Synthesis of Nanocrystalline FeS<sub>2</sub> with Increased Band Gap for Solar Energy Harvesting

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Somnath Middya, Animesh Layek, Arka Dey, Partha Pratim Ray. Synthesis of Nanocrystalline FeS₂ with Increased Band Gap for Solar Energy Harvesting . Journal of Materials Science & Technology, 2014, 30(8): 770-775 Copy to clipboard

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Synthesis of Nanocrystalline FeS₂ with Increased Band Gap for Solar Energy Harvesting

Somnath Middya, Animesh Layek, Arka Dey, Partha Pratim Ray^*

Department of Physics, Jadavpur University, Kolkata 700 032, India

* Corresponding author. Prof., Ph.D.; Tel.: t91 9475237259; Fax: t9133 24138917; E-mail address:partha@phys.jdvu.ac.in (P. P. Ray).

Abstract

In this paper, we have reported the synthesis of FeS₂ of higher band gap energy (2.75 eV) by using capping reagent and its successive application in organic–inorganic based hybrid solar cells. Hydrothermal route was adopted for preparing iron pyrite (FeS₂) nanoparticles with capping reagent PEG-400. The quality of synthesized FeS₂ material was confirmed by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, thermogravimetric analyzer, and Raman study. The optical band gap energy and electro-chemical band gap energy of the synthesized FeS₂ were investigated by UV–vis spectrophotometry and cyclic voltammetry. Finally band gap engineered FeS₂ has been successfully used in conjunction with conjugated polymer MEHPPV for harvesting solar energy. The energy conversion efficiency was obtained as 0.064% with a fill-factor of 0.52.

Keyword: Hydrothermal synthesis; FeS₂ nanoparticles; Optical characterization; Energy band gap

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1. Introduction

The FeS₂ in pyrite phase is an important material because of its environmental compatibility and high stability towards photo corrosion^{[ 1]}. It has attracted significant scientific interest and has numerous technological applications^{[ 2], [ 3]}. Owing to their large potential capacities in application of devices, iron–sulfur based materials have been extensively studied by Kirkeminde et al.^{[ 4]}. The photo-sensing behavior mainly depends on the absorbance and the direct band gap of the materials. The indirect band gap of FeS₂ was measured as 0.95 eV by Ennaoui et al., which is suboptimal for single junction photovoltaic application^{[ 5]}. To improve the band gap of pyrite FeS₂, enormous efforts have been made. By controlling the environmental conditions of reaction, it is possible to synthesize high quality FeS₂ nanoparticle with desired property. Improvement in absorbance of FeS₂ can be done by tuning the nanomorphology. FeS₂ nanoparticles with different morphology have been fabricated by using a variety of synthetic methods^{[ 6]}. Sun and Ceder studied and tried the technique to tune the band gap of FeS₂ by controlling the particle size^{[ 7]}. As it had been reported so far, there are various phases of FeS₂, such as mackinawite (tetragonal), troilite (hexagonal), pyrrhotite (monoclinic), smythite (hexagonal), pyrite (cubic), marcasite (orthorhombic) and greigite (cubic)^{[ 7]}. The solids consisting only of iron and sulfur are known to occur naturally at lower temperature (below 200 °C). The structural growth strongly depends upon the reaction temperature and the vapor pressure of the solvent. Wadia et al.^{[ 8]} reported that iron pyrite (FeS₂) is significantly attractive in both cost and availability for the application of thin film technology. Like FeS₂ there are very few nano-semiconducting materials, which can meet the large scale need, outside quantum confined systems^{[ 8]}. As the pyrite phase has more extensive stability in natural environment in spite of its lower band gap, the use of this phase is enormous. Unfortunately, the iron pyrite based solar energy harvesting devices have been plagued by performance problems. The science behind its underperformance is still not well understood. After hard research work and a prolonged study it is identified that the various phases of FeS₂ produce surface defects near the surface of thin film and grain boundaries that limit the open circuit voltage of the photovoltaic devices. Ennaoui et al. reported pyrite single crystal based photo electrochemical cells, which show low open circuit voltage of 187 mV and fill-factor (FF) of 0.5^{[ 9]}. The phase purity was attributed to low open circuit voltage, which was reported by Thomas et al.^{[ 10]}. Ganta et al.^{[ 11]} successively synthesized superstrate type FeS₂ and CdS ink-based solar cell with efficiency of 0.03% and open circuit voltage ( V_oc) of 565 mV. Several recent publications exhibited that successful and robust synthesis of pyrite nanocrystals and many efforts have been directed toward exploring their optoelectronic applications^{[ 12], [ 13], [ 14], [ 15], [ 16]}. Most recently (in the year 2012) Kirkeminde et al. reported inorganic solar cell based on ITO/PEDOT:PSS/(TFB) poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(4-s-butylphenyl)) diphenylamine)]/FeS₂:CdS/Al structure, which showed more promising results with a PCE of 1.1% and V_oc of 0.79 V^{[ 17]}, but the absorption and charge transportation highly depends on the CdS quantum dot, rather FeS₂. Bi et al.^{[ 14]} synthesized FeS₂ NCs with improved stability in air and observed a photo response in an ITO/FeS₂ NC/Al device, but the result is not upto the mark. Moreover, not surprisingly, no rectification behavior was observed, as the pyrite formed ohmic contacts at the ITO (indium tin oxides) and aluminum interfaces. Despite these recent works and renewed interest in pyrite FeS₂ over the past several years, no high performance device has been made yet based on this material. Further investigation on the fundamental properties of pyrite FeS₂ and deployment in alternative device architectures are required to explore the potential of pyrite FeS₂ in photovoltaics.

Here we have studied a different technique to improve the band gap energy of FeS₂ by changing the architectural growth. Capping reagent has been introduced to influence the vapor pressure of the solution, which can effectively control the morphology via controlling the growth rate. The optical absorption of the synthesized material was studied by UV–vis absorption spectroscopy. Depending upon the morphological growth, energy absorption of as-synthesized iron pyrite was noticed as very low compared to other inorganic semiconductors. The optical band gap energy estimated from UV–vis absorption data was significantly improved. This fact was in agreement with the absorbing behavior of iron pyrite, for its modified architecture and epitaxial growth. The electrochemical band gap energy was calculated from oxidation (corresponding to valence band) and reduction (corresponding to conduction band) states with the help of cyclic voltammetry (CV). Thermal stability of the FeS₂ nanoparticle was studied with thermogravimetric analyzer (TGA). It is obvious that by controlling the growth of morphology with chemical surfactant, the band gap would successively tune up for application in high temperature semiconducting electronic devices. Thus our synthesized semiconducting material with higher band gap and thermal stability can be applied in photovoltaics at high temperature. It is noteworthy that it has still remained as a challenging unexplored arena for the researchers. In the fore step we have fabricated ITO/PEDOT:PSS/MEH-PPV:FeS₂/Al based hybrid solar cell and characterized the device to estimate different cell parameters. The polymer MEHPPV has a wide research application for its higher absorption with band gap energy of 2.2 eV, as a semiconducting donor polymer in fabrication of efficient thin film hybrid solar cell. This was the early challenge to harvest solar energy by mostly abundant iron-pyrite conjugated with MEHPPV. The subject still remains unexplored. The synthesized FeS₂ of higher band gap energy with corresponding energy levels demonstrates the successive charge transportation phenomena from MEHPPV donor to FeS₂ acceptor and also explains the improvement of open circuit voltage of the device. This is the uniqueness of this work.

2. Experimental

2.1. Experimental reagents

Hydrated ferric chloride (FeCl₃·6H₂O), hydrated sodium sulfide (Na₂S·9H₂O), ammonium hydroxide (NH₄OH), ethanol, chloroform and polyethylene glycol (PEG-400) of AR grade were procured from Merck. Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV), poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and sulfur powder were purchased from Sigma Aldrich. All these chemicals were used without further purification.

2.2. Synthesis of iron-pyrite nanoparticles

In this work FeS₂ nanoparticles were synthesized by adopting hydrothermal synthesis to curtail the manufacturing cost^{[ 18]}. 20 ml 0.1 mol/L ferric chloride aqueous solution was prepared to mix with 20 ml 0.1 mol/L Na₂S aqueous solution. The mixture was stirred for 30 min with the help of magnetic stirrer. By maintaining the pH value of the solution within 6–7, NH₄OH aqueous solution was added drop-wise to the mixture. A black–brown precipitate was observed, and 10 ml PEG-400 was added. 0.2 mg sulfur powder was mixed simultaneously with the solution and was sonicated for 24 h. The desired mixture was then transferred into a linear Teflon autoclave to be heated at 120 °C for 2 days. Then the nanoparticles were collected by washing with ethanol and distilled water repeatedly by centrifuge technique.

2.3. Device fabrication

Before device fabrication, the solutions of MEHPPV and synthesized FeS₂ nano-particle were prepared separately in chloroform with concentration of 10 mg/mL and 2 mg/mL, respectively. Solutions were mixed at appropriate weight ratio under vigorous stirring by magnetic stirrer for 2 h to get the desired mixture. As a buffer transparent layer, PEDOT:PSS was spun on the patterned and pre-cleaned ITO substrate (cleaned with acetone, ethanol and de-ionized water repeatedly under ultra-sonic bath) at 1200 r/min for 2 min and then dried at 100 °C. The active layers of blended solution of MEH-PPV:FeS₂ composite was prepared via spin coating at 2000 r/min for 2 min in open atmosphere with the help of SCU-2007 spin coating unit. Solvent evaporation has been done by heating the samples at 100 °C for 10 min under vacuum oven. Thereafter, aluminum electrode as back contact was deposited on to the active film with shadow mask by thermal evaporation technique with the help of 12A4D HHV vacuum coating unit.

3. Characterization

The characterization of blackish FeS₂ nanopowder was done by recording powder X-ray diffraction (XRD) spectra with the help of Bruker D8-X-ray Diffractometer, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) of JEOL make. To investigate the functional groups, which are responsible for homogenous dispersion in chloroform medium, Fourier transform infrared (FTIR) spectra were recorded with the help of FTIR-8400S Spectrophotometer of Shimadzu. The thermal stability of the sample was measured with DTG-60 thermogravimetric and differential thermal analyzer of Shimadzu. The sample was heated at a rate of 10 °C min^-1 in a nitrogen atmosphere starting from 50 to 800 °C. The electrochemical measurements were carried out using a Gamry reference 750 potentiostat in a three-electrode configuration. CV was performed using a conventional three-electrode system. The working electrode was a photocatalyst powder-modified glassy carbon electrode (GCE) (3 mm diameter), the reference electrode was an Ag/AgCl (in 3 mol/L NaCl) electrode, and the counter electrode was a platinum wire. The electrochemical band gap energy of the material was measured from CV data and the optical band gap energy was evaluated from UV–VIS absorption data, recorded with the help of 2401PC Shimadzu Spectrophotometer. To study the energy quenching of the composite, the photoluminescence spectra were recorded with the help of Cary Eclipse Fluorescence Spectrophotometer from Varian. The current density vs voltage characteristic of the device was measured with Keithley 2400 sourcemeter interfaced with PC.

4. Results and Discussion

Fig. 1 represents the XRD spectra of the synthesized material. The XRD peaks from each responsible Bragg's ( hkl) planes for diffraction were recorded as (111), (200), (210), (211), (220), (221), (311) and (222) at 2 θ = 28.5, 33, 37, 40.7, 47.4, 51.9, 56.3, and 58.9 deg, respectively, which is related to FeS₂ pyrite (cubic structure) with phase purity^{[ 13]}. This phase is approved by JCPDS card no. 42-1340. Few extra peaks may be due to the attenuation and the presence of noise. Analysis of the XRD pattern using Scherrer's broadening equation, estimates the particle size^{[ 19]}. From XRD spectrum by measuring the broadening of intensity at half maxima in radian and considering wavelength ( λ) = 0.154 nm (Cu Kα), the particle size of the material was evaluated with the auxiliary equation λ/ Bcos θ as 19 nm, where B represents the broadening constant and θ is the Bragg's angle.

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	Fig. 1. XRD spectra of FeS₂ nanoparticles.

Fig. 2 and Fig. 3 represent FE-SEM and TEM images of the as-synthesized FeS₂. These FE-SEM and TEM images exhibited that the size of the particles are in nano range (10–100 nm). The coagulations of the particles were observed from these electron microscopic imaging. The morphology of the particles is indistinguishable, which may be due to the coagulations of the nanoparticles. This is crudely related with the chain length of the capping reagent and the solution vapor pressure.

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	Fig. 2. FE-SEM image of FeS₂ nanoparticles.

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	Fig. 3. TEM image of FeS₂ nanoparticles.

Fig. 4 represents FTIR spectroscopy of FeS₂ nanoparticles. This spectrum exhibited O–H stretching as peak at 3559 cm^-1 and a broad peak centered around 3127 cm^-1. The absorption near 1402 cm^-1 corresponds to the C–H bending vibration which came from the capping reagent (PEG-400). In addition, the band at 1124 cm^-1 represented the asymmetric S–O stretching of the sulfate species, while the peak at 610 cm^-1 was the consequence of the disulfide stretching (S–S)^{[ 20]}.

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	Fig. 4. FTIR spectra of FeS₂ nanoparticles.

To study the chemical bonds and symmetry of molecules the vibrational information has been gathered from Raman spectroscopy. The active modes of Raman spectra consist of a symmetric mode ( A_g), a doubly degenerate ( E_g), and three triply degenerate modes. Fig. 5 represents the Raman spectra of FeS₂ nanoparticle, recorded in the wave number range from 200 to 1000 cm^-1. In this spectra sharp peaks were observed at 339 and 376 cm^-1, which are the characteristic active modes for FeS₂ corresponding to the S₂ libration ( E_g) and in phase stretching vibration of S–S dimer ( A_g), respectively. In the E_g mode, the S atoms are displaced perpendicularly to the dimer axes. The peak at 497 cm^-1 corresponds to the coupled libration and stretching ( T_g) modes or their combination^{[ 21], [ 22]}. The above peaks exhibit the pyrite cubic structure^{[ 23]}.

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	Fig. 5. Raman spectra of FeS₂ nanoparticles.

Fig. 6 represents the thermal degradation of mass with decomposition, which was recorded with increasing temperature starting from 50 to 800 °C by TGA. This TGA curve shows a drastic weight loss at around 50–250 °C. It may be caused by dehydration of the hydroxyls. Thereafter the degradation was not observed till 600 °C, which indicates the thermal stability of the sample. Therefore, it is obvious from this graph that FeS₂ is thermally stable up to 600 °C. After that the sample started to be decomposed sharply. Finally the sample was decomposed to 25% of its initial mass at temperature 800 °C. It may be due to the dissociation of FeS₂ into iron oxide. The important thing is to be noted that the high thermal constancy of FeS₂, dignified the material for the application in high temperature environment (i.e., greater than room temperature).

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	Fig. 6. TGA curve of FeS₂ nanoparticles.

The UV–vis absorption spectra of FeS₂ nanoparticle, dispersed in DMF solution is given in the inset of Fig. 7. These data were analyzed with Tauc's equation and considering the intercept of the sharp linear plot ( αhν)² vs incident photon energy ( hν) at incident energy axis. The direct optical band gap energy of the nanomaterial at room temperature was measured as 2.75 eV ( Fig. 7). With these UV–vis spectral data considering Davis and Mott's equation, the curve α (absorption coefficient) vs hν (incident photon energy) was plotted to estimate direct optical band gap energy of FeS₂ nanomaterial ( Fig. 8). From this plot, the direct band gap energy of the nanomaterial was calculated as 2.74 eV, which is not much different from the value estimated by Tauc's equation. The direct band gap of FeS₂, reported so far is in the range from 0.7 to 2.6 eV^{[ 24]}. In this study, the effective direct band gap at room temperature of the nanomaterial, as measured from Tauc's and Davis–Mott's equation is appreciably high. It might be due to the epitaxial growth of the nanocrystal during hydrothermal synthesis^{[ 25], [ 26], [ 27]}, or due to the Burstein–Moss effect^{[ 28], [ 29]}. According to Burstein–Moss effect, depending upon the morphological growth of nanoparticles the absorption edge is pushed to higher energies, as a result of all states close to the conduction band being populated.

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2 nanoparticles. '>	Fig. 7. Tauc's plot and band gap of FeS₂ nanoparticles.

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2 nanoparticles. '>	Fig. 8. Devis-Mott's plot and band gap of FeS₂ nanoparticles.

Fig. 9 shows the cyclic voltammogram of dispersed FeS₂ nanoparticles. The voltammogram shows an oxidation peak, i.e., the ionization potential at approximately +1.74 V and a reduction peak, i.e., the electron affinity at about -0.99 V. In order to estimate the electrochemical band gap energy, the conduction and valence band energy ( E_CB and E_VB) were calculated with the help of following equations

and

as E_CB = -3.15 eV and E_VB = -5.88 eV, where E_ox and E_red are the onset potentials of the oxidation and reduction relative to an Ag reference electrode, respectively. The value 4.14 eV represents the difference between the vacuum level potential of the normal hydrogen electrode and the potential of the Ag/AgNO₃ electrode. Calculating the difference Δ E = E_CB - E_VB^{[ 30]}, the energy band gap of FeS₂ was estimated as 2.73 eV.

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	Fig. 9. Cyclic voltammetry (CV) analysis of FeS₂ nanoparticles.

Fig. 10 represents the photoluminescence (PL) spectra of MEHPPV and MEHPPV:FeS₂ composite in chloroform medium, in the wavelength range from 450 to 750 nm. The figure shows that for the composite, PL excitation peak has been shifted from 558 to 565 nm. The deviation of excitation peak of composite from MEHPPV in chloroform medium indicates the energy quenching with red shift. The PL intensity is significantly reduced to 0.3 times of the value of MEHPPV during formation of composite with FeS₂. The static energy quenching of MEHPPV with incorporation of FeS₂ nanoparticle was observed distinctly in Fig. 9. Thus it is obvious that in MEHPPV:FeS₂ composite, FeS₂ nanoparticle acts as a semiconducting acceptor. The PL quenching is the evidence for exciton dissociation. When the photogenerated excitons are dissociated, the probability for recombination should be significantly reduced. This is the ultrafast electron transfer phenomena from donor to acceptor and it is expected to increase the exciton dissociation efficiency in photovoltaic devices^{[ 31] and [ 32]}.

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	Fig. 10. Photoluminesence spectra of MEHPPV and MEHPPV:FeS₂ composite.

Fig. 11 represents the current density–voltage ( J– V) characteristic of the device with structure ITO/PEDOT:PSS/MEHPPV:FeS₂/Al. The effective diameter of each cell is 2 mm. The J– V characteristic of the device was recorded under the illumination of white light with incident power density of 80 mW cm^-2. From these characteristic curves the short circuit current density ( J_sc) and open circuit voltage ( V_oc) were measured as 0.13 mA cm^-2 and 0.72 V, respectively. The maximum power, maximum voltage, energy conversion efficiency, and fill-factor were calculated as 0.049 mW cm^-2, 0.5 V, 0.064% and 0.52 for the device, sequentially ( Table 1). The series and shunt resistances ( R_s and R_sh) of the device, as measured from J– V curve are 53 Ω and 2.13 kΩ, respectively. From CV analysis of FeS₂ by knowing the positions of energy levels, the exciton dissociations and charge transportation path way from donor polymer (MEHPPV), with HOMO energy -5.1 eV and lowest unoccupied molecular orbital (LUMO) energy at -2.7 eV, to acceptor (FeS₂) can be explained. The energy band diagram ( Fig. 12) approved the concerned motivation and experimental effort consecutively. Thus newly found FeS₂ with higher band gap energy can be a good candidate for solar energy harvesting. To improve the efficiency of the device the thicknesses of different layers should be optimized along with material synthesis conditions.

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	Fig. 11. Density–voltage ( J– V) characteristic curve of ITO/PEDOT:PSS/MEHPPV:FeS₂/Al device.

Table 1. Characteristics data of the device

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	Fig. 12. Energy band diagram for the array ITO/PEDOT:PSS/MEHPPV:FeS₂/Al with charge transportation path way.

5. Conclusion

In this experimental study, the energy band gap of iron pyrite (FeS₂) nanoparticle was successively improved to be 2.74 eV by improving the synthesis technique with capping reagent. The morphological growth of nanoparticle with capping reagent PEG-400 improved the surface to volume ratio and thermal stability of semiconducting FeS₂. By incorporating synthesized FeS₂ nanoparticle with MEHPPV we have succeeded to harvest solar energy. The energy conversion efficiency can be improved further by fabricating the device under inert atmosphere within glove box. Thus the non-toxic FeS₂ semiconducting nanoparticle with higher band gap energy can be applied for harvesting solar energy.

Acknowledgements

This work was supported by University Grants Commission (UGC), Govt. of India under project 39-508/2010 (SR). The authors acknowledge Madhusudan Nandy of Department of Chemistry, Jadavpur University and Priyanka Das of Department of Chemistry, West Bengal State University, Barasat for their valuable advice and enormous technical assistance.

The authors have declared that no competing interests exist.

作者声明: 无竞争性利益关系

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2011

0.402

0.0

... IntroductionThe FeS₂ in pyrite phase is an important material because of its environmental compatibility and high stability towards photo corrosion^[1] ...

2009

8.238

0.0

Wadia

, Y.

, S.

Gul

, S.

Volkman

, J.

Guo

, A. P.

Alivisatos

;Chem. Mater. , 21 (2009), pp. 2568–2570

† Department of Chemistry ‡ Energy & Resources Group § Department of Electrical Engineering and Computer Sciences ∥ Department of Materials Science and Engineering University of California, Berkeley, California 94720 ⊥ Advanced Light Source # Materials Science Division Lawrence Berkeley National Laboratory, Berkeley, California 94720 ▽ These authors contributed equally to this work.

... It has attracted significant scientific interest and has numerous technological applications^{[2], [3]} ...

1985

2.588

0.0

... It has attracted significant scientific interest and has numerous technological applications^{[2], [3]} ...

2012

5.008

0.0

Kirkeminde

, B. A.

Ruzicka

, R.

Wang

, S.

Puna

, H.

Zhao

, S.

Ren

;ACS Appl. Mater. Interfaces, 4 (2012), pp. 1174–1177

† Department of Chemistry, ‡ Department of Physics and Astronomy, University of Kansas , Lawrence, KS, USA 66045. *E-mail: shenqiang@ku.edu .

There is a growing interest in the earth abundant and nontoxic iron disulfide (FeS 2 ) photovoltaic materials. Here, we report the synthesis of FeS 2 nanoplates with different spectral features which we have associated with thicknesses and crystallization. The structure and crystalline order of ultrathin FeS 2 nanoplates have a strong influence on the carrier lifetime, electronic and optical properties. We demonstrate that two-dimensional FeS 2 nanoplates show great promise for fabrication of hybrid bulk heterojunction solar cells. This opens up a host of applications of these materials as inexpensive solar cells and photocatalysts.

... ^[4] ...

1993

0.0

Ennaoui

, S.

Fiechter

, C.

Pettenkofer

, N.

Alonso-Vante

, K.

Buker

, M.

Bronold

, C.

Hopfner

, H.

Tributsch

;Sol. Energy Mater. Sol. Cells, 29 (1993), pp. 289–370

... , which is suboptimal for single junction photovoltaic application^[5] ...

2010

1.253

0.0

... FeS₂ nanoparticles with different morphology have been fabricated by using a variety of synthetic methods^[6] ...

2011

0.0

Sun

, G.

Ceder

;Phys. Rev. B, 84 (2011), p. 245211

... Sun and Ceder studied and tried the technique to tune the band gap of FeS₂ by controlling the particle size^[7] ...

... As it had been reported so far, there are various phases of FeS₂, such as mackinawite (tetragonal), troilite (hexagonal), pyrrhotite (monoclinic), smythite (hexagonal), pyrite (cubic), marcasite (orthorhombic) and greigite (cubic)^[7] ...

2009

5.228

0.0

Wadia

, A. P.

Alivisatos

, D. M.

Kammen

;Environ. Sci. Technol. , 43 (2009), pp. 2072–2077

Energy and Resources Group, University of California, Berkeley, California 94720-3050, Department of Chemistry, University of California, Berkeley, California 94720, Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Materials Science and Engineering, University of California, Berkeley, California 94720, Goldman School of Public Policy, University of California, Berkeley, California 94720-3050, and Renewable and Appropriate Energy Laboratory, University of California, Berkeley, California 94720-3050 * Corresponding author phone: 510-642-1640 ; e-mail: kammen@berkeley.edu .,† Energy and Resources Group, University of California. ,‡ Department of Chemistry, University of California. ,§ Lawrence Berkeley National Laboratory. ,∥ Department of Materials Science and Engineering, University of California. ,⊥ Goldman School of Public Policy, University of California. ,# Renewable and Appropriate Energy Laboratory, University of California.

Solar photovoltaics have great promise for a low-carbon future but remain expensive relative to other technologies. Greatly increased penetration of photovoltaics into global energy markets requires an expansion in attention from designs of high-performance to those that can deliver significantly lower cost per kilowatt-hour. To evaluate a new set of technical and economic performance targets, we examine material extraction costs and supply constraints for 23 promising semiconducting materials. Twelve composite materials systems were found to have the capacity to meet or exceed the annual worldwide electricity consumption of 17 000 TWh, of which nine have the potential for a significant cost reduction over crystalline silicon. We identify a large material extraction cost (cents/watt) gap between leading thin film materials and a number of unconventional solar cell candidates including FeS 2 , CuO, and Zn 3 P 2 . We find that devices performing below 10% power conversion efficiencies deliver the same lifetime energy output as those above 20% when a 3/4 material reduction is achieved. Here, we develop a roadmap emphasizing low-cost alternatives that could become a dominant new approach for photovoltaics research and deployment.

... ^[8] reported that iron pyrite (FeS₂) is significantly attractive in both cost and availability for the application of thin film technology ...

... Like FeS₂ there are very few nano-semiconducting materials, which can meet the large scale need, outside quantum confined systems^[8] ...

1986

2.588

0.0

... 5^[9] ...

0.0

... ^[10] ...

1447

0.0

... ^[11] successively synthesized superstrate type FeS₂ and CdS ink-based solar cell with efficiency of 0 ...

2009

3.842

0.0

Y. Y.

Lin

, D. Y.

Wang

, H. C.

Yen

, H. L.

Chen

, C. C.

Chen

, C. M.

Chen

, C. Y.

Tang

, C. W.

Chen

;Nanotechnology, 20 (40) (2009), p. 405207

cjchen@ntnu.edu.tw chunwei@ntu.edu.tw 1 Department of Materials Science and Engineering, National Taiwan University, Taipei106,Taiwan 2 Department of Chemistry, National Taiwan Normal University, Taipei 116,Taiwan 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106,Taiwan 4 Fortune Institute of Technology, Kaohsiung 831,Taiwan 5 Instrumentation Center, National Taiwan University, Taipei 106,Taiwan

A polymer solar cell based on poly(3-hexylthiophene) (P3HT)/iron disulfide (FeS 2 ) nanocrystal (NC) hybrid is presented. The FeS 2 NCs of 10 nm in diameter were homogeneously blended with P3HT to form an active layer of a solar cell. An extended red light harvesting up to 900 nm resulting from the NCs in the device has been demonstrated, compared to a typical absorption edge of 650 nm of a pristine P3HT. The environmentally friendly and low-cost FeS 2 NCs can be used as a promising candidate for an acceptor in the polymer solar cell device application with an enhanced photovoltaic response in the extended red light region.

... Several recent publications exhibited that successful and robust synthesis of pyrite nanocrystals and many efforts have been directed toward exploring their optoelectronic applications ^{[12], [13], [14], [15], [16]} ...

2011

10.677

0.0

Puthussery

, S.

Seefeld

, N.

Berry

, M.

Gibbs

, M.

Law

;J. Am. Chem. Soc. , 133 (2011), pp. 716–719

Department of Chemistry and Department of Chemical Engineering and Materials Science, University of California, Irvine , California 92697, United States matt.law@uci.edu

Iron pyrite (FeS 2 ) is a promising earth-abundant semiconductor for thin-film solar cells. In this work, phase-pure, single-crystalline, and well-dispersed colloidal FeS 2 nanocrystals (NCs) were synthesized in high yield by a simple hot-injection route in octadecylamine and then were subjected to partial ligand exchange with octadecylxanthate to yield stable pyrite NC inks. Polycrystalline pyrite thin films were fabricated by sintering layers of these NCs at 500−600 °C under a sulfur atmosphere.

... 9 deg, respectively, which is related to FeS₂ pyrite (cubic structure) with phase purity ^[13] ...

2011

13.025

0.0

, Y. B.

Yuan

, C. L.

Exstrom

, S. A.

Darveau

, J. S.

Huang

;Nano Lett. , 11 (2011), pp. 4953–4957

Department of Mechanical and Materials Engineering, University of Nebraska—Lincoln , Lincoln, Nebraska 68588, United States Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083, People’s Republic of China Nebraska Center for Materials and Nanoscience, University of Nebraska—Lincoln , Lincoln, Nebraska 68583-0298, United States Department of Chemistry, University of Nebraska at Kearney , Kearney, Nebraska 68849-1150, United States E-mail: jhuang2@unl.edu .

Iron pyrite (FeS 2 ) is a naturally abundant and nontoxic photovoltaic material that can potentially make devices as efficient as silicon-based ones; however existing iron pyrite photovoltaic devices contain thermodynamically unstable FeS 2 film surfaces that lead to low open circuit voltages. We report the rational synthesis of phase pure, highly crystalline cubic FeS 2 nanocrystals (NCs) using a trioctylphosphine oxide (TOPO) assisted hot-injection method. The synthesized pyrite NC films have excellent air stability over one year. In contrast, obvious surface decomposition was observed on the surface of FeS 2 NCs synthesized without TOPO. A high carrier mobility of 80 cm 2 /(V s) and a strong photoconductivity were observed for the first time for pyrite films at room temperature. Our results indicate that TOPO passivates both iron and sulfur atoms on FeS 2 NC surfaces, efficiently inhibiting surface decomposition.

... ^[14] synthesized FeS₂ NCs with improved stability in air and observed a photo response in an ITO/FeS₂ NC/Al device, but the result is not upto the mark ...

2012

14.829

0.0

D. Y.

Wang

, Y. T.

Jiang

, C. C.

Lin

, S. S.

, Y. T.

Wang

, C. C.

Chen

, C. W.

Chen

;Adv. Mater. , 24 (2012), pp. 3415–3420

1 Department of Materials Science and Engineering, National Taiwan University, Taipei, 106, Taiwan 2 Department of Chemistry, National Taiwan Normal University, Taipei, 116, Taiwan 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan * Department of Chemistry, National Taiwan Normal University, Taipei, 116, Taiwan

2011

0.0

L. P.

, S.

Lany

, R.

Kykyneshi

, V.

Jieratum

, R.

Ravichand ran

, B.

Pelatt

, E.

Altschul

, H. A. S.

Platt

, J. F.

Wager

, D. A.

Keszler

, A.

Zunger

;Adv. Energy Mater. , 1 (2011), pp. 748–753

1 Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon 97331-4003, USA 2 School of Electrical Engineering and Computer Science, Oregon State University, 1148 Kelley Engineering Center, Corvallis, Oregon 97331-5501, USA 3 National Renewable Energy Laboratory, Golden, Colorado 80401, USA * Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon 97331-4003, USA.

2012

6.233

0.0

... 79 V ^[17], but the absorption and charge transportation highly depends on the CdS quantum dot, rather FeS₂ ...

2007

1.674

0.0

Feng

, X.

, W.

, C.

Jiang

, C.

Wan

;Ionics, 13 (2007), pp. 375–377

Nanocrystalline FeS 2 cathode material of lithium cell was synthesized from cheap materials of FeSO 4 , Na 2 S 2 O 3 , and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized, about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS 2 material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative effect on the electrochemical performance of the material. The synthetic FeS 2 showed a significant improvement of electrochemical performance for Li/FeS 2 cells.

1.Tsinghua University Institute of Nuclear and New Energy Technology 100084 Beijing People’s Republic of China

... Synthesis of iron-pyrite nanoparticlesIn this work FeS₂ nanoparticles were synthesized by adopting hydrothermal synthesis to curtail the manufacturing cost^[18] ...

1918

0.0

... Analysis of the XRD pattern using Scherrer's broadening equation, estimates the particle size ^[19] ...

1999

0.0

J. M.

Philias

, B.

Marsan

;Electrochem. Acta, 44 (1999), pp. 2351–2363

... S)^[20] ...

2012

0.0

... The peak at 497 cm^-1 corresponds to the coupled libration and stretching (T_g) modes or their combination ^{[21], [22]} ...

2010

2.771

0.0

M. Y. C.

Teo

, S. A.

Kulinich

, O. A.

Plaksin

, A. L.

Zhu

;J. Phys. Chem. A. , 114 (2010), pp. 4173–4180

Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada V6T 1Z1, Department of Applied Sciences, University of Quebec, Saguenay, PQ, Canada G7H 2B1, Leypunsky Institute for Physics and Power Engineering, Obninsk, Kaluga Region, Russia 249033, and Obninsk State Technical University for Nuclear Power Engineering, Obninsk, Kaluga Region, Russia 249040 * Corresponding authors. E-mail: plax@mail.ru (O.A.P.); researchman12001@yahoo.com (A.L.Z.).,† University of British Columbia. ,‡ University of Quebec. ,§ Leypunsky Institute for Physics and Power Engineering. ,∥ Obninsk State Technical University for Nuclear Power Engineering.

The conversions of NiAs-type structures of transition metal chalcogenides (FeS and CoSe) to pyrite-type structures of dichalcogenides (FeS 2 and CoSe 2 , respectively) under irradiation by HeNe laser (wavelength, 632.8 nm; intensity, 6 × 10 4 W/cm 2 ) have been investigated using Raman spectroscopy. The laser-induced conversions give rise to Raman peaks corresponding to vibrations of S−S or Se−Se bonds of respective pyrite structures. The results are of interest for the characterization and fabrication of pyrite-like structures necessary for applications as oxygen reduction reaction catalysts. Material modifications at the micrometer and submicrometer levels are attainable. The structural conversions are accompanied by self-polymerization of excess chalcogen. Extended laser irradiation (>500 s) in air induces the substitution of chalcogen (S or Se) by oxygen in the chalcogenide materials and the subsequent formation of transition metal (Fe or Co) oxides. Excess chalcogen appears to prevent further oxidation. The article also presents conditions necessary to avoid laser-induced structural changes and oxidation of metal chalcogenide materials during Raman measurements.

... The peak at 497 cm^-1 corresponds to the coupled libration and stretching (T_g) modes or their combination ^{[21], [22]} ...

2013

6.378

0.0

... The above peaks exhibit the pyrite cubic structure ^[23] ...

1990

2.588

0.0

... 6 eV ^[24] ...

2006

1.982

0.0

Masset

, J. Y.

Poinso

, J. C.

Poignet

;J. Thermal Anal. Calorim. , 83 (2006), pp. 457–462

The thermal decomposition of FeSO 4 ·6H 2 O was studied by mass spectroscopy coupled with DTA/TG thermal analysis under inert atmosphere. On the ground of TG measurements, the mechanism of decomposition of FeSO 4 ·6H 2 O is: i) three dehydration steps

1.Commissariat l'Energie Atomique, Centre d'Etude du Ripault, Monts France 37260 Monts France 37260 2.ASB - Aerospatiale Batteries, Allée Sainte Hélène Bourges France BP 16 18021 Bourges France BP 16 18021 3.Laboratoire d'Electrochimie et de Physicochimie des Matériaux et Interfaces (LEPMI) Saint Martin d'Hères, France BP 75 38402 1130 rue de la Piscine Saint Martin d'Hères, France BP 75 38402 1130 rue de la Piscine

... It might be due to the epitaxial growth of the nanocrystal during hydrothermal synthesis ^{[25], [26], [27]}, or due to the Burstein#cod#x02013 ...

1990

1.534

0.0

I. J.

Ferret

, D. M.

Nevskaia

, C.

de las Heras

, C.

Sanchez

;Solid State Commun. , 74 (1990), pp. 913–916

... It might be due to the epitaxial growth of the nanocrystal during hydrothermal synthesis ^{[25], [26], [27]}, or due to the Burstein#cod#x02013 ...

1989

4.63

0.0

Smestad

, A.

da Silva

, H.

Tributsch

, S.

Fiechter

, M.

Kunst

, N.

Mezziani

, M.

Birkholz

;Sol. Energy Mat. , 18 (1989), pp. 299–313

... It might be due to the epitaxial growth of the nanocrystal during hydrothermal synthesis ^{[25], [26], [27]}, or due to the Burstein#cod#x02013 ...

1988

1.838

0.0

Liu

, C.

Pettenkofer

, H.

Tributsch

;Surf. Sci. , 204 (1988), pp. 537–554

... Moss effect ^{[28], [29]} ...

1985

0.0

Sato

;Prog. Cryst. Growth Charact. , 11 (1985), pp. 109–154

... Moss effect ^{[28], [29]} ...

2011

0.0

... E = E_CB - E_VB^[30], the energy band gap of FeS₂ was estimated as 2 ...

2003

1.032

0.0

Chakraborty

, G.

Datta

, K.

Ghatak

;Phys. Scripta, 68 (2003), pp. 368–377

1 Department of Electronics and Electrical Communication Engineering, Indian Institute of Technology, Kharagpur, 721302, India 2 Semiconductor Device Laboratory, Department of Electronic Science, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta, 700 009, India

We study the effective electron mass at the Fermi-level on the basis of a newly formulated electron energy spectrum for heavily doped non-parabolic III–V semiconductors forming band-tails, taking n-InSb as an example. The investigation on the mass includes both the presence and absence of band-tailing states, in parabolic and non-parabolic energy band structures, respectively. The effective mass exists in the forbidden region, which is impossible without band-tailing effects. The analyses have been carried out for the Fermi-energy and other entities, like screening length and impurity screening potential, respectively. The values of the effective mass with band-tailing states are found much less as compared with in the absence of band-tails. The well-known results for unperturbed two-band model of Kane have also been obtained from our generalized analysis under certain limiting conditions.

... This is the ultrafast electron transfer phenomena from donor to acceptor and it is expected to increase the exciton dissociation efficiency in photovoltaic devices^{[31] and [32]} ...

2003

1.578

0.0

... This is the ultrafast electron transfer phenomena from donor to acceptor and it is expected to increase the exciton dissociation efficiency in photovoltaic devices^{[31] and [32]} ...