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

Available online at ScienceDirect

ScienceDirectJ. Mater. Sci. Technol., 2014, -(-), 1e6

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[Manuscript received June 21, 2013, in revised form August 16, 2013, Available online xxx]

* Corresp33 24131005-03JournalLimited.http://dx

Please

In this paper, we have reported the synthesis of FeS2 of higher band gap energy (2.75 eV) by using cappingreagent and its successive application in organiceinorganic based hybrid solar cells. Hydrothermal route wasadopted for preparing iron pyrite (FeS2) nanoparticles with capping reagent PEG-400. The quality ofsynthesized 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 investigatedby UVevis spectrophotometry and cyclic voltammetry. Finally band gap engineered FeS2 has beensuccessfully used in conjunction with conjugated polymer MEHPPV for harvesting solar energy. The energyconversion efficiency was obtained as 0.064% with a fill-factor of 0.52.

KEY WORDS: Hydrothermal synthesis; FeS2 nanoparticles; Optical characterization; Energy band gap

1. Introduction

The FeS2 in pyrite phase is an important material because ofits environmental compatibility and high stability towards photocorrosion[1]. It has attracted significant scientific interest and hasnumerous technological applications[2,3]. Owing to their largepotential capacities in application of devices, ironesulfur basedmaterials have been extensively studied by Kirkeminde et al.[4].The photo-sensing behavior mainly depends on the absorbanceand the direct band gap of the materials. The indirect band gapof FeS2 was measured as 0.95 eV by Ennaoui et al., which issuboptimal for single junction photovoltaic application[5]. Toimprove the band gap of pyrite FeS2, enormous efforts havebeen made. By controlling the environmental conditions of re-action, it is possible to synthesize high quality FeS2 nanoparticlewith desired property. Improvement in absorbance of FeS2 canbe done by tuning the nanomorphology. FeS2 nanoparticles withdifferent morphology have been fabricated by using a variety ofsynthetic methods[6]. Sun and Ceder studied and tried thetechnique to tune the band gap of FeS2 by controlling the par-ticle size[7]. As it had been reported so far, there are variousphases of FeS2, such as mackinawite (tetragonal), troilite

onding author. Prof., Ph.D.; Tel.: þ91 9475237259; Fax: þ918917; E-mail address: [email protected] (P. P. Ray).02/$e see front matter Copyright� 2014, The editorial office ofof Materials Science & Technology. Published by ElsevierAll rights reserved..doi.org/10.1016/j.jmst.2014.01.005

cite this article in press as: S. Middya, et al., Journal of Materials Scie

(hexagonal), pyrrhotite (monoclinic), smythite (hexagonal), py-rite (cubic), marcasite (orthorhombic) and greigite (cubic)[7].The solids consisting only of iron and sulfur are known to occurnaturally at lower temperature (below 200 �C). The structuralgrowth strongly depends upon the reaction temperature and thevapor pressure of the solvent. Wadia et al.[8] reported that ironpyrite (FeS2) is significantly attractive in both cost and avail-ability for the application of thin film technology. Like FeS2there are very few nano-semiconducting materials, which canmeet the large scale need, outside quantum confined systems[8].As the pyrite phase has more extensive stability in naturalenvironment in spite of its lower band gap, the use of this phaseis enormous. Unfortunately, the iron pyrite based solar energyharvesting devices have been plagued by performance problems.The science behind its underperformance is still not well un-derstood. After hard research work and a prolonged study it isidentified that the various phases of FeS2 produce surface de-fects near the surface of thin film and grain boundaries that limitthe open circuit voltage of the photovoltaic devices. Ennaouiet al. reported pyrite single crystal based photo electrochemicalcells, which show low open circuit voltage of 187 mV and fill-factor (FF) of 0.5[9]. The phase purity was attributed to low opencircuit voltage, which was reported by Thomas et al.[10]. Gantaet al.[11] successively synthesized superstrate type FeS2 and CdSink-based solar cell with efficiency of 0.03% and open circuitvoltage (Voc) of 565 mV. Several recent publications exhibitedthat successful and robust synthesis of pyrite nanocrystals andmany efforts have been directed toward exploring their opto-electronic applications[12e16]. Most recently (in the year 2012)

nce & Technology (2014), http://dx.doi.org/10.1016/j.jmst.2014.01.005

mailto:[email protected]

http://dx.doi.org/10.1016/j.jmst.2014.01.005

www.sciencedirect.com/science/journal/10050302

2 S. Middya et al.: J. Mater. Sci. Technol., 2014, -(-), 1e6

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% andVoc of 0.79 V[17], but the absorption and charge transportationhighly depends on the CdS quantum dot, rather FeS2. Biet al.[14] synthesized FeS2 NCs with improved stability in air andobserved a photo response in an ITO/FeS2 NC/Al device, but theresult is not upto the mark. Moreover, not surprisingly, norectification behavior was observed, as the pyrite formed ohmiccontacts at the ITO (indium tin oxides) and aluminum interfaces.Despite these recent works and renewed interest in pyrite FeS2over the past several years, no high performance device has beenmade yet based on this material. Further investigation on thefundamental properties of pyrite FeS2 and deployment in alter-native device architectures are required to explore the potentialof 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 vaporpressure of the solution, which can effectively control themorphology via controlling the growth rate. The optical ab-sorption of the synthesized material was studied by UVevisabsorption spectroscopy. Depending upon the morphologicalgrowth, energy absorption of as-synthesized iron pyrite wasnoticed as very low compared to other inorganic semiconductors.The optical band gap energy estimated from UVevis absorptiondata was significantly improved. This fact was in agreement withthe absorbing behavior of iron pyrite, for its modified architec-ture and epitaxial growth. The electrochemical band gap energywas calculated from oxidation (corresponding to valence band)and reduction (corresponding to conduction band) states with thehelp of cyclic voltammetry (CV). Thermal stability of the FeS2nanoparticle was studied with thermogravimetric analyzer(TGA). It is obvious that by controlling the growth ofmorphology with chemical surfactant, the band gap would suc-cessively tune up for application in high temperature semi-conducting electronic devices. Thus our synthesizedsemiconducting material with higher band gap and thermal sta-bility can be applied in photovoltaics at high temperature. It isnoteworthy that it has still remained as a challenging unexploredarena for the researchers. In the fore step we have fabricatedITO/PEDOT:PSS/MEH-PPV:FeS2/Al based hybrid solar cell andcharacterized the device to estimate different cell parameters.The polymer MEHPPV has a wide research application for itshigher absorption with band gap energy of 2.2 eV, as a semi-conducting donor polymer in fabrication of efficient thin filmhybrid solar cell. This was the early challenge to harvest solarenergy by mostly abundant iron-pyrite conjugated withMEHPPV. The subject still remains unexplored. The synthesizedFeS2 of higher band gap energy with corresponding energylevels demonstrates the successive charge transportation phe-nomena from MEHPPV donor to FeS2 acceptor and also ex-plains 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 sodiumsulfide (Na2S$9H2O), ammonium hydroxide (NH4OH), ethanol,

Please cite this article in press as: S. Middya, et al., Journal of Materials Scie

chloroform and polyethylene glycol (PEG-400) of AR gradewere 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 thesechemicals were used without further purification.

2.2. Synthesis of iron-pyrite nanoparticles

In this work FeS2 nanoparticles were synthesized by adoptinghydrothermal synthesis to curtail the manufacturing cost[18].20 ml 0.1 mol/L ferric chloride aqueous solution was prepared tomix with 20 ml 0.1 mol/L Na2S aqueous solution. The mixturewas stirred for 30 min with the help of magnetic stirrer. Bymaintaining the pH value of the solution within 6e7, NH4OHaqueous solution was added drop-wise to the mixture. A blackebrown precipitate was observed, and 10 ml PEG-400 was added.0.2 mg sulfur powder was mixed simultaneously with the solu-tion and was sonicated for 24 h. The desired mixture was thentransferred into a linear Teflon autoclave to be heated at 120 �Cfor 2 days. Then the nanoparticles were collected by washingwith ethanol and distilled water repeatedly by centrifugetechnique.

2.3. Device fabrication

Before device fabrication, the solutions of MEHPPV andsynthesized FeS2 nano-particle were prepared separately inchloroform with concentration of 10 mg/mL and 2 mg/mL,respectively. Solutions were mixed at appropriate weight ratiounder vigorous stirring by magnetic stirrer for 2 h to get thedesired mixture. As a buffer transparent layer, PEDOT:PSS wasspun on the patterned and pre-cleaned ITO substrate (cleanedwith acetone, ethanol and de-ionized water repeatedly underultra-sonic bath) at 1200 r/min for 2 min and then dried at100 �C. The active layers of blended solution of MEH-PPV:FeS2composite was prepared via spin coating at 2000 r/min for 2 minin open atmosphere with the help of SCU-2007 spin coating unit.Solvent evaporation has been done by heating the samples at100 �C for 10 min under vacuum oven. Thereafter, aluminumelectrode as back contact was deposited on to the active film withshadow mask by thermal evaporation technique with the help of12A4D HHV vacuum coating unit.

3. Characterization

The characterization of blackish FeS2 nanopowder was doneby recording powder X-ray diffraction (XRD) spectra with thehelp of Bruker D8-X-ray Diffractometer, Raman spectroscopy,field emission scanning electron microscopy (FE-SEM) andtransmission electron microscopy (TEM) of JEOL make. Toinvestigate the functional groups, which are responsible for ho-mogenous dispersion in chloroform medium, Fourier transforminfrared (FTIR) spectra were recorded with the help of FTIR-8400S Spectrophotometer of Shimadzu. The thermal stabilityof the sample was measured with DTG-60 thermogravimetricand differential thermal analyzer of Shimadzu. The sample washeated at a rate of 10 �C min�1 in a nitrogen atmosphere startingfrom 50 to 800 �C. The electrochemical measurements werecarried out using a Gamry reference 750 potentiostat in athree-electrode configuration. CV was performed using a con-ventional three-electrode system. The working electrode was a


Fig. 2 FE-SEM image of FeS2 nanoparticles.

S. Middya et al.: J. Mater. Sci. Technol., 2014, -(-), 1e6 3

photocatalyst powder-modified glassy carbon electrode (GCE)(3 mm diameter), the reference electrode was an Ag/AgCl (in3 mol/L NaCl) electrode, and the counter electrode was a plat-inum wire. The electrochemical band gap energy of the materialwas measured from CV data and the optical band gap energy wasevaluated from UVeVIS absorption data, recorded with the helpof 2401PC Shimadzu Spectrophotometer. To study the energyquenching of the composite, the photoluminescence spectra wererecorded with the help of Cary Eclipse Fluorescence Spectro-photometer from Varian. The current density vs voltage char-acteristic of the device was measured with Keithley 2400sourcemeter 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 fordiffraction were recorded as (111), (200), (210), (211), (220),(221), (311) and (222) at 2q ¼ 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 byJCPDS card no. 42-1340. Few extra peaks may be due to theattenuation and the presence of noise. Analysis of the XRDpattern using Scherrer’s broadening equation, estimates theparticle size[19]. From XRD spectrum by measuring the broad-ening of intensity at half maxima in radian and consideringwavelength (l) ¼ 0.154 nm (CuKa), the particle size of thematerial was evaluated with the auxiliary equation l/Bcosq as19 nm, where B represents the broadening constant and q is theBragg’s angle.Figs. 2 and 3 represent FE-SEM and TEM images of the as-

synthesized FeS2. These FE-SEM and TEM images exhibitedthat the size of the particles are in nano range (10e100 nm). Thecoagulations of the particles were observed from these electronmicroscopic imaging. The morphology of the particles is indis-tinguishable, which may be due to the coagulations of thenanoparticles. This is crudely related with the chain length of thecapping reagent and the solution vapor pressure.Fig. 4 represents FTIR spectroscopy of FeS2 nanoparticles.

This spectrum exhibited OeH stretching as peak at 3559 cm�1

and a broad peak centered around 3127 cm�1. The absorptionnear 1402 cm�1 corresponds to the CeH bending vibrationwhich came from the capping reagent (PEG-400). In addition,the band at 1124 cm�1 represented the asymmetric SeOstretching of the sulfate species, while the peak at 610 cm�1 wasthe consequence of the disulfide stretching (SeS)[20].

Fig. 1 XRD spectra of FeS2 nanoparticles.


To study the chemical bonds and symmetry of molecules thevibrational information has been gathered from Raman spec-troscopy. The active modes of Raman spectra consist of asymmetric mode (Ag), a doubly degenerate (Eg), and three triplydegenerate modes. Fig. 5 represents the Raman spectra of FeS2nanoparticle, recorded in the wave number range from 200 to1000 cm�1. In this spectra sharp peaks were observed at 339 and376 cm�1, which are the characteristic active modes for FeS2corresponding to the S2 libration (Eg) and in phase stretchingvibration of SeS dimer (Ag), respectively. In the Eg mode, the Satoms are displaced perpendicularly to the dimer axes. The peakat 497 cm�1 corresponds to the coupled libration and stretching(Tg) modes or their combination[21,22]. The above peaks exhibitthe pyrite cubic structure[23].Fig. 6 represents the thermal degradation of mass with

decomposition, which was recorded with increasing temperaturestarting from 50 to 800 �C by TGA. This TGA curve shows adrastic weight loss at around 50e250 �C. It may be caused bydehydration of the hydroxyls. Thereafter the degradation was notobserved till 600 �C, which indicates the thermal stability of thesample. Therefore, it is obvious from this graph that FeS2 isthermally stable up to 600 �C. After that the sample started to bedecomposed sharply. Finally the sample was decomposed to25% of its initial mass at temperature 800 �C. It may be due tothe dissociation of FeS2 into iron oxide. The important thing is to

Fig. 3 TEM image of FeS2 nanoparticles.


Fig. 4 FTIR spectra of FeS2 nanoparticles.

Fig. 5 Raman spectra of FeS2 nanoparticles.

Fig. 7 Tauc’s plot and band gap of FeS2 nanoparticles.

Fig. 8 Devis-Mott’s plot and band gap of FeS2 nanoparticles.


be noted that the high thermal constancy of FeS2, dignified thematerial for the application in high temperature environment(i.e., greater than room temperature).The UVevis absorption spectra of FeS2 nanoparticle,

dispersed in DMF solution is given in the inset of Fig. 7. Thesedata were analyzed with Tauc’s equation and considering theintercept of the sharp linear plot (ahn)2 vs incident photon en-ergy (hn) at incident energy axis. The direct optical band gap

Fig. 6 TGA curve of FeS2 nanoparticles.


energy of the nanomaterial at room temperature was measured as2.75 eV (Fig. 7). With these UVevis spectral data consideringDavis and Mott’s equation, the curve a (absorption coefficient)vs hn (incident photon energy) was plotted to estimate directoptical band gap energy of FeS2 nanomaterial (Fig. 8). From thisplot, the direct band gap energy of the nanomaterial was calcu-lated as 2.74 eV, which is not much different from the valueestimated by Tauc’s equation. The direct band gap of FeS2, re-ported so far is in the range from 0.7 to 2.6 eV[24]. In this study,

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


Fig. 10 Photoluminesence spectra of MEHPPV and MEHPPV:FeS2composite.

Fig. 11 Densityevoltage (JeV) characteristic curve of ITO/PEDOT:PSS/MEHPPV:FeS2/Al device.

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

S. Middya et al.: J. Mater. Sci. Technol., 2014, -(-), 1e6 5

the effective direct band gap at room temperature of the nano-material, as measured from Tauc’s and DaviseMott’s equation isappreciably high. It might be due to the epitaxial growth of thenanocrystal during hydrothermal synthesis[25e27], or due to theBursteineMoss effect[28,29]. According to BursteineMoss effect,depending upon the morphological growth of nanoparticles theabsorption edge is pushed to higher energies, as a result of allstates close to the conduction band being populated.Fig. 9 shows the cyclic voltammogram of dispersed FeS2

nanoparticles. The voltammogram shows an oxidation peak, i.e.,the ionization potential at approximately þ1.74 V and a reduc-tion peak, i.e., the electron affinity at about �0.99 V. In order toestimate the electrochemical band gap energy, the conductionand valence band energy (ECB and EVB) were calculated with thehelp of following equations

EVB ¼ �ðEox þ 4:14Þ eV

and

ECB ¼ �ðEred þ 4:14Þ eV

Table 1 Characteristics

Device Jsc (mA cm�2) Voc (V) FF

ITO/PEDOT:PSS/MEHPPV:FeS2/Al 0.130 0.72 0.52


as ECB ¼ �3.15 eVand EVB ¼ �5.88 eV, where Eox and Ered arethe onset potentials of the oxidation and reduction relative to anAg reference electrode, respectively. The value 4.14 eVrepresents the difference between the vacuum level potential ofthe normal hydrogen electrode and the potential of the Ag/AgNO3 electrode. Calculating the differenceDE ¼ ECB � EVB

[30], the energy band gap of FeS2 wasestimated as 2.73 eV.Fig. 10 represents the photoluminescence (PL) spectra of

MEHPPVand MEHPPV:FeS2 composite in chloroform medium,in thewavelength range from 450 to 750 nm. The figure shows thatfor the composite, PL excitation peak has been shifted from 558 to565 nm. The deviation of excitation peak of composite fromMEHPPV in chloroform medium indicates the energy quenchingwith red shift. The PL intensity is significantly reduced to 0.3 timesof the value of MEHPPV during formation of composite withFeS2. The static energy quenching of MEHPPV with incorpora-tion of FeS2 nanoparticle was observed distinctly in Fig. 9. Thus itis obvious that in MEHPPV:FeS2 composite, FeS2 nanoparticleacts as a semiconducting acceptor. The PL quenching is the evi-dence for exciton dissociation. When the photogenerated excitonsare dissociated, the probability for recombination should besignificantly reduced. This is the ultrafast electron transfer phe-nomena from donor to acceptor and it is expected to increase theexciton dissociation efficiency in photovoltaic devices[31,32].Fig. 11 represents the current densityevoltage (JeV) charac-

teristic of the device with structure ITO/PEDOT:PSS/MEHPPV:FeS2/Al. The effective diameter of each cell is 2 mm.The JeV characteristic of the device was recorded under theillumination of white light with incident power density of80 mW cm�2. From these characteristic curves the short circuitcurrent density (Jsc) and open circuit voltage (Voc) weremeasured as 0.13 mA cm�2 and 0.72 V, respectively. Themaximum power, maximum voltage, energy conversion effi-ciency, 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). Theseries and shunt resistances (Rs and Rsh) of the device, asmeasured from JeV curve are 53 U and 2.13 kU, respectively.From CV analysis of FeS2 by knowing the positions of energylevels, the exciton dissociations and charge transportationpath way from donor polymer (MEHPPV), with HOMO

data of the device

Vmax (V) Jmax (mA cm�2) Efficiency (%) Rs (U) Rsh (kU)

0.50 0.099 0.062 53 2.13



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 concernedmotivation and experimental effort consecutively. Thus newlyfound FeS2 with higher band gap energy can be a good candidatefor solar energy harvesting. To improve the efficiency of thedevice the thicknesses of different layers should be optimizedalong with material synthesis conditions.

5. Conclusion

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

AcknowledgmentsThis work was supported by University Grants Commission

(UGC), Govt. of India under project 39-508/2010 (SR). Theauthors acknowledge Madhusudan Nandy of Department ofChemistry, Jadavpur University and Priyanka Das of Departmentof Chemistry, West Bengal State University, Barasat for theirvaluable advice and enormous technical assistance.

REFERENCES

[1] I. Bedja, A. Hagfeldt, Adv. OptoElectron. 2011 (2011) 824927.[2] C. Wadia, Y. Wu, S. Gul, S. Volkman, J. Guo, A.P. Alivisatos,

Chem. Mater. 21 (2009) 2568e2570.[3] A. Ennaoui, S. Fiechter, H. Goslowsky, H. Tributsch, J. Electro-

chem. Soc. 132 (1985) 1579e1582.[4] A. Kirkeminde, B.A. Ruzicka, R. Wang, S. Puna, H. Zhao, S. Ren,

ACS Appl. Mater. Interfaces 4 (2012) 1174e1177.[5] A. Ennaoui, S. Fiechter, C. Pettenkofer, N. Alonso-Vante, K. Buker,

M. Bronold, C. Hopfner, H. Tributsch, Sol. Energy Mater. Sol. Cells29 (1993) 289e370.


[6] S. Disale, S. Garje, Adv. Sci. Lett. 3 (2010) 80e86.[7] R. Sun, G. Ceder, Phys. Rev. B 84 (2011) 245211.[8] C. Wadia, A.P. Alivisatos, D.M. Kammen, Environ. Sci. Technol.

43 (2009) 2072e2077.[9] A. Ennaoui, S. Fiechter, W. Jaegermann, H. Tributsch, J. Electro-

chem. Soc. 133 (1986) 97e106.[10] B. Thomas, K. Diesner, T. Cibik, K. Ellmer, Solid State Phenom.

51e52 (1996) 301e306.[11] L.K. Ganta, T.P. Dhakal, S. Rajendran, C.R. Westgate, MRS Proc.

1447 (2012). http://dx.doi.org/10.1557/opl.2012.1064.[12] 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) 405207.[13] J. Puthussery, S. Seefeld, N. Berry, M. Gibbs, M. Law, J. Am.

Chem. Soc. 133 (2011) 716e719.[14] Y. Bi, Y.B. Yuan, C.L. Exstrom, S.A. Darveau, J.S. Huang, Nano

Lett. 11 (2011) 4953e4957.[15] D.Y. Wang, Y.T. Jiang, C.C. Lin, S.S. Li, Y.T. Wang, C.C. Chen,

C.W. Chen, Adv. Mater. 24 (2012) 3415e3420.[16] L.P. Yu, S. Lany, R. Kykyneshi, V. Jieratum, R. Ravichandran,

B. Pelatt, E. Altschul, H.A.S. Platt, J.F. Wager, D.A. Keszler,A. Zunger, Adv. Energy Mater. 1 (2011) 748e753.

[17] A.Kirkeminde,R. Scott, S. Ren,Nanoscale 4 (24) (2012) 7649e7654.[18] X. Feng, X. He, W. Pu, C. Jiang, C. Wan, Ionics 13 (2007) 375e377.[19] P. Scherrer, Math.-Phys. Kl. 1918 (1918) 98e100.[20] J.M. Philias, B. Marsan, Electrochem. Acta 44 (1999) 2351e2363.[21] B. Yuan, W. Luan, S. Tu, Dalton Trans. 41 (2012) 772e776.[22] M.Y.C. Teo, S.A. Kulinich, O.A. Plaksin, A.L. Zhu, J. Phys. Chem.

A. 114 (2010) 4173e4180.[23] X. Qiu, M. Liu, T. Hayashi, M. Miyauchi, K. Hashimoto, Chem.

Commun. 49 (2013) 1232e1234.[24] J.P. Pemsler, R.K.F. Lam, J.K. Litchfield, S. Dallek, B.F. Larrick,

B.C. Beard, J. Electrochem. Soc. 137 (1990) 1e8.[25] P. Masset, J.Y. Poinso, J.C. Poignet, J. Thermal Anal. Calorim. 83

(2006) 457e462.[26] I.J. Ferret, D.M. Nevskaia, C. de las Heras, C. Sanchez, Solid State

Commun. 74 (1990) 913e916.[27] G. Smestad, A. da Silva, H. Tributsch, S. Fiechter, M. Kunst,

N. Mezziani, M. Birkholz, Sol. Energy Mat. 18 (1989) 299e313.[28] C. Liu, C. Pettenkofer, H. Tributsch, Surf. Sci. 204 (1988) 537e554.[29] K. Sato, Prog. Cryst. Growth Charact. 11 (1985) 109e154.[30] Y. Abdollahi, A.H. Abdullah, Z. Zainal, N.A. Yusof, Int. J. Basic

Appl. Sci. 11 (2011) 118104.[31] P. Chakraborty, G. Datta, K. Ghatak, Phys. Scripta 68 (2003)

368e377.[32] E. Kucur, J. Riegler, G.A. Urban, T. Nann, J. Chem. Phys. 119

(2003) 2333e2337.


http://refhub.elsevier.com/S1005-0302(14)00011-5/sref1



























http://dx.doi.org/10.1016/j.jmst.2014.01.005
























































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

Documents

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