Pyrite Nanocrystals Research Articles

Anisotropic Growth of Iron Pyrite FeS2 Nanocrystals via Oriented Attachment

Pyrite (FeS2) material is attractive for applications in solar cells, lithium batteries, and hydrogen production because of its abundant, nontoxic features as well as the extraordinary electrical and optical properties. Pyrite (FeS2) nanocrystals (NCs) were synthesized via hot injection method, and the crystalline structure and morphologic evolution of pyrite NCs were investigated. We found that pyrite (FeS2) NCs were generated from a mackinawite FeS0.94 nanosheets template. The initial anisotropic growth of NCs was dominated by oriented attachment mechanism. Ostwald ripening growth became obvious as time progressed, resulting in faceted NCs. In accordance with the analysis of high-resolution transmission electron microscopy (HRTEM) images and surface free energies, we found that the attachment occurs between the opposite facets with high surface free energies including (210)-Fe and (210)-2S as well as (001)-Fe and (001)-2S. The attachment could also happen through a “point-contact” followed by interparti...

Iron pyrite nanocrystal film serves as a copper-free back contact for polycrystalline CdTe thin film solar cells

We report the application of thin film nanocrystalline (NC) FeS2 as the copper-free back contact for CdTe solar cells. The FeS2-NC layer is prepared from solution directly on the CdTe surface using drop-casting coupled with a hydrazine treatment at ambient temperature and pressure, and requires no thermal treatment. Copper-free solar cells based on the CdS/CdTe/FeS2-NC/Au architecture exhibit device efficiencies >90% that of a standard Cu/Au back contact devices. The FeS2-NC back contact solar cells show good thermal stability under initial tests. Devices prepared with untreated FeS2-NC back contacts display a strong “S-kink” behavior which we correlate with a high hole-transport barrier arising from inter-NC organic surfactant molecules.

Structural, morphological, and optoelectronic properties of rod-like iron pyrite nanocrystals for solar cell applications

Semiconducting, octadecylamine (ODA)-capped, rod-like FeS2 nanocrystals (NCs) are prepared and their properties are characterized. Transmission electron microscopy studies revealed the lattice fringes were clearly visible, confirming that the rod-like FeS2 NCs obtained in this study were highly crystalline. X-ray diffraction (XRD) studies indicated that the structure of FeS2 NCs is in cubic phase. Optical properties showed that the FeS2 NCs can be a promising candidate for the electron acceptor material in the bulk hetero-junction (BHJ) solar cell applications. The power conversion efficiency of the BHJ solar cells using polymer and the rod-like FeS2 NCs with a structure of glass/ITO/PEDOT:PSS/(FeS2+polymer)/Al was found to be ∼0.45%.

Analysis and characterization of iron pyrite nanocrystals and nanocrystalline thin films derived from bromide anion synthesis

We use a solution-based bromide anion hot injection method to synthesize stable, phase pure and highly crystalline cubic iron pyrite (FeS2) nanocrystals, with size varying from ∼70 to ∼150 nm.

Pyrite (FeS2) nanocrystals as inexpensive high-performance lithium-ion cathode and sodium-ion anode materials.

In light of the impeding depletion of fossil fuels and necessity to lower carbon dioxide emissions, economically viable high-performance batteries are urgently needed for numerous applications ranging from electric cars to stationary large-scale electricity storage. Due to its low raw material cost, non-toxicity and potentially high charge-storage capacity pyrite (FeS2) is a highly promising material for such next-generation batteries. In this work we present the electrochemical performance of FeS2 nanocrystals (NCs) as lithium-ion and sodium-ion storage materials. First, we show that nanoscopic FeS2 is a promising lithium-ion cathode material, delivering a capacity of 715 mA h g(-1) and average energy density of 1237 Wh kg(-1) for 100 cycles, twice higher than for commonly used LiCoO2 cathodes. Then we demonstrate, for the first time, that FeS2 NCs can serve as highly reversible sodium-ion anode material with long cycling life. As sodium-ion anode material, FeS2 NCs provide capacities above 500 mA h g(-1) for 400 cycles at a current rate of 1000 mA g(-1). In all our tests and control experiments, the performance of chemically synthesized nanoscale FeS2 clearly surpasses bulk FeS2 as well as large number of other nanostructured metal sulfides.

Protein footprinting by pyrite shrink-wrap laminate

The structure of macromolecules and their complexes dictate their biological function. In "footprinting", the solvent accessibility of the residues that constitute proteins, DNA and RNA can be determined from their reactivity to an exogenous reagent such as the hydroxyl radical (·OH). While ·OH generation for protein footprinting is achieved by radiolysis, photolysis and electrochemistry, we present a simpler solution. A thin film of pyrite (cubic FeS2) nanocrystals deposited onto a shape memory polymer (commodity shrink-wrap film) generates sufficient ·OH via Fenton chemistry for oxidative footprinting analysis of proteins. We demonstrate that varying either time or H2O2 concentration yields the required ·OH dose-oxidation response relationship. A simple and scalable sample handling protocol is enabled by thermoforming the "pyrite shrink-wrap laminate" into a standard microtiter plate format. The low cost and malleability of the laminate facilitates its integration into high throughput screening and microfluidic devices.

FeS2 ultrathin films prepared using well-dispersed pyrite nanocrystal inks

Well-dispersed FeS2 pyrite nanocrystal inks were produced by bead milling. They were used to produce ultrathin films of ∼55 nm thickness. After annealing at 500 °C, the film thickness decreased, the crystallinity of the films increased, and a small amount of marcasite phase appeared. Optical measurements showed that the absorption coefficient of the annealed films increased as wavelength decreased and finally reached ∼2.2 × 105 cm−1. The annealed films retained p-type semiconductors and a band gap of 0.92 eV. The resistivity and mobility of the pyrite films before and after annealing were 100 Ω cm and 6 cm2 V−1 s−1, and 0.8 Ω cm, 30 cm2 V−1 s−1, respectively.

Growth Pattern and Its Indication of Spheroidal Nano-Micro Crystal Aggregates of Pyrite in the Baiyunpu Pb-Zn Polymetallic Deposit, Central Hunan

The Baiyunpu deposit lies in the southwest plunging Dachengshan anticline in central Hunan, which is a large Pb-Zn polymetallic deposit. The orebodies were surrounded by the Qiziqiao Formation limestone in the Middle Devonian, and its geological occurrence is consistent with the wall rocks. A large number of spheroidal pyrite aggregates are found unevenly distributed in the ores. The spheroidal aggregates are made up of kernels and concentric rings. The kernels are composed of approximately epigranular pyrite nanocrystals, while the rings are composed of accumulated pyrite microcrystals growing along the radial direction. The spheroidal pyrite aggregate and its outer zones can be divided into five areas (A–E). The results of electron probe micro analysis (EPMA) show that from the zone A1 to B, Co/Ni <1, the sum of Co and Ni is 0.08%−0.26%, S/Fe increases from 2.06 to 2.15. While from the zone C to E, Ni cannot be detected and S/Fe decreases from 2.22 to 2.08. Powder X-ray diffraction (XRD) analysis in the micro zone shows obvious crystalline characteristics in the aggregates. Moving from the inside outwards, the maximum diffraction peak intensity of the (111) and (220) crystal planes of pyrite increases, and the crystallinity improves. The degree of change in the (111) plane is the most prominent Considering the theory of crystal growth along with the geologic features of the depositional environment where the spheroidal pyrite aggregates developed, we confirm that the spheroidal aggregates are the result of nano-micro crystalline gathering and growth occurring by the following sequence of processes: nano-crystalline nucleation and growth, gathering into a ball, oriented growth of microcrystals, continuous accumulation, and adjustment of grain boundaries. The formation of the spheroidal pyrite aggregates in the late Qiziqiao Formation of the Middle Devonian occurred in a neutral to weak alkaline and reductive sedimentary environment in the normal oxygen-rich shallow-water carbonate platform edge. The variations in the S/Fe ratio and crystallisation characteristics indicate that during pyrite crystal growth, the sulphur fugacity was high locally and rose constantly, the degree of supersaturation decreased locally and the growth environment was stable relatively.

Iron Pyrite Nanocrystal Inks: Solvothermal Synthesis, Digestive Ripening, and Reaction Mechanism

Colloidal iron pyrite nanocrystals (or FeS2 NC inks) are desirable as active materials in lithium ion batteries and photovoltaics and are particularly suitable for large-scale, roll-to-roll deposition or inkjet printing. However, to date, FeS2 NC inks have only been synthesized using the hot-injection technique, which requires air-free conditions and may not be desirable at an industrial scale. Here, we report the synthesis of monodisperse, colloidal, spherical, and phase-pure FeS2 NCs of 5.5 ± 0.3 nm in diameter via a scalable solvothermal method using iron diethyldithiocarbamate as the precursor, combined with a postdigestive ripening process. The phase purity and crystallinity are determined using X-ray diffraction, transmission electron microscopy, far-infrared spectroscopy, and Raman spectroscopy techniques. Through this study, a hypothesis has been verified that solvothermal syntheses can also produce FeS2 NC inks by incorporating three experimental conditions: high solubility of the precursor, efficient mass transport, and sufficient stabilizing ligands. The addition of ligands and stirring decrease the NC size and led to a narrow size distribution. Moreover, using density functional theory calculations, we have identified an acid-mediated decomposition of the precursor as the initial and critical step in the synthesis of FeS2 from iron diethyldithiocarbamate.

Phase-pure iron pyrite nanocrystals for low-cost photodetectors.

Earth-abundant iron pyrite (FeS2) shows great potential as a light absorber for solar cells and photodetectors due to their high absorption coefficient (>105 cm-1). In this paper, high-quality phase-pure and single crystalline pyrite nanocrystals were synthesized via facile, low-cost, and environment friendly hydrothermal method. The molar ratio of sulphur to iron and the reaction time play a crucial role in determining the quality and morphology of FeS2 nanocrystals. X-ray diffraction and high-resolution transmission electron microscopy confirm that phase-pure and single crystalline pyrite nanocrystals can be synthesized with high sulphur to iron molar ratio and sufficient reaction time. For the first time, a crystalline nanogap pyrite photodetector with promising photocurrent and UV-visible photoresponse has been fabricated. This work further demonstrates a facile route to synthesize high-quality FeS2 nanomaterials and their potential in optoelectronic applications.

Formation mechanisms of pyrite (FeS2) nano-crystals synthesized by colloidal route in sulfur abundant environment

Pyrite (FeS2) nano-crystals (NCs) were synthesized in an excess sulfur environment using a colloidal hot-injection method, and the phase change behavior of the iron sulfide compounds was investigated. As the growth time increased, the phase of the iron sulfide NCs transformed from mackinawite (FeS) via greigite (Fe3S4) to pyrite (FeS2). Thus, Fe3S4 phases was considered as intermediate precursors on the pathway of FeS2 phases in the reaction between FeS phases and excess sulfur. The elemental ratio of [S/Fe] increased from 1.1 to 2.1 during the phase change, and the shape of the NCs changed from a hexagonal nano-sheet (Fe3S4), via cubic (FeS2), to a cubic-hedral structure (FeS2). Strong absorption peaks in the UV–Vis spectra were observed in the FeS2 phase, and its optical band gap was estimated to be ∼0.9 eV, indicating the semiconducting nature of pyrite. Consequently, the synthesis of FeS2 in sulfur abundant environment was suitable method to acquire a pure semiconducting FeS2 phases. The reason was thought that the depletion of Fe-element after the formation of FeS2 phases led to the decrease of intermediate phases and the gradual changes from intermediate phases to FeS2 resulted in pure phases.

Surface thermal stability of iron pyrite nanocrystals: Role of capping ligands

Iron pyrite (FeS2) is a promising photovoltaic absorber material with a high natural abundance and low cost, but surface defects and low photoresponse inhibit sunlight energy conversion. The surface stability of pyrite FeS2 nanocrystals synthesized in oleylamine (OLA) with trioctylphosphine oxide (TOPO) as an additional capping ligand was investigated using Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction. Tunable laser exposure during Raman spectroscopy measurement was developed for convenient and systematic evaluation of the stability of FeS2 nanocrystals. The surface stability of 100–200nm diameter cubic nanocrystals with long-chain (OLA, TOPO) or small-molecule (pyridine) capping ligands was evaluated after high-intensity laser exposure as well as after thermal annealing in air and N2. While increasing surface coverage with OLA and TOPO capping ligands provided additional protection against oxidation, FeS2 nanocrystals capped with pyridine showed good stability at temperatures up to 200°C in air and 400°C in N2. These results provide greater understanding of the processing of nanocrystal-based iron pyrite thin films for photovoltaic applications.

Synthesis, characterization and optoelectronic properties of iron pyrite nanohusks

Poly-sized iron pyrite nanohusks with an average length of ~6nm were synthesized in ethanolamine which acts as a solvent and a surfactant at 210°C in a Schlenk flask. An X-ray diffraction pattern and Raman spectra show a cubic iron pyrite structure with prominent Raman peaks at the 339.5 and 378 positions, typical of cubic iron pyrite. UV–vis spectra show an increased band gap of 1.34eV due to quantum size effects. The synthesized semiconducting iron pyrite nanohusks owing to lighter weight and strong visible light coverage have advantages over large pyrite nanocrystals, since the larger particles usually sink down to the bottom on spin casting due to unavoidable gravity effects. When such nanohusks were applied in a bulk-heterojunction type solar cell with an n-type fullerene (PCBM), an efficiency of 0.23% was observed with a JSC of 1.4mA/cm−2, a VOC of 0.17V and a fill factor of 32. The morphology and optoelectronic properties of the synthesized nanohusks were elucidated by TEM, XRD, micro-Raman spectra, UV–vis, SEM, XPS, TEM-EDX and J–V techniques.

Optical and Electronic Properties of Pyrite Nanocrystal Thin Films: the Role of Ligands

Pyrite nanocrystals are currently considered as a promising material for large scale photovoltaic applications due to their non-toxicity and large abundance. While scalable synthetic routes for phase-pure and shape controlled colloidal pyrite nanocrystals have been reported, their use in solar cells has been hampered by the detrimental effects of their surface defects. Here, we report a systematic study of optical and electronic properties of pyrite nanocrystal thin films employing a series of different ligands varying both the anchor and bridging group. The effect of the ligands on the optical and electronic properties is investigated by UV-vis/NIR absorption spectroscopy, current voltage characteristic measurements and surface photovoltage spectroscopy. We find that the optical absorption is mainly determined by the anchor group. The absorption onset in the thin films shifts up to ∼100 meV to the red. This is attributed to changes in the dielectric environment induced by different anchors. The conductivity and photoconductivity, on the other hand, are determined by combined effects of anchor and bridging group, which modify the effective hopping barrier. Employing different ligands, the differential conductance varies over four orders of magnitude. The largest redshift and differential conductance are observed for ammonium sulfides and thiolated aromatic linkers. Pyridine and long chain amines, on the other hand, lead to smaller modifications. Our findings highlight the importance of surface functionalization and interparticle electronic coupling in the use of pyrite nanocrystals for photovoltaic devices.

Controlled colloidal synthesis of iron pyrite FeS2nanorods and quasi-cubic nanocrystal agglomerates

Earth-abundant and nontoxic pyrite iron disulfide (FeS2) is very promising for photovoltaic applications but the phase purity and the morphology of iron pyrite nanocrystals (NCs) have a significant impact on the solar cell performance. In this work, we systematically investigated reaction conditions and the local chemical environment on the phase purity and morphology of iron pyrite NCs synthesized via the hot injection method. By using different solvents to dissolve iron and sulfur agents, varying reactant concentrations, and adding trioctylphosphine oxide (TOPO) or 1,2-hexadecanediol (Diol) into the reaction solution, iron pyrite short, branched and chromosome-like rods were obtained with a diameter of ~10 nm and a length of ~20-30 nm as well as quasi-cubic NC agglomerates with a size of ~200 nm. Our experimental results show that the molar ratio of sulfur to iron and the reaction temperature are two critical factors in determining the crystalline phase of the synthesized materials. A mechanism involving the generation of H2S is proposed to explain the phase purity observed. The as-synthesized iron pyrite NCs can be dispersed well in chloroform, chlorobenzene, toluene, and hexane and thus are promising in solution-processable photovoltaic applications.

Solution-processed inverted solar cells using an inorganic bulk heterojunction of iron pyrite nanocrystals and cadmium selenide quantum dots with a polymeric hole-transport medium

Inverted solar cells were developed using a donor–acceptor (D–A) bulk heterojunction (BHJ) of iron pyrite nanocrystals (FeS2 NCs) and cadmium selenide quantum dots (CdSe QDs). The all-inorganic BHJ nanocomposites showed broad-range absorption and effective dynamics of charge dissociation and transfer through bi-continuous D–A interactions under a type II band-offset system. The developed solar cell, which contained an optimized ratio of FeS2–CdSe in the blend and a polymeric hole-transport layer between the photoactive layer and the anode electrode, showed a significantly enhanced photovoltaic efficiency. The long-term ambient stability of the inverted devices was better than that of conventional devices fabricated in this study, but was relatively lower than the air stability of other NC solar cells. Our findings suggest the potential of FeS2 NCs as an environmentally benign, earth-abundant material for solution-processed photovoltaic applications. The merits of an FeS2–CdSe D–A BHJ system with an inverted device architecture and its long-term stability are addressed.

Symmetry-Defying Iron Pyrite (FeS2) Nanocrystals through Oriented Attachment

Iron pyrite (fool's gold, FeS2) is a promising earth abundant and environmentally benign semiconductor material that shows promise as a strong and broad absorber for photovoltaics and high energy density cathode material for batteries. However, controlling FeS2 nanocrystal formation (composition, size, shape, stoichiometry, etc.) and defect mitigation still remains a challenge. These problems represent significant limitations in the ability to control electrical, optical and electrochemical properties to exploit pyrite's full potential for sustainable energy applications. Here, we report a symmetry-defying oriented attachment FeS2 nanocrystal growth by examining the nanostructure evolution and recrystallization to uncover how the shape, size and defects of FeS2 nanocrystals changes during growth. It is demonstrated that a well-controlled reaction temperature and annealing time results in polycrystal-to-monocrystal formation and defect annihilation, which correlates with the performance of photoresponse devices. This knowledge opens up a new tactic to address pyrite's known defect problems.

Ligand-Controlled Colloidal Synthesis and Electronic Structure Characterization of Cubic Iron Pyrite (FeS2) Nanocrystals

Iron pyrite (FeS2) is a promising photovoltaic absorber because of its Earth abundance, high optical extinction, and infrared band gap (Eg = 0.95 eV), but its use has been hindered because of the difficulty of phase pure synthesis. Pyrite phase purity is a paramount concern, as other phases of iron sulfide have undesirable electronic properties. Here we report the synthesis of phase pure iron pyrite nanocrystals with cubic morphology and a mean dimension of 80 nm. Control over the nanocrystal shape was achieved using an unusual ligand, 1-hexadecanesulfonate. The particles were characterized via synchrotron X-ray spectroscopy, indicating an indirect band gap of 1.00 ± 0.11 eV and a valence bandwidth of nearly 1 eV. Transmission electron microscopy from early reaction stages suggests a nucleation and growth mechanism similar to solution precipitation syntheses typical of metal oxide nanocrystals, rather than the diffusion-limited growth process typical of hot-injection metal chalcogenide nanocrystal syntheses.

Synthesis and Optoelectronic Properties of Pyrite (FeS&lt;SUB&gt;2&lt;/SUB&gt;) Nanocrystals Thin Films for Photovoltaic Applications

Synthesis and Optoelectronic Properties of Pyrite (FeS&lt;SUB&gt;2&lt;/SUB&gt;) Nanocrystals Thin Films for Photovoltaic Applications

Synthesis of iron pyrite nanocrystals utilizing trioctylphosphine oxide (TOPO) for photovoltaic devices

Iron pyrite nanocrystals with trioctylphosphine oxide (TOPO) were synthesized and characterized bearing in mind their use for photovoltaic devices. The nanocrystals were characterized by using optical absorption, X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The optical absorbance spectra exhibit large absorption in the visible and near infrared spectral range. Utilizing the X-ray diffraction, the FeS2 nanocrystals were found to have a face-centered cubic structure by comparing and matching the pattern to a data reference pattern. The SEM and TEM images indicate that the FeS2 nanocrystals exhibit face-centered cubic crystallographic structure.