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    Organic halides and nanocone plastic structures enhance the energy conversion efficiency and self-cleaning ability of colloidal quantum dot photovoltaic devices

    , Article Journal of Physical Chemistry C ; Volume 121, Issue 18 , 2017 , Pages 9757-9765 ; 19327447 (ISSN) Tavakoli, M. M ; Simchi, A ; Tavakoli, R ; Fan, Z ; Sharif University of Technology
    American Chemical Society  2017
    Abstract
    This paper presents solid-state ligand exchange of spin-coated colloidal lead sulfide quantum dot (PbS QD) films by methylammonium iodide (MAI) and integration of them in depleted heterojunction solar (DHS) devices having an antireflecting (AR) nanocone plastic structure. Time-resolved photoluminescence measurements determine a shorter lifetime of the charge carries on a semiconductor (TiO2) electron transfer layer for the MAI-passivated QD films as compared with those with long-chain aliphatic or short thiol ligands. Consequently, the DHS device yields improved power conversion efficiency (>125%) relative to oleic-acid-passivated PbS QD films. Using anodized aluminum oxide templates, an... 

    Surface engineering of TiO2 ETL for highly efficient and hysteresis-less planar perovskite solar cell (21.4%) with enhanced open-circuit voltage and stability

    , Article Advanced Energy Materials ; Volume 8, Issue 23 , 2018 ; 16146832 (ISSN) Tavakoli, M. M ; Yadav, P ; Tavakoli, R ; Kong, J ; Sharif University of Technology
    Wiley-VCH Verlag  2018
    Abstract
    Interfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high-performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO2 (a-SnO2) between the TiO2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double-layer structure of TiO2 compact layer (c-TiO2) and a-SnO2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a-SnO2/c-TiO2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c-TiO2 based device.... 

    Efficient, hysteresis-free, and flexible inverted perovskite solar cells using all-vacuum processing.Efficient, hysteresis-free, and flexible inverted perovskite solar cells using all-vacuum processing

    , Article Solar RRL ; 2020 Tavakoli, M. M ; Yadav, P ; Prochowicz, D ; Tavakoli, R ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    The fabrication of efficient perovskite solar cells (PSCs) using all-vacuum processing is still challenging due to the limitations in the vacuum deposition of the hole transporting layer (HTL). Herein, inverted PSCs using copper (II) phthalocyanine (CuPC) as an ideal alternative HTL for vacuum processing are fabricated. After proper optimization, a PSC with a power conversion efficiency (PCE) of 20.3% is achieved, which is much better than the PCEs (16.8%) of devices with solution-based CuPC. As it takes a long time to dissolve CuPC in the solution-based device, the evaporation approach has better advantage in terms of fast processing. In addition, the device with the evaporated CuPC HTL... 

    Efficient perovskite solar cells based on Cdse/Zns quantum dots electron transporting layer with superior UV stability

    , Article Physica Status Solidi - Rapid Research Letters ; Volume 14, Issue 6 , 2020 Tavakoli, M. M ; Prochowicz, D ; Yadav, P ; Tavakoli, R ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    Stability is the main challenge in the field of perovskite solar cells (PSCs). Finding new strategies is required to protect the PSCs from deteriorating agents such as humidity, heating, and illumination. Herein, a new electron transporting layer (ETL), i.e., CdSe/ZnS quantum dots (QDs), is proposed for the fabrication of efficient and stable PSCs. CdSe/ZnS QDs layer not only works as an ETL but also has downshifting property, which can improve both efficiency and stability of the PSCs. Using CdSe/ZnS QDs ETL with green emission, a PSC with maximum power conversion efficiency (PCE) of 18% is achieved. More importantly, the device shows great UV stability, much better than the device with... 

    The effect of fuel cell operational conditions on the water content distribution in the polymer electrolyte membrane

    , Article Renewable Energy ; Volume 36, Issue 12 , December , 2011 , Pages 3319-3331 ; 09601481 (ISSN) Tavakoli, B ; Roshandel, R ; Sharif University of Technology
    2011
    Abstract
    Models play an important role in fuel cell design and development. One of the critical problems to overcome in the proton exchange membrane (PEM) fuel cells is the water management. In this work a steady state, two-dimensional, isothermal model in a single PEM fuel cell using individual computational fluid dynamics code was presented. Special attention was devoted to the water transport through the membrane which is assumed to be combined effect of diffusion, electro-osmotic drag and convection. The effect of current density variation distribution on the water content (λ) in membrane/electrode assembly (MEA) was determined. In this work the membrane heat conductivity is considered as a... 

    Multilayer evaporation of MAFAPbI3-xClx for the fabrication of efficient and large-scale device perovskite solar cells

    , Article Journal of Physics D: Applied Physics ; Volume 52, Issue 3 , 2019 ; 00223727 (ISSN) Tavakoli, M. M ; Yadav, P ; Prochowicz, D ; Tavakoli, R ; Saliba, M ; Sharif University of Technology
    Institute of Physics Publishing  2019
    Abstract
    FAPbI3 perovskites are excellent candidates for fabrication of perovskite solar cells (PSCs) with high efficiency and stability. However, these perovskites exhibit phase instability problem at room temperature. In this work, to address this challenge we use methylammonium chloride (MACl) as an additive and employed a layer-by-layer thermal evaporation technique to fabricate high-quality perovskite films on a large scale of 25 cm2. The optimized perovskite films show high crystallinity with large grains in the μm-range and reveals phase stability due to the presence of MACl after the annealing process. Finally, we achieved PSCs with 17.7% and 15.9% for active areas of 0.1 cm2 and 0.8 cm2,... 

    A Dopant-free hole transporting layer for efficient and stable planar perovskite solar cells

    , Article Physica Status Solidi - Rapid Research Letters ; Volume 14, Issue 7 , 2020 Tavakoli, M. M ; Si, H ; Yadav, P ; Prochowicz, D ; Tavakoli, R ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    Herein, a new dopant-free organic material, PV2000, as a stable hole transporting layer (HTL) for the fabrication of stable and efficient perovskite solar cells (PSCs) is introduced. For this purpose, planar PSCs using a triple-A cation perovskite composition are fabricated and the commonly used 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) HTL is replaced by dopant-free PV2000 polymer. The characterization results disclose that the PV2000 has a great thermal stability, good hole mobility, and suitable band alignment that matches well with the valence band of triple-A cation perovskite. After proper optimization of PV2000 film thickness, a planar PSC... 

    Modeling water content distribution in the polymer electrolyte membrane of pem fuel cell

    , Article ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology. Collocated with ASME 2011 5th International Conference on Energy Sustainability, FUELCELL 2011, 7 August 2011 through 10 August 2011, Washington, DC ; 2011 , Pages 851-858 ; 9780791854693 (ISBN) Tavakoli, B. A ; Roshandel, R ; Sharif University of Technology
    2011
    Abstract
    Models play an important role in fuel cell design and development. One of the critical problems to overcome in the proton exchange membrane (PEM) fuel cells is the water management. In this work a steady state, two dimensional, isothermal model in a single PEM fuel cell using individual computational fluid dynamics code was presented. Special attention was devoted to the water transport through the membrane which is assumed to be combined effect of diffusion, electro osmotic drag and convection. The effect of current density variation distribution on the Water content (λ) in membrane/electrode assembly (MEA) was determined. After that detailed distribution of oxygen concentration, water... 

    All-Vacuum-processing for fabrication of efficient, large-scale, and flexible inverted perovskite solar cells

    , Article Physica Status Solidi - Rapid Research Letters ; 2020 Tavakoli, M. M ; Tavakoli, R ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    Vacuum deposition of transporting layers, especially the hole-transporting layer (HTL), is still a big challenge for the fabrication of large-area perovskite solar cells (PSCs). In this work, efficient and large-area PSCs are fabricated by thermal evaporation of all the layers. Poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) is used as the HTL, and a compact layer of PTAA with low thickness (2–10 nm) is successfully deposited using thermal evaporation. The optical and ultraviolet photoelectron spectroscopy (UPS) measurements prove that the evaporated PTAA has a great match with the single A-cation methylammonium triiodide perovskite film in terms of quenching effect and band... 

    Oxygen plasma-induced p-type doping improves performance and stability of PbS quantum dot solar cells

    , Article ACS Applied Materials and Interfaces ; Volume 11, Issue 29 , 2019 , Pages 26047-26052 ; 19448244 (ISSN) Tavakoli Dastjerdi, H ; Tavakoli, R ; Yadav, P ; Prochowicz, D ; Saliba, M ; Tavakoli, M. M ; Sharif University of Technology
    American Chemical Society  2019
    Abstract
    PbS quantum dots (QDs) have been extensively studied for photovoltaic applications, thanks to their facile and low-cost fabrication processing and interesting physical properties such as size dependent and tunable band gap. However, the performance of PbS QD-based solar cells is highly sensitive to the humidity level in the ambient air, which is a serious obstacle toward its practical applications. Although it has been previously revealed that oxygen doping of the hole transporting layer can mitigate the cause of this issue, the suggested methods to recover the device performance are time-consuming and relatively costly. Here, we report a low-power oxygen plasma treatment as a rapid and... 

    Efficient and less-toxic indium-doped mapbi3 perovskite solar cells prepared by metal alloying technique

    , Article Solar RRL ; Volume 6, Issue 9 , 2022 ; 2367198X (ISSN) Tavakoli, M. M ; Fazel, Z ; Tavakoli, R ; Akin, S ; Satapathi, S ; Prochowicz, D ; Yadav, P ; Sharif University of Technology
    John Wiley and Sons Inc  2022
    Abstract
    Perovskite materials with ABX3 structure (A: organic, B: metal, and X: halides) have attracted tremendous attention due to their outstanding optoelectronic properties. Herein, a novel approach is developed using chemical vapor deposition (CVD), i.e., metal alloying of halide-perovskite domain via ion-transfer (MAHDI) for the growth of high-quality perovskite films, grown directly from a metal precursor. This technique easily enables us to replace the toxic Pb metal (B site) with other metals using alloying approach. Using the proposed approach, we fabricated stable and efficient Pb–In perovskite solar cells (PSCs) with a maximum power conversion efficiency (PCE) of 21.2%, which is more... 

    A hybrid pole climbing and manipulating robot with minimum DOFs for construction and service applications

    , Article Industrial Robot ; Volume 32, Issue 2 , 2005 , Pages 171-178 ; 0143991X (ISSN) Tavakoli, M ; Zakerzadeh, M. R ; Vossoughi, G. R ; Bagheri, S ; Sharif University of Technology
    2005
    Abstract
    Purpose - Aims to describe design, prototyping and characteristics of a pole climbing/manipulating robot with ability of passing bends and branches of the pole. Design/methodology/approach - Introducing a hybrid (parallel/serial) four degree of freedom (DOF) mechanism as the main part of the robot and also introduces a unique gripper design for pole climbing robots. Findings - Finds that a robot, with the ability of climbing and manipulating on poles with bends and branches, needs at least 4 DOFs. Also an electrical cylinder is a good option for climbing robots and has some advantages over pneumatic or hydraulic cylinders. Research limitations/implications - The robot is semi-industrial... 

    On the glass-forming ability of (Zr0.5Cu0.5)100−xAlx ternary alloys: A molecular dynamics study

    , Article Materials Today Communications ; Volume 31 , 2022 ; 23524928 (ISSN) Abbasi, M. H ; Shabestari, S. G ; Tavakoli, R ; Sharif University of Technology
    Elsevier Ltd  2022
    Abstract
    In this research, the atomic scale local structures in (Zr0.5Cu0.5)100−xAlx (x = 0,2,4,6,8,10,12) bulk metallic glass was studied using molecular dynamics simulation method. The pair distribution function, Voronoi analysis and mean squared displacement (MSD) were adopted for investigation of the local structures. It was found that Cu- and Al-centered full icosahedra possess the most frequency accompanied by the most changes during the glass transition process in the supercooled liquid region temperature. Moreover, it was observed that the Al-centered full icosahedra (Al-FI) and Cu-centered full icosahedra (Cu-FI) clusters with 2.5% and 1.9% increase (relative to total atoms), respectively,... 

    Numerical simulation of liquid/gas phase flow during mold filling

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 196, Issue 1-3 , 2006 , Pages 697-713 ; 00457825 (ISSN) Tavakoli, R ; Babaei, R ; Varahram, N ; Davami, P ; Sharif University of Technology
    2006
    Abstract
    A numerical model for simulation of liquid/gas phase flow during mold filling is presented. The incompressible Navier-Stokes equations are discretized on a fixed Cartesian mesh with finite difference method. The fractional-step scheme is employed for enforcing incompressibility constraint. The free surface effects are calculated using the volume of fluid method based on the piecewise-linear interface reconstruction and split Lagrangian advection of volume fraction field. Adding limited compressibility to the gas phase led to improvement in convergence rate of Poisson equation solver (about 2-fold). This new concept permits simulation of two-phase incompressible free surface flow during mold... 

    A non-catalytic vapor growth regime for organohalide perovskite nanowires using anodic aluminum oxide templates

    , Article Nanoscale ; Volume 9, Issue 18 , 2017 , Pages 5828-5834 ; 20403364 (ISSN) Tavakoli, M. M ; Waleed, A ; Gu, L ; Zhang, D ; Tavakoli, R ; Lei, B ; Su, W ; Fang, F ; Fan, Z ; Sharif University of Technology
    Royal Society of Chemistry  2017
    Abstract
    In this work, a novel and facile synthesis process to fabricate single crystalline organometal halide perovskite nanowires has been successfully developed. Nanowires were grown in a high density ordered array from metal nanoclusters inside anodic aluminum oxide templates using a non-catalytic chemical vapor deposition method. Specifically, perovskite NWs were grown as a result of the reaction between methylammonium iodide (MAI) and the Pb/Sn (Pb or Sn) metal in anodic aluminum oxide templates under optimal conditions. The characterization results show that there is a reaction zone at the interface between the perovskite material and metal, at the bottom of the anodic aluminum oxide... 

    Comparison between different DPC methods applied to DFIG wind turbines

    , Article International Journal of Renewable Energy Research ; Volume 3, Issue 2 , 2013 , Pages 446-452 ; 13090127 (ISSN) Tavakoli, S. M ; Pourmina, M. A ; Zolghadri, M. R ; Sharif University of Technology
    2013
    Abstract
    In this paper the direct power control methods of doubly fed induction generator in wind turbine applications are studied. In the methods under study, the proper voltage space vector of the rotor side converter is selected using a switching table which is derived from flux position and the difference between the measured and reference stator active and reactive powers. Various simulations are performed in Matlab/Simulink software on a DFIG system in order to investigate the dynamic performance and robustness of the proposed control methods against machine internal parameters variations  

    Modeling hydrogen fluoride adsorption by sodium fluoride

    , Article Journal of Industrial and Engineering Chemistry ; Volume 16, Issue 6 , November , 2010 , Pages 978-985 ; 1226086X (ISSN) Afzal, S ; Rahimi, A ; Ehsani, M. R ; Tavakoli, H ; Sharif University of Technology
    2010
    Abstract
    In the current study, hydrogen fluoride (HF) adsorption onto the sodium fluoride pellets is modeled. For this purpose a two-dimensional, non-isothermal model was developed and the governing equations were solved numerically. The contributions of diffusion transport in axial and radial directions also were considered in mathematical formulations. The model results of effluent concentration and breakthrough curves of HF were compared with the experimental data obtained in a lab-scale adsorption unit, reported in our previous work [1]. The results indicate while the feed gas velocity decreases, the HF adsorption capacity on NaF is significantly enhanced and there is a delay in breakthrough... 

    Experimental study of hydrogen fluoride adsorption on sodium fluoride

    , Article Journal of Industrial and Engineering Chemistry ; Volume 16, Issue 1 , 2010 , Pages 147-151 ; 1226086X (ISSN) Afzal, S ; Rahimi, A ; Ehsani, M. R ; Tavakoli, H ; Sharif University of Technology
    2010
    Abstract
    In uranium conversion industry, the fluorine is used as chemical raw material gas to produce UF4 and UF6 while its purity is very important. In this study, the adsorption process of hydrogen fluoride, as an impurity in the process of fluorine production, on sodium fluoride pellets is experimentally studied in a lab-scale fixed bed adsorbent. Also, the effects of some operating parameters including inlet concentration and inlet temperature of hydrogen fluoride are precisely investigated on the adsorption process. The data of adsorption are analyzed and correlated by Langmuir, Freundlich and Temkin isotherms. The adsorption capacity is found to be 1.908 and 0.750 g HF/g NaF by the Langmuir... 

    Continuous-time user modeling in presence of badges: a probabilistic approach

    , Article ACM Transactions on Knowledge Discovery from Data ; Volume 12, Issue 3 , 2018 ; 15564681 (ISSN) Khodadadi, A ; Hosseini, A ; Tavakoli, E ; Rabiee, H. R ; Sharif University of Technology
    Association for Computing Machinery  2018
    Abstract
    User modeling plays an important role in delivering customized web services to the users and improving their engagement. However, most user models in the literature do not explicitly consider the temporal behavior of users. More recently, continuous-time user modeling has gained considerable attention and many user behavior models have been proposed based on temporal point processes. However, typical point process-based models often considered the impact of peer influence and content on the user participation and neglected other factors. Gamification elements are among those factors that are neglected, while they have a strong impact on user participation in online services. In this article,... 

    Effect of solid fraction, grain misorientation and grain boundary energy on solidification cracking in weld of Al-Cu aluminum alloys

    , Article Materials Research Express ; Volume 6, Issue 8 , 2019 ; 20531591 (ISSN) Bodaghi, F ; Movahedi, M ; Kokabi, A. H ; Tavakoli, R ; Sharif University of Technology
    Institute of Physics Publishing  2019
    Abstract
    Solidification cracking is one the most common types of cracking in the weld of the aluminum alloys. Although some numerical models have been developed for investigation of the solidification cracking, the effect of the grain misorientation on the solidification cracking susceptibility (SCS) of a weld has rarely been considered. This work studies the effect of the angle between the primary arms of the dendrites on the SCS. Hence, a solidification cracking model was developed given the grain misorientation in the convergence condition. The model was investigated for Al-Cu alloys. When the grain boundary energy was considered in the model, there was an increase in the SCS for misorientation...