furasova, A.; Tiguntseva, E.; Hemmetter, A.; Berestennikov, A.; Pushkarev, A.; Zakhidov, Anvar A.; Kivshar, Y.; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Zakhidov, Anvar A.Halide perovskites have emerged recently as promising materials for many applications in photovoltaics and optoelectronics. Recent studies of optical properties of halide perovskites suggest many novel opportunities for a design of advanced nanophotonic devices due to their low-cost fabrication, relatively high values of the refractive index, existence of excitons at room temperatures, broadband bandgap tunability, high optical gain, and strong nonlinear response, as well as simplicity of their integration with other types of optical and electronic structures. This paper provides an overview of the recent progress in the study of optical effects originating from nanostructured perovskites, and it also oversees a range of potential applications of resonant nanophotonics with halide perovskites.Item Nanoimprinted Perovskite Metasurface for Enhanced Photoluminescence(Optical Soc Amer, 2018-11-05) Wang, Honglei; Liu, Shih-Chia; Balachandran, Balasubramaniam; Moon, Jiyoung; Haroldson, Ross; Li, Zhitong; Ishteev, Artur; Gu, Qing; Zhou, Weidong; Zakhidov, Anvar A.; Hu, Wenchuang (Walter); 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Wang, Honglei; Balachandran, Balasubramaniam; Moon, Jiyoung; Haroldson, Ross; Li, Zhitong; Gu, Qing; Zakhidov, Anvar A.; Hu, Wenchuang (Walter)Recently, solution-processed hybrid halide perovskite has emerged as promising materials for advanced optoelectronic devices such as photovoltaics, photodetectors, light emitting diodes and lasers. In the mean time, all-dielectric metasurfaces with high-index materials have attracted attention due to their low-loss and high-efficient optical resonances. Because of its tunable by composition band gap in the visible frequencies, organolead halide perovskite could serve as a powerful platform for realizing high-index, low-loss metasurfaces. However, direct patterning of perovskite by lithography-based technique is not feasible due to material instability under moisture. Here we report novel organolead halide perovskite metasurfaces created by the cost-effective thermal nanoimprint technology. The nanoimprinted perovskite metasurface showed improved surface morphology and enhanced optical absorption properties. Significantly enhanced optical emission with an eight-fold enhancement in photoluminescence (PL) intensity was observed under room temperature. Temperature-dependent PL of perovskite nanograting metasurface was also investigated. Based on our results, we believe that thermal nanoimprint is a simple and cost-effective technique to fabricate perovskite-based metasurfaces, which could have broad impact on optoelectronic and photonic applications.Item Tunable Organic PV Parallel Tandem with Ionic Gating(Amer Inst Physics, 2018-10-22) Saranin, Danila; Ishteev, Artur; Cook, Alexander B.; Yuen, Jonathan D.; Kuznetsov, Denis; Orlova, Marina; Didenko, Sergey; Zakhidov, Anvar; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Cook, Alexander B.; Yuen, Jonathan D.; Zakhidov, AnvarA novel type of tunable organic photovoltaic (OPV) tandem device with ionic gating by in-situ ionic liquid is presented. This device is comprised of two solution-processed polymeric OPV cells connected in parallel by a dry-laminated transparent multiwall carbon nanotube (MWCNT) interlayer. The interlayer MWCNT of this 3-terminal tandem device plays a role of a common electrode with a Fermi level that can be tuned via ionic gating to turn it into a common cathode, collecting photo-generated electrons from both sub-cells. Ionic gating employs electric double layer charging of the MWCNT in order to lower the work function of the common CNT electrode and increase its n-type conductivity. This tandem device is fabricated in ambient conditions via dry-lamination of MWCNT transparent sheets The new results demonstrating the different regimes of ionic gating at low, medium, and high gating voltages V_{gate} are presented, showing the optimal doping of the MWCNT, then favorable doping of acceptor PCBM ([6,6]-phenyl-C₆₁-butyric acid methyl ester), followed by the deterioration of performance at V_{gate} over the threshold voltage when doping of polymeric layers of sub-cell OPVs starts taking place. The doping of PCBM and polymers is additionally confirmed by the change in the charging and discharging current dynamics at high V_{gate} above the threshold.Item Upper Critical Field and Kondo Effects in Fe(Te{0.9} Se{0.1}) Thin Films by Pulsed Field Measurements(Nature Publishing Group, 2016-02-10) Salamon, Myron B.; Cornell, N.; Jaime, M.; Balakirev, F. F.; Zakhidov, Anvar A.; Huang, J.; Wang, H.; 0000 0001 0965 7058 (Salamon, MB); 0000-0003-3983-2229 (Zakhidov, AA); Salamon, Myron B.; Zakhidov, Anvar A.The transition temperatures of epitaxial films of Fe(Te{0.9} Se {0.1}) are remarkably insensitive to applied magnetic field, leading to predictions of upper critical fields B{c2}(T = 0) in excess of 100 T. Using pulsed magnetic fields, we find B{c2}(0) to be on the order of 45 T, similar to values in bulk material and still in excess of the paramagnetic limit. The same films show strong magnetoresistance in fields above B{c2}(T), consistent with the observed Kondo minimum seen above T{c}. Fits to the temperature dependence in the context of the WHH model, using the experimental value of the Maki parameter, require an effective spin-orbit relaxation parameter of order unity. We suggest that Kondo localization plays a similar role to spin-orbit pair breaking in making WHH fits to the data.Item Tunable Color Parallel Tandem Organic Light Emitting Devices with Carbon Nanotube and Metallic Sheet Interlayers(American Institute of Physics, 2015-11-19) Oliva, Jorge; Papadimitratos, Alexios; Desirena, Haggeo; De la Rosa, Elder; Zakhidov, Anvar A.; Zakhidov, Anvar A.Parallel tandem organic light emitting devices (OLEDs) were fabricated with transparent multiwall carbon nanotube sheets (MWCNT) and thin metal films (Al, Ag) as interlayers. In parallel monolithic tandem architecture, the MWCNT (or metallic films) interlayers are an active electrode which injects similar charges into subunits. In the case of parallel tandems with common anode (C. A.) of this study, holes are injected into top and bottom subunits from the common interlayer electrode; whereas in the configuration of common cathode (C. C.), electrons are injected into the top and bottom subunits. Both subunits of the tandem can thus be monolithically connected functionally in an active structure in which each subunit can be electrically addressed separately. Our tandem OLEDs have a polymer as emitter in the bottom subunit and a small molecule emitter in the top subunit. We also compared the performance of the parallel tandem with that of in series and the additional advantages of the parallel architecture over the in-series were: tunable chromaticity, lower voltage operation, and higher brightness. Finally, we demonstrate that processing of the MWCNT sheets as a common anode in parallel tandems is an easy and low cost process, since their integration as electrodes in OLEDs is achieved by simple dry lamination process.Item Microwave Conductance of Aligned Multiwall Carbon Nanotube Textile Sheets(2014-12-30) Brown, Brian L.; Bykova, Julia S.; Howard, Austin R.; Zakhidov, Anvar A.; Shaner, Eric A.; Lee, Mark; Brown, Brian L.; Bykova, Julia S.; Howard, Austin R.; Zakhidov, Anvar A.; Lee, MarkMultiwall carbon nanotube (MWNT) sheets are a class of nanomaterial-based multifunctional textile with potentially useful microwave properties. To understand better the microwave electrodynamics, complex AC conductance measurements from 0.01 to 50 GHz were made on sheets of highly aligned MWNTs with the alignment texture both parallel and perpendicular to the microwave electric field polarization. In both orientations, the AC conductance is modeled to first order by a parallel frequency-independent conductance and capacitance with no inductive contribution. This is consistent with low-frequency diffusive Drude AC conduction up to 50 GHz, in contrast to the "universal disorder" AC conduction reported in many types of single-wall nanotube materials.Item Stable Doping of Carbon Nanotubes via Molecular Self Assembly(2014-10-13) Lee, B.; Chen, Y.; Cook, Alex; Zakhidov, Anvar A.; Podzorov, V.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl tri-chloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60-300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (~100 cm² V⁻¹ s⁻¹). The hole density induced by the FTS monolayer in CNT sheets is estimated to be similar to 1.8 x 10¹⁴ cm⁻². We also show that FTS doping of CNT anodes greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in large area samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics.Item Superconductivity in an inhomogeneous bundle of metallic and semiconducting nanotubes(2013-09-06) Grigorenko, I.; Zakhidov, Anvar A.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.Using Bogoliubov-de Gennes formalism for inhomogeneous systems, we have studied superconducting properties of a bundle of packed carbon nanotubes, making a triangular lattice in the bundle's transverse cross-section. The bundle consists of a mixture of metallic and doped semiconducting nanotubes, which have different critical transition temperatures. We investigate how a spatially averaged superconducting order parameter and the critical transition temperature depend on the fraction of the doped semiconducting carbon nanotubes in the bundle. Our simulations suggest that the superconductivity in the bundle will be suppressed when the fraction of the doped semiconducting carbon nanotubes will be less than 0.5, which is the percolation threshold for a two-dimensional triangular lattice.Item Electrochemically Gated Organic Photovoltaic with Tunable Carbon Nanotube Cathodes(2013-10-18) Cook, Alexander B.; Yuen, Jonathan D.; Zakhidov, Anvar A.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We demonstrate an organic photovoltaic (OPV) device with an electrochemically gated carbon nanotube (CNT) charge collector. Bias voltages applied to the gate electrode reconfigure the common CNT electrode from an anode into a cathode which effectively collects photogenerated electrons, dramatically increasing all solar cell parameters to achieve a power conversion efficiency of ∼3%. This device requires very little current to initially charge and the leakage current is negligible compared to the photocurrent. This device can also be viewed as a hybrid tandem OPV-supercapacitor with a common CNT electrode. Other regimes of operation are briefly discussed.Item Lambertian White Top-Emitting Organic Light Emitting Device with Carbon Nanotube Cathode(2012-12-04) Freitag, P.; Zakhidov, Al A.; Luessem, B.; Zakhidov, Anvar A.; Leo, K.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We demonstrate that white organic light emitting devices (OLEDs) with top carbon nanotube (CNT) electrodes show almost no microcavity effect and exhibit essentially Lambertian emission. CNT top electrodes were applied by direct lamination of multiwall CNT sheets onto white small molecule OLED stack. The devices show an external quantum efficiency of 1.5% and high color rendering index of 70. Due to elimination of the cavity effect, the devices show good color stability for different viewing angles. Thus, CNT electrodes are a viable alternative to thin semitransparent metallic films, where the strong cavity effect causes spectral shift and non-Lambertian angular dependence. Our method of the device fabrication is simple yet effective and compatible with virtually any small molecule organic semiconductor stack. It is also compatible with flexible substrates and roll-to-roll fabrication.Item Effects of Nanostructure Geometry on Nanoimprinted Polymer Photovoltaics(RSC Pub, 2014-04-23) Yang, Yi; Mielczarek, Kamil; Aryal, Mukti; Zakhidov, Anvar A.; Hu, Wenchuang (Walter); 0000 0003 5287 0481 (Zakhidov, AA); 2005061514 (Hu, W); Zakhidov, Anvar A.; Hu, Wenchuang (Walter)We demonstrate the effects of nanostructure geometry on the nanoimprint induced poly(3-hexylthiophene-2,5-diyl) (P3HT) chain alignment and the performance of nanoimprinted photovoltaic devices. Out-of-plane and in-plane grazing incident X-ray diffraction techniques are employed to characterize the nanoimprint induced chain alignment in P3HT nanogratings with different widths, spacings and heights. We observe the dependence of the crystallite orientation on nanostructure geometry such that a larger width of P3HT nanogratings leads to more edge-on chain alignment while the increase in height gives more vertical alignment. Consequently, P3HT/6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) solar cells with the highest density and aspect ratio P3HT nanostructures show the highest power conversion efficiency among others, which is attributed to the efficient charge separation, transport and light absorption.