Showing papers by "Yang Yang published in 2013"

A polymer tandem solar cell with 10.6% power conversion efficiency

Abstract: An effective way to improve polymer solar cell efficiency is to use a tandem structure, as a broader part of the spectrum of solar radiation is used and the thermalization loss of photon energy is minimized. In the past, the lack of high-performance low-bandgap polymers was the major limiting factor for achieving high-performance tandem solar cell. Here we report the development of a high-performance low bandgap polymer (bandgap 60% and spectral response that extends to 900 nm, with a power conversion efficiency of 7.9%. The polymer enables a solution processed tandem solar cell with certified 10.6% power conversion efficiency under standard reporting conditions (25 °C, 1,000 Wm(-2), IEC 60904-3 global), which is the first certified polymer solar cell efficiency over 10%.

25th Anniversary Article: A Decade of Organic/Polymeric Photovoltaic Research

Abstract: Organic photovoltaic (OPV) technology has been developed and improved from a fancy concept with less than 1% power conversion efficiency (PCE) to over 10% PCE, particularly through the efforts in the last decade. The significant progress is the result of multidisciplinary research ranging from chemistry, material science, physics, and engineering. These efforts include the design and synthesis of novel compounds, understanding and controlling the film morphology, elucidating the device mechanisms, developing new device architectures, and improving large-scale manufacture. All of these achievements catalyzed the rapid growth of the OPV technology. This review article takes a retrospective look at the research and development of OPV, and focuses on recent advances of solution-processed materials and devices during the last decade, particular the polymer version of the materials and devices. The work in this field is exciting and OPV technology is a promising candidate for future thin film solar cells.

Solution-processed small-molecule solar cells: breaking the 10% power conversion efficiency

Abstract: A two-dimensional conjugated small molecule (SMPV1) was designed and synthesized for high performance solution-processed organic solar cells. This study explores the photovoltaic properties of this molecule as a donor, with a fullerene derivative as an acceptor, using solution processing in single junction and double junction tandem solar cells. The single junction solar cells based on SMPV1 exhibited a certified power conversion efficiency of 8.02% under AM 1.5 G irradiation (100 mW cm−2). A homo-tandem solar cell based on SMPV1 was constructed with a novel interlayer (or tunnel junction) consisting of bilayer conjugated polyelectrolyte, demonstrating an unprecedented PCE of 10.1%. These results strongly suggest solution-processed small molecular materials are excellent candidates for organic solar cells.

10.2% Power Conversion Efficiency Polymer Tandem Solar Cells Consisting of Two Identical Sub-Cells

Abstract: Polymer tandem solar cells with 102% power conversion efficiency are demonstrated via stacking two PDTP-DFBT:PC₇₁ BM bulk heterojunctions, connected by MoO₃/PEDOT:PSS/ZnO as an interconnecting layer The tandem solar cells increase the power conversion efficiency of the PDTP-DFBT:PC₇₁ BM system from 81% to 102%, successfully demonstrating polymer tandem solar cells with identical sub-cells of double-digit efficiency

A Selenium‐Substituted Low‐Bandgap Polymer with Versatile Photovoltaic Applications

Abstract: IO N Organic photovoltaic (OPV) devices provide an opportunity to utilize the solar energy effi ciently while maintaining low cost. [ 1 ] To harvest a greater part of the solar spectrum, lowering the energy bandgap of the active material is a major task for materials scientists. The design and synthesis of low-bandgap (LBG) conjugated polymers for use as electron donor materials for bulk heterojuction (BHJ) polymer solar cell (PSC) applications have attracted remarkable attention during the last decade. [ 2 ] The reasons for pursuing LBG polymers include: 1) The Shockley-Quiesser equation indicates a bandgap of around 1.4 eV is ideal for a single junction solar cell device. [ 3 ]

CZTS nanocrystals: a promising approach for next generation thin film photovoltaics

Abstract: Cu2ZnSn(S,Se)4 (CZTSSe) has received considerable attention as a material capable of driving the development of low-cost and high performance photovoltaics. Its high absorption coefficient, optimal band gap, and non-toxic, naturally abundant elemental constituents give it a number of advantages over most thin film absorber materials. In this manuscript, we discuss the current status of CZTSSe photovoltaics, and provide a comprehensive review of Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) nanocrystal (NCs)-based fabrication methods and solar cell characteristics. The focus will be on the relevant synthetic chemistry, film deposition, and the production of high efficiency photovoltaic devices. Various colloidal synthesis routes are currently used to form the highest quality CZTSSe film from the nanocrystals with controllable phase, size, shape, composition, and surface ligands. A variety of recipes are summarized for producing nanocrystal inks that are appropriate for forming CZTSSe absorber materials with a wide range of controllable optoelectronic properties. Deposition and post-processing, such as annealing and selenization treatments, play an important role in defining the phase and structure of the resulting material. Various film treatment strategies are outlined here, and their resulting material quality, device performance, and dominant photovoltaic loss mechanisms are discussed. Suggestions regarding needed improvements and future research directions are provided based on the current field of available literature.

Surface Charge and Cellular Processing of Covalently Functionalized Multiwall Carbon Nanotubes Determine Pulmonary Toxicity

Abstract: Functionalized carbon nanotubes (f-CNTs) are being produced in increased volume because of the ease of dispersion and maintenance of the pristine material physicochemical properties when used in composite materials as well as for other commercial applications. However, the potential adverse effects of f-CNTs have not been quantitatively or systematically explored. In this study, we used a library of covalently functionalized multiwall carbon nanotubes (f-MWCNTs), established from the same starting material, to assess the impact of surface charge in a predictive toxicological model that relates the tubes’ pro-inflammatory and pro-fibrogenic effects at cellular level to the development of pulmonary fibrosis. Carboxylate (COOH), polyethylene glycol (PEG), amine (NH2), sidewall amine (sw-NH2), and polyetherimide (PEI)-modified MWCNTs were successfully established from raw or as-prepared (AP-) MWCNTs and comprehensively characterized by TEM, XPS, FTIR, and DLS to obtain information about morphology, length, de...

Synthesis of 5H-Dithieno[3,2-b:2′,3′-d]pyran as an Electron-Rich Building Block for Donor–Acceptor Type Low-Bandgap Polymers

Abstract: We describe the detailed synthesis and characterization of an electron-rich building block, dithienopyran (DTP), and its application as a donor unit in low-bandgap conjugated polymers. The electron-donating property of the DTP unit was found to be the strongest among the most frequently used donor units such as benzodithiophene (BDT) or cyclopentadithiophene (CPDT) units. When the DTP unit was polymerized with the strongly electron-deficient difluorobenzothiadiazole (DFBT) unit, a regiorandom polymer (PDTP–DFBT, bandgap = 1.38 eV) was obtained. For comparison with the DTP unit, polymers containing alternating benzodithiophene (BDT) or cyclopentadithiophene (CPDT) units and the DFBT unit were synthesized (PBDT–DFBT and PCPDT–DFBT). We found that the DTP based polymer PDTP–DFBT shows significantly improved solubility and processability compared to the BDT or CPDT based polymers. Consequently, very high molecular weight and soluble PDTP–DFBT can be obtained with less bulky side chains. Interestingly, PDTP–DF...

High-performance semi-transparent polymer solar cells possessing tandem structures

Abstract: In this study we employed tandem device architectures to tune the external appearance and light-conversion properties of polymer solar cells (PSCs) from visibly transparent to semi-transparent, making them more versatile for integrated photovoltaic applications and more efficient under solar illumination. Our best transparent solar cell was a tandem PSC exhibiting an efficiency of 6.4% and a maximum transmission of 51% at 550 nm; in contrast, a semi-transparent tandem PSC having an average transmission of 30% in the visible range exhibited an efficiency greater than 7%.

Heterogeneous Cellular Networks: Theory, Simulation and Deployment

Abstract: This detailed, up-to-date introduction to heterogeneous cellular networking introduces its characteristic features, the technology underpinning it and the issues surrounding its use. Comprehensive and in-depth coverage of core topics catalogue the most advanced, innovative technologies used in designing and deploying heterogeneous cellular networks, including system-level simulation and evaluation, self-organisation, range expansion, cooperative relaying, network MIMO, network coding and cognitive radio. Practical design considerations and engineering tradeoffs are also discussed in detail, including handover management, energy efficiency and interference management techniques. A range of real-world case studies, provided by industrial partners, illustrate the latest trends in heterogeneous cellular networks development. Written by leading figures from industry and academia, this is an invaluable resource for all researchers and practitioners working in the field of mobile communications.

Rational defect passivation of Cu2ZnSn(S,Se)4 photovoltaics with solution-processed Cu2ZnSnS4:Na nanocrystals.

Abstract: An effective defect passivation route has been demonstrated in the rapidly growing Cu2ZnSn(S,Se)4 (CZTSSe) solar cell device system by using Cu2ZnSnS4:Na (CZTS:Na) nanocrystals precursors. CZTS:Na nanocrystals are obtained by sequentially preparing CZTS nanocrystals and surface decorating of Na species, while retaining the kesterite CZTS phase. The exclusive surface presence of amorphous Na species is proved by X-ray photoluminescence spectrum and transmission electron microscopy. With Na-free glasses as the substrate, CZTS:Na nanocrystal-based solar cell device shows 50% enhancement of device performance (∼6%) than that of unpassivated CZTS nanocrystal-based device (∼4%). The enhanced electrical performance is closely related to the increased carrier concentration and elongated minority carrier lifetime, induced by defect passivation. Solution incorporation of extrinsic additives into the nanocrystals and the corresponding film enables a facile, quantitative, and versatile approach to tune the defect pro...

Active layer-incorporated, spectrally tuned Au/SiO2 core/shell nanorod-based light trapping for organic photovoltaics.

Abstract: We demonstrate that incorporation of octadecyltrimethoxysilane (OTMS)-functionalized, spectrally tuned, gold/silica (Au/SiO2) core/shell nanospheres and nanorods into the active layer of an organic photovoltaic (OPV) device led to an increase in photoconversion efficiency (PCE). A silica shell layer was added onto Au core nanospheres and nanorods in order to provide an electrically insulating surface that does not interfere with carrier generation and transport inside the active layer. Functionalization of the Au/SiO2 core/shell nanoparticles with the OTMS organic ligand was then necessary to transfer the Au/SiO2 core/shell nanoparticles from an ethanol solution into an OPV polymer-compatible solvent, such as dichlorobenzene. The OTMS-functionalized Au/SiO2 core/shell nanorods and nanospheres were then incorporated into the active layers of two OPV polymer systems: a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCB60M) OPV device and a poly[2,6-4,8-di(5-ethylhexylthienyl)benzo[1...

Elliptic flow of identified hadrons in Au+Au collisions at s NN =7.7-62.4 GeV

Abstract: Measurements of the elliptic flow, upsilon(2), of identified hadrons (pi(+/-), K-+/-, K-s(0), p, (p) over bar, phi, Lambda, (Lambda) over bar, Xi(-), (Xi) over bar (+), Omega(-), (Omega) over bar (+)) in Au + Au collisions at root s(NN) = 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV are presented. The measurements were done at midrapidity using the time-projection chamber and the time-of-flight detectors of the Solenoidal Tracker at RHIC experiment during the beam-energy scan program at Relativistic Heavy Ion Collider. A significant difference in the upsilon(2) values for particles and the corresponding antiparticles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, root s(NN) (or increasing baryon chemical potential, mu(B)), and is larger for the baryons as compared to the mesons. This implies that particles and antiparticles are no longer consistent with the universal number-of-constituent quark (NCQ) scaling of upsilon(2) that was observed at root s(NN) = 200 GeV. However, for the selected group of particles (p(+), K+, K-s(0), p, Lambda, Xi(-), Omega(-)) NCQ scaling at (m(T) - m(0))/n(q) > 0.4 GeV/c(2) is not violated within +/- 10%. The upsilon(2) values for f mesons at 7.7 and 11.5 GeV are approximately two standard deviations from the trend defined by the other hadrons at the highest measured p(T) values.

Interference Graph-Based Resource-Sharing Schemes for Vehicular Networks

Abstract: This paper investigates the resource-sharing problem in vehicular networks, including both vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication links. A novel underlaying resource-sharing communication mode for vehicular networks is proposed, in which different V2V and V2I communication links are permitted to access the same resources for their individual data transmission. To solve the resource-sharing problem in vehicular networks, we, for the first time, apply graph theory and propose the following two interference graph-based resource-sharing schemes: 1) the interference-aware graph-based resource-sharing scheme and 2) the interference-classified graph-based resource-sharing scheme. Compared with the traditional orthogonal communication mode in vehicular networks, the proposed two resource-sharing schemes express better network sum rate. The utility of the proposed V2V and V2I underlaying communication mode and the two proposed interference graph-based resource-sharing schemes are verified by simulations.

Synthesis of nonstoichiometric zinc ferrite nanoparticles with extraordinary room temperature magnetism and their diverse applications

Abstract: A series of nonstoichiometric zinc ferrite (ZndFe3−dO4) nanoparticles with Zn-dopant concentration d ranging from 0 to 0.5 was synthesized via thermal decomposition route employing oleic acid as surfactant. The zinc dopant concentration was controlled by the ratio of Zn/Fe precursors. High room temperature saturation magnetization of 110 emu g−1 was obtained for large Zn ferrite particles (more than 100 nm) with nominal composition of Zn0.468Fe2.532O4. The origin of the extraordinary magnetic property was revealed as the Zn substitution of Fe atoms at the tetrahedral site (A site) in the spinel magnetite phase. It was found that the precursor/surfactant ratio was an important parameter for the control of the shape and size of as-synthesized Zn ferrite particles. The details were investigated through a series of experimental work. Size-dependent applications, such as radar absorption and magnetic fluid hyperthermia, were further studied. Both applications required magnetic particles with high saturation magnetization, hence our samples displayed advantages over Fe3O4 magnetite nanoparticles. Especially for magnetic fluid hyperthermia, 26 nm Zn ferrite nanoparticles coated by P-mPEG polymer showed superior biocompatibility and heating efficiency, implying the potential usefulness to in vivo cancer therapy.

Relating Recombination, Density of States, and Device Performance in an Efficient Polymer:Fullerene Organic Solar Cell Blend

Abstract: We explore the interrelation between density of states, recombination kinetics, and device performance in effi cient poly(4,8-bis-(2-ethylhexyloxy)- benzo(1,2-b:4,5-b')dithiophene-2,6-diyl-alt-4-(2-ethylhexyloxy-1-one) thieno(3,4-b)thiophene-2,6-diyl):(6,6)-phenyl-C 71 -butyric acid methyl ester (PBDTTT-C:PC 71 BM) bulk-heterojunction organic solar cells. We modulate the active-layer density of states by varying the polymer:fullerene com- position over a small range around the ratio that leads to the maximum solar cell effi ciency (50-67 wt% PC 71 BM). Using transient and steady-state techniques, we fithat nongeminate recombination limits the device effi - ciency and, moreover, that increasing the PC 71 BM content simultaneously increases the carrier lifetime and drift mobility in contrast to the behavior expected for Langevin recombination. Changes in electronic properties with fullerene content are accompanied by a signifi cant change in the magnitude or energetic separation of the density of localized states. Our comprehensive approach to understanding device performance represents signifi cant progress in understanding what limits these high-effi ciency polymer:fullerene systems.

Nanoscale Dispersions of Gelled SnO2: Material Properties and Device Applications

Abstract: High intrinsic carrier mobility and excellent transparency at visible wavelengths make stannic oxide (SnO2) a material of interest for a variety of optoelectronic applications. Here, we demonstrate a solvothermal route to stabilize gelled dispersions of tin oxide nanoparticles with diameters in the range of 2–4 nm. Small particle dimensions ultimately allow for the deposition of smooth thin films with all of the useful properties that can be expected from this material system. The structural and morphological properties of the deposited films are investigated, and they are demonstrated as an electron collection layer in polymer-based organic photovoltaic cells with promising power conversion efficiencies.

Solution-processed small molecules using different electron linkers for high-performance solar cells.

Abstract: Conjugated acceptor-donor-acceptor small molecules using different electron linkers are designed, synthesized, and used in organic solar cells. All of these small molecules show high photoconversion efficiencies (PCEs), ranging from 3.18-6.15% under simulated AM 1.5G condition. A maximum PCE of 6.15% combined with a high Voc of 0.85 V, a Jsc of 10.79 mA cm(-2) and a notable FF of 67.1% are achieved with T3/PC71 BM blend based devices using polydimethylsiloxane as additive.

Targeted Polysaccharide Nanoparticle for Adamplatin Prodrug Delivery

Abstract: A series of conjugated hyaluronic acid particles (HAP), composed of a hydrophobic anticancer drug core and hydrophilic cyclodextrin/hyaluronic acid shell, were prepared through self-assembling and characterized by 1H NMR titration, electron microscopy, zeta potential, and dynamic light-scattering experiments. The nanometer-sized HAP thus prepared was biocompatible and biodegradable and was well-recognized by the hyaluronic acid receptors overexpressed on the surface of cancer cells, which enabled us to exploit HAP as an efficient targeted delivery system for anticancer drugs. Indeed, HAP exhibited anticancer activities comparable to the commercial anticancer drug cisplatin but with lower side effects both in vitro and in vivo.

J-aggregation of a squaraine dye and its application in organic photovoltaic cells

Abstract: In this paper, we investigated the aggregation behavior of a squaraine dye in solid films, as well as the effects on its optical and electrical properties. We observed a strong intermolecular interaction in thin films, which can be controlled via processing solvents. Two typical aggregation behaviors, i.e. H- and J- aggregation, can be selectively formed via the proper selection of solvents, resulting in a significant difference in material properties and the resultant photovoltaic performance. In addition to the monomer absorption between 600 nm and 700 nm, the H-aggregation mainly absorbs green light around 500–600 nm, while the J-aggregation shows a strong absorption in the near infrared range up to 850 nm. Therefore in squaraine/fullerene bi-layer hetero-junction photovoltaic cells, we demonstrated a significant contribution of J-aggregation to the photocurrent. Furthermore the J-aggregation films have a deeper ionization potential, most likely due to the intermolecular charge-transfer interaction, and thus gave rise to a larger open circuit voltage than those of the H-aggregation based devices. The J-aggregation formation shall be considered as an effective approach to tune the optical/electrical properties in organic optoelectronic devices.

Observation of an energy-dependent difference in elliptic flow between particles and antiparticles in relativistic heavy ion collisions

Abstract: Elliptic flow (v(2)) values for identified particles at midrapidity in Au + Au collisions, measured by the STAR experiment in the beam energy scan at RHIC at root s(NN) = 7.7-62.4 GeV, are presented. A beamenergy-dependent difference of the values of v(2) between particles and corresponding antiparticles was observed. The difference increases with decreasing beam energy and is larger for baryons compared to mesons. This implies that, at lower energies, particles and antiparticles are not consistent with the universal number-of-constituent-quark scaling of v(2) that was observed at root s(NN) = 200 GeV. DOI: 10.1103/PhysRevLett.110.142301

Third harmonic flow of charged particles in Au + Au collisions at √sNN = 200 GeV

Abstract: In this proceedings, we report measurements of the third harmonic coefficient of the azimuthal anisotropy, v3, known as triangular flow. The analysis is for charged particles near midrapidity in Au+Au collisions at GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. Triangular flow as a function of centrality, pseudorapidity and transverse momentum are reported using various methods, including a study of the signal for particle pairs as a function of their pseudorapidity separation. Results are compared with other experiments and model predictions.