AACVD experiments at all temperatures resulted in the deposition of a reddish black indium selenide material; however, the best deposition was achieved at 4501C.. Quite sharp peaks in th
Trang 1Deposition of binary, ternary and quaternary metal selenide thin films
from diisopropyldiselenophosphinato-metal precursors
Sumera Mahbooba,b, Sajid N Malika,c, Nazre Haiderd, C Q Nguyene,
Mohammad A Malika, Paul O ’Briena,n
a
Schools of Chemistry and Materials, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
b
Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
c
School of Chemical & Materials Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan
d National Engineering and Scientific Commission, Islamabad 44000, Pakistan
e Faculty of Chemistry, University of Science, Vietnam National University, Hochiminh City, Vietnam
a r t i c l e i n f o
Article history:
Received 3 October 2013
Received in revised form
20 January 2014
Accepted 23 January 2014
Communicated by R Fornari
Available online 11 February 2014
Keywords:
A1 Thin films
B1 Chalcopyrite
CIS
AACVD
CIGS
a b s t r a c t
The tetragonal chalcopyrite phases CuInSe2, CuGaSe2and CuIn0.7Ga0.3Se2have been deposited onto the glass substates by Aerosol Assisted Chemical Vapour Deposition (AACVD) from a mixture of [Mx(iPr2PSe2)y] complexes (M¼In, Ga, Cu) at temperatures between 300 1C and 500 1C The thin films were characterized
by powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) The bulk compositional properties have been studied by energy dispersive X-ray (EDX) analysis SEM and AFM studies demonstrate a significant variation in morphology of the deposited materials at different deposition temperatures
& 2014 Elsevier B.V All rights reserved
1 Introduction
Metal chalcogenide semiconductor thin films have attracted
significant research attention during the past few decades because
of their exciting photoelectrical characteristics Copper selenide,
a member of II–VI family of semiconductors, has found diverse
applications in the photothermal therapy of cancer [1] and in
electronic and optoelectronic devices like solar cells [2], optical
filters[3], thermoelectric converters[4], and super ionic
conduc-tors[5] Indium selenide, a III–VI semiconductor, consists of Se–In–
In–Se sheets which are two dimensionally arranged to give
a hexagonal crystalline structure By virtue of such a layered structure,
indium selenide exhibits highly anisotropic optical and electronic
properties[6] Indium selenide is a potentially suitable material for
solar photovoltaics and electrochemical devices like photodetectors[7],
ion batteries[8], and solid solution electrodes[9,10]
Similarly, copper indium diselenide (CIS) and related copper
chalcopyrite semiconductors are among the most important
photo-absorbing materials for polycrystalline thinfilm solar photovoltaics
These direct band gap materials offer high absorption coefficients
(4105cm1), greater photo-irradiation stability and very little/no toxicity [11] CuInSe2 has a direct band gap of 1.04 eV which is considerably lower than the optimal value for terrestrial solar cell applications whereas its gallium analogue copper gallium diselenide (CuGaSe2) has a band gap of 1.68 eV [12] Copper indium gallium diselenide (CIGS) may be considered as a pseudobinary alloy of ternary CuInSe2and CuGaSe2materials, in which indium (In) atoms in the CIS superlattice are gradually replaced by the gallium (Ga) atoms This system may be generally represented as CuIn1xGaxSe2 and offers flexible band gap engineering of the material from 1.04 eV to 1.68 eV
by gradual substitution of Ga for In atoms Recently, Jackson et al., have reported 20.1% and 20.3% efficiencies for CIGS thin-film solar cells[13]
A number of stoichiometric compositions (CuSe, Cu2Se, CuSe2,
Cu3Se2, Cu5Se4, Cu7Se4 etc.) and non-stoichiometric composition (Cu2xSe), have been reported for copper selenide [14–18] The copper selenide thinfilms have been deposited by using a variety
of techniques like vacuum evaporation[19], solvothermal method [20], melting of elemental copper and selenium[21], electrodepo-sition[22], D.C magnetron sputtering[23],solution phase growth [24], chemical bath deposition[25]and chemical vapour deposi-tion (CVD)[26] Similarly, the In2Se3thinfilms have been grown
by a number of techniques like elemental evaporation [27], spray pyrolysis [28], sol–gel synthesis [29], electrodeposition [30], molecular beam epitaxy [31] and MOCVD including LPCVD
Contents lists available atScienceDirect
journal homepage:www.elsevier.com/locate/jcrysgro Journal of Crystal Growth
http://dx.doi.org/10.1016/j.jcrysgro.2014.01.049
0022-0248 & 2014 Elsevier B.V All rights reserved.
n Corresponding author Tel./fax: þ44 161 2751411.
E-mail address: paul.obrien@manchester.ac.uk (P O’Brien).
Trang 2and AACVD[32,33] The absorber layer in CIGS solar cells and the
modules with record efficiency has been deposited by the
co-evaporation process [34] Moreover other techniques have also
been used for deposition of CuInSe2and related copper
chalcopyr-ite thinfilms These techniques include molecular beam epitaxy
(MBE)[35], chemical vapor deposition (CVD)[36], chemical bath
deposition (CBD) [37], sputtering [38], successive ionic layer
absorption and reaction (SILAR) method [39], electrodeposition
[40], spray deposition [41], pulsed laser deposition [42] and
microwave irradiation[43]
Generally, the deposition of a metal selenide thinfilms is
encoun-tered with problems of obtaining a polyphasic mixture or the
materials with bad orientation, unless expensive deposition
techni-ques are employed It is still a challenge to precisely control the grain
size, shape and the stoichiometric composition of deposited material,
especially while scaling up the process CVD has a remarkable
potential for scaling up the technology as has already been
demon-strated in the process of deposition of self cleaning TiO2coatings onto
soda lime glass[44] The dilemma offinding chemical precursors with
optimal volatility, however, limits the usefulness of the conventional
CVD technique AACVD circumvents this difficulty and offers relatively
better control over the stoichiometric composition of the deposited
materials Marchand et al have recently reviewed diverse applications
and advantages of the AACVD process in materials fabrication[45]
Therefore, our previous efforts include precursor design and the
deposition of semiconductor materials by a variety of techniques,
especially AACVD
We have successfully used a single source precursor approach
for the deposition of good quality thinfilms of metal
chalcogen-ides Previously, we have reported the deposition of Cu2 xSe thin
films by LP-MOCVD and AACVD using carbamato-compound Cu
[E2CNMenHex]2 as a single source precursor [46] Our previous
research efforts also include deposition of In2Se3and Ga2Se3thin
films from [In{Se2CN(Me)Hex}3 [47], In[(SePiPr2)2N]2Cl [48],
[Me2In(Se2PiPr2)2N], [Et2In(Se2PiPr2)2N] and [Me2Ga(SePiPr2)2N]
precursors[49] We have also reported the deposition of CuInSe2,
CuInS2, and CuGaS2thinfilms using Cu(II) and In(III) complexes of
methyl-n-hexyl-diselenocarbamate as dual-source precursors by
LP-CVD and AACVD[50] Similarly, we have also used Cu(II) and
In(III) complexes of iminobis(diisopropylphosphineselenide), for
the deposition of CuInSe2thinfilms by AACVD[51] Our previous
efforts also include a facile and reproducible synthesis of air and
moisture stable [HNEt3][iPr2PSe2] ligand and its complexes with a
variety of metals[52] Herein, we report the deposition of phase
pure polycrystalline thinfilms of In2Se3, Cu2 xSe, CuInSe2, CuGaSe2
and CuIn0.7Ga0.3Se2 from diisopropyldiselenophosphinato-metal
complexes as precursors
2 Experimental
Chlorodiisopropylphosphine, triethylsilane, triethylamine, Se
pow-der 100 mesh, indium(III) chloride, gallium(III) chloride, copper(II)
chloride, copper(I) chloride and hexane were obtained from
Sigma-Aldrich and used as received Synthesis of ligand salt [HNEt3][iPr2PSe2]
and its complexes with indium(III), gallium(III) and copper(I) was
carried out in accordance with the previously reported procedures
[52] Solvents toluene and methanol were dried through distillation
over sodium/benzophenone and calcium hydride prior to use
All synthetic manipulations were carried out under nitrogen
atmosphere by employing the Schlenk line techniques A glove box
filled with nitrogen was used to handle pyrophoric and air
sensitive chemicals (e.g GaCl3) The glassware was flame dried
along with evacuation followed by purging with dry nitrogen to
remove moisture before each experiment 1H NMR spectra were
recorded on Bruker AC300 FT-NMR spectrometer and a Kratos
Concept 1S instrument was used to record mass spectra Elemental analyses were performed on CHN Analyzer LECO model CHNS-932 Melting points were recorded using a Stuart melting point apparatus and are uncorrected
2.1 Deposition of thinfilms by AACVD The substrates used for the deposition of thinfilms were glass slides (1 3 cm) which were thoroughly cleaned to remove any possible contamination All AACVD experiments for the deposition
of thin films were performed using a self designed AACVD Kit described elsewhere[53] In a typical experiment, 150 mg of the precursor (or a precursor mixture in the desired ratio in case of ternary and quaternary thinfilms) in 15 mL toluene was added in
a two-necked 100 mL round-bottom flask with a gas inlet that allowed the carrier gas (argon) to pass through the solution and aid transport of the aerosols This flask was connected to the reactor tube by a piece of reinforced tubing A Platonflow gauge was used to control argonflow rate at 130 mL/min
Six glass substrates were positioned in the reactor tube which was in turn placed in a Carbolite furnace A round-bottomflask containing the precursor solution was placed in a water bath just above the piezoelectric modulator of a PIFCO ultrasonic humidifier Carrier gas transferred thus generated aerosols to the hot zone of the reactor Both the solvent and the precursor underwent thermolysis at the hot substrate surface where the deposition of film took place as a result of thermally induced reaction Deposi-tion was carried out at different temperatures i.e 3001C, 350 1C,
4001C, 450 1C and 500 1C at a constant argon flow rate on substrates for 1.5 h
A Bruker D8 AXE diffractometer (Cu-Kα) was used to record p-XRD patterns of the thinfilms The samples were scanned from
20 degrees to 80 degrees, in a step size of 0.05 Edwards E-306A coating system was used for carbon coating of the thinfilms Film morphology was investigated by using a Philips XL 30 FEGSEM and film composition was studied by EDX analysis using a DX4 instrument AFM images were recorded on Veeco-CP II microscope
3 Results and discussion The ligand salt [HNEt3][iPr2PSe2] was synthesized using litera-ture procedure except that a 20% excess of triethylamine was used
in the reaction Excess triethylamine ensures the availability of [HNEt3]þin the reaction medium and suppresses the formation of bis(diisopropylselenophosphinyl)-selenide (R2PSe)2Se thus signi fi-cantly improving the yield of reaction Reaction of the ligand salt [HNEt3][iPr2PSe2] with metal halides (CuCl, InCl3 and GaCl3) at room temperature yielded air and moisture stable complexes with
a fair purity and in a good yield These complexes were character-ized and subsequently used as precursors for the deposition of metal chalcogenide thinfilms
3.1 Thermogravimetric analyses Thermogravimetric analyses (TGA) were carried out to assess the thermal decomposition behaviour of the complexes TGA curves of the copper, indium and gallium complexes are shown
inFig 1 The TGA curve of [Cu4(iPr2PSe2)4] shows that the copper precursor decomposes cleanly in one step at around 3401C with residue (43.8%) in close accordance with the CuSe percentage (42.1%) in the precursor The TGA curve for [In(iPr2PSe2)3] shows that the complex decomposes in 2 steps; at 3501C (62% weight loss) and at 4751C (5% weight loss) Above 480 1C the residue is 23.5%, which is in a good agreement with the calculated value for
InSe (24.8%) TGA analysis of [Ga(iPrPSe )] demonstrates that
Trang 3decomposition of this complex is not clean and occurs in two
steps Therefore, this complex may not be a suitable precursor for
deposition of Ga2Se3material, especially at a temperature below
5001C This inference was later confirmed experimentally as
AACVD experiments using this precursor alone gave no
appreci-able deposition of Ga2Se3onto the substrates up to 5001C
3.2 Deposition of copper selenide thinfilms
Copper selenide thinfilms were deposited from [Cu4(iPr2PSe2)4]
by AACVD at temperatures ranging from 3001C to 500 1C
At 3001C, no deposition was observed on the substrates However,
experiments at 3501C and higher temperatures gave the uniform
deposition of a black, shiny and well adhered material The
powder X-ray diffraction (p-XRD) patterns of thinfilms grown at
3501C, 400 1C, 450 1C and 500 1C are shown inFig 2A Analysis of
the p-XRD patterns revealed that the berzelianite phase of
Cu2xSe (ICDD pattern 00-006-680) was deposited at all
tempera-tures No peaks corresponding to other phases of copper selenide
were observed in the diffraction pattern Relatively narrow and
sharper peaks were observed for thinfilms deposited at 450 1C
and 5001C This indicates a larger grain size and better
crystal-linity of the Cu2 xSe material deposited at higher temperatures
The surface morphology of as deposited films was studied
using scanning electron microscopy Representative SEM images of
Cu2xSe films deposited at various temperatures are shown in
Fig 2B It was evident that the shape of the deposited grains varies
significantly with the deposition temperature Randomly
distrib-uted globular grains are formed at 3501C whereas deposition at
higher temperature yields a granular and predominantly triangular
morphology At 5001C, large grains with multiple triangular
faceting were clearly visible EDX analysis shows deviation from
normal stoichiometric ratio of 2:1 for copper and selenium
Materials obtained at 3501C and 400 1C temperatures were
slightly Cu deficient having Cu to Se ratio of 1.92:1 while those
obtained at 4501C and 500 1C were even more Cu deficient having
1.85:1 stoichiometry A summary of EDX results of the thinfilms
deposited at different temperatures is given inTable 1
3.3 Deposition of indium selenide thinfilms
[In(iPr2PSe2)3] was used as a single source precursor (SSP) for
the deposition of In2Se3thinfilms at temperatures ranging from
3001C to 500 1C AACVD experiments at all temperatures resulted
in the deposition of a reddish black indium selenide material; however, the best deposition was achieved at 4501C The films deposited at this temperature were well adhered to the substrate and successfully passed the scotch-tape test Crystallographic phase of the deposited material was determined by using p-XRD technique Fig 3A shows p-XRD patterns of the thin films deposited at different temperatures The p-XRD patterns revealed that the material deposited at all the temperatures corresponds to γ-phase of In2Se3(standard ICDD pattern 00-040-1407) which was preferentially oriented along (1 1 0) plane The crystallinity of the
In2Se3 material was reflected by sharpness of the XRD peaks Furthermore, appearance of no additional peaks indicates that material is significantly pure and monophasic as no other phases
of indium selenide were observed
SEM images of the as deposited thin films (Fig 3B) were obtained to study the surface morphology and microstructure of the deposited material The SEM images showed uniform cover-age of the substrates with highly crystalline grains deposited Different morphologies of the grains were obtained at different deposition temperatures The deposition at 3501C and 400 1C yielded flake like structures whereas cylindrical grains with approximate dimensions of 1.27–1.36 μm 1.79–1.95 μm were deposited at 4501C The deposition experiments at 500 1C resulted in randomly oriented plates A homogeneous distribu-tion of grains on the surface was clearly evident in all thefilms The stoichiometric composition of the material was determined
by EDX analysis which showed that the material obtained is slightly Se rich, the ratio of indium to selenium being 2.05:3.5 Furthermore, no appreciable difference in the stoichiometric composition of the individual grains was observed Optical band gap of the films deposited at 450 1C was determined by extra-polating the straight line part of the (αthυ)2
vs hυ curve to the
hυ axis, where (αthυ)2¼0, and was found to be 1.82 eV The bandgap values of different thinfilms deposited at 450 1C are given inTable 2
3.4 Deposition of CuInSe2thinfilms CuInSe2 thinfilms were deposited from 1:4 M equivalents of [Cu4(iPr2PSe2)4] and [In(iPr2PSe2)3] precursors A very poor cover-age of thefilm was obtained at 300 1C However, the deposition experiments at 3501C to 450 1C yielded weakly adhered, black and shinyfilms which did not qualify the scotch tape test
The p-XRD patterns of the thinfilms were recorded to deter-mine the crystallographic phase of the material p-XRD patterns (Fig 4A) demonstrated that tetragonal phase of CuInSe2(standard ICDD pattern 01-075-0107) was deposited at all temperatures
In all the cases, the deposited material had a preferred orientation along (1 1 2) plane which is typical for ternary copper chalcopyrite compounds deposited by CVD Quite sharp peaks in the p-XRD pattern especially at a higher temperature reflected an improved crystallinity of the material, whereas a pure and monophasic nature of deposited material was demonstrated by the absence
of any additional peaks due to possible binary phases of copper and/or indium selenide
The microstructure of the thin films was studied with the help of scanning electron microscopy The SEM images (Fig 4B) show that the film deposited at 300 1C consists of clusters
of an undefined shape randomly distributed onto the substrate However, at 3501C to 450 1C, the films exhibited good coverage with material having predominantly rice like morphology with uniform grain size and well defined grain boundaries especially
at 4501C EDX analysis showed that the ratio of Cu:In:Se was close to 1:1:2 for CuInSe2 stoichiometry in all the films About 3% of phosphorus contamination was found on the films grown at a lower temperature (3001C, and 350 1C); however
Fig 1 TGA curves showing decomposition behavior of (a) [Cu 4 ( i Pr 2 PSe 2 ) 4 ],
(b) [Ga( i Pr 2 PSe 2 ) 3 ] and (c) [In( i Pr 2 PSe 2 ) 3 ] precursors.
Trang 4no such contamination was found on thefilms deposited at higher
temperatures
AFM was also used to study surface morphology of the CuInSe2
films AFM images of CuInSe2thin films deposited at 400 1C are
shown in Fig 4C The images revealed that deposited material
consists of uniform sized granules which are homogeneously
distributed onto the surface of glass substrates as agglomerates
Root mean square roughness of the thinfilm surface was
calcu-lated by acquiring a number of scans from different areas of the
film and found to be 130.8 nm The optical band gap of the films
deposited at 4501C was found to be 1.13 eV whereas the
reported band gap energies of CuInSe2 are 1.05 eV, 1.13 eV and
1.2 eV[54]
3.5 Deposition of CuGaSe2thinfilms [Cu4(iPr2PSe2)4] and [Ga(iPr2PSe2)3] precursors were used in a 1:4 M equivalents respectively to carry out the deposition of CuGaSe2 thin films at the temperatures ranging from 350 1C to
5001C Poor films were obtained at 350 1C which gave a poor diffraction in p-XRD Greenish black films were obtained at
400–450 1C deposition temperature whilst the film deposited
at 5001C showed a very fine black powder layer on the surface
of substrates which may be attributed to an excess of the same deposited material p-XRD patterns of as-deposited thinfilms of CuGaSe2 are shown in Fig 5A The films deposited at lower temperature did not give a good diffraction pattern due to low
Fig 2 (A) p-XRD patterns of as deposited Cu 2x Se thin films from [Cu 4 ( i Pr 2 PSe 2 ) 4 ] precursor at temperatures (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C Vertical lines below show the standard ICDD pattern 00-006-680 for berzelianite phase of Cu 2x Se (B) SEM images of as deposited thin films of Cu 2x Se at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C.
Trang 5crystallinity of the material However, broader peaks were
obtained for the thin film deposited at 400 1C These p-XRD
patterns demonstrate that the material is not very crystalline
and consists of small grains No extra peaks were observed in
the diffraction pattern recorded at 4001C, but some extra peaks
assignable to copper selenide were found in the diffraction pattern
of the film deposited at 450 1C At 500 1C, a sharp diffraction
pattern was obtained which showed deposition of tetragonal
phase of chalcopyrite CuGaSe2(ICDD 00-035-1100)
The surface morphology of thefilms was studied with the help
of scanning electron microscopy SEM images of the thin films
deposited at different temperatures are shown inFig 5B It was
observed that morphology of CuGaSe2 thin films was strongly
influenced by the deposition temperature As expected, films
deposited at 3501C showed deposition of very small globules
which were not crystalline enough to give a good diffraction
pattern SEM images of the thin films deposited at 400 1C and
4501C reveal the formation of nano wires These wires are less
dense and randomly distributed onto the surface of substrate at
4001C while deposition at 450 1C yielded the densely covered and
well adhered films The deposition at 500 1C resulted in the
formation of randomly oriented globular structures of uniform
size EDX analyses showed a stoichiometric ratio closer to the
expected 1:1:2 ratio for copper, gallium and selenium However,
a slight excess of Se was found in the films deposited at lower
temperatures Phosphorus contamination was observed in the thin
films deposited below 450 1C, however no considerable phosphorous
contamination was observed in thefilm deposited at 500 1C
Surface profile of the films was further examined with the help
of atomic force microscopy (AFM) Two-dimensional and three
dimensional AFM images of CuGaSe2thinfilm deposited at 500 1C
are shown inFig 5C, which shows a root mean square roughness
of 41.39 nm for the surface of as-depositedfilm An optical band
gap of thefilm deposited at 450 1C was measured by the direct
band gap method and found to be about 1.67 eV
3.6 Deposition of CuIn0.7Ga0.3Se2thinfilms
Thinfilms of CIGS were deposited onto the glass substrates by
using different molar equivalents of [Cu4(iPr2PSe2)4, [In(iPr2PSe2)3]
and [Ga(iPr2PSe2)3] to obtain films of varying stoichiometric
combinations The deposition experiments were carried out using
1:1:1 M, 1:2:2 M and 1:2:4 M ratios of copper, indium and gallium precursor, respectively, at temperatures ranging from 3501C to
5001C For all molar ratios, black shiny films were obtained Previously, we have reported the colloidal synthesis of nano-particles from these precursors[55] It was demonstrated that by varying the molar ratios of copper, indium and gallium precursors, different stoichiometric compositions of CuIn1 xGaxSe2 nanopar-ticles could be obtained However, in case of the thinfilms, p-XRD patterns of the thinfilms deposited from different molar combina-tions of precursors revealed that more than one phase of material was deposited in the case of 1:1:1 M and 1:2:4 M ratios of Cu,
In and Ga precursors, respectively Besides CIGS, CuGaSe2, Cu2xSe and CuInSe2 were present as impurities Only in the case of deposition involving 1:2:2 M ratios of copper, indium and gallium precursors, respectively, a phase pure material with no traceable impurities was deposited The p-XRD patterns (Fig 6A) obtained in this case were assignable to a tetragonal CuIn0.7G0.3Se2 crystal-lographic phase (ICDD pattern 00-035-1102) with preferred orien-tation along (1 1 2) plane No other stoichiometric compositions of CIGS could be obtained The well defined and sharp diffraction peaks indicated that the material was sufficiently crystalline and purity of as-deposited chalcopyrite material was evident from the absence of any additional diffraction peaks of possible binary phases or impurities
The SEM images, as shown inFig 6B, revealed that thefilms were uniformly covered with material having well defined shapes of grains It was further observed that the shapes of grains are influenced by the deposition temperature Randomly oriented grains of indefinite geometry were deposited at 350 1C, while evenly distributed, uniform sized flakes like crystallites were deposited at 4001C to 500 1C A high magnification view
of the film deposited at 450 1C is given inFig 6B(e) EDX data
of CIGS across the entire film revealed a uniform composition that was fairly compatible with the stoichiometric ratio expected for CuIn0.7Ga0.3Se2
Surface roughness of thefilms is decreased as larger and more uniform grains are deposited at higher deposition temperatures The same is observed from AFM analysis (Fig 6C), which revealed that the root mean square roughness of CIGS deposited at 4001C was 55.46 nm while CIGS deposited at 4501C had a root mean square roughness of 44.50 nm An optical band gap of CuIn0.7
-Ga Se material deposited at 4501C from 1:2:2 M equivalents of
Table 1
EDX analyses results of thin films deposited at different temperatures.
Trang 6copper, indium and gallium precursors, respectively, was found to
be 1.46 eV The values of band gap energies reported in literature
for CIGS vary from 1.04 eV to 1.68 eV depending upon the
composition
SEM images of the thinfilms deposited from 1:1:1 M equivalents
of copper, indium and gallium precursors revealed the presence of additional phases, especially Cu2xSe and CuInSe2along with grains
of CIGS material Deviation from targeted stoichiometry was observed in all these experiments Attempts to deposit gallium rich CIGS thinfilms by increasing the molar ratio of gallium precursor (by using 1:2:4 M ratio for copper, indium and gallium precursors) proved unsuccessful In this case, additional phases of CuGaSe2and
Ga2Se3were obtained instead These results fully conform to those deduced from aforementioned p-XRD analysis of thefilms
4 Conclusions The deposition of In2Se3, Cu2xSe, CuInSe2, CuGaSe2 and CuIn-GaSe (CIGS) thinfilms from diisopropyldiselenophos-phinato-metal
Fig 3 (A) p-XRD patterns of as deposited In 2 Se 3 thin films from In( i
Pr 2 PSe 2 ) 3 ] precursor at temperatures (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C Vertical lines below show the standard ICDD pattern 00-040-1407 for γ-In 2 Se 3 (B) SEM images of as deposited In 2 Se 3 thin films at (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C.
Table 2
Bandgap values of different thin films deposited at 450 1C.
Thin film material
(deposited at 450 1C)
Bandgap (eV) (calculated value)
Bandgap (eV) (literature value)
Reference
CuIn 0.7 Ga 0.3 Se 2 1.46 1.05 to 1.65 n [56]
n The band gap of CuIn 1x Ga x Se 2 thin films varies from 1.05 to 1.65 eV with
increasing Ga.
Trang 7complexes by AACVD has been demonstrated in this study [In
(iPr2PSe2)3] and [Cu4(iPr2P2Se2)4] complexes deposited
monopha-sicγ-In2Se3and Cu2xSefilms, respectively Both of the ternary
materials (CuInSe, CuGaSe ) were deposited in the tetragonal
phase and they showed a preferred orientation along (1 1 2) plane
in their p-XRD Different molar ratio combinations of the copper, indium and gallium precursors for the deposition of CIGS resulted
in the mixed phase material except in a molar ratio of 1:2:2 which
Fig 4 (A) p-XRD patterns of as deposited CuInSe 2 thin films from 1:4 M ratios of copper and indium precursor at temperatures (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C indexed with standard ICDD pattern 01-075-0107 (B) SEM images of as deposited thin films of CuInSe 2 at (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C (C) 2D and 3D AFM images showing surface roughness of as deposited CuInSe 2 thin film deposited at 450 1C.
Trang 8Fig 5 (A) p-XRD pattern of CuGaSe 2 thin films deposited from 1:4 M ratios of Cu and Ga precursors at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C Vertical lines below show standard ICDD pattern 00-035-1100 for CuGaSe 2 (B) p-XRD pattern of as deposited CuGaSe 2 thin films at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C from 1:4 M ratios of Cu and Ga precursors (C) 2D and 3D AFM images of as grown CuGaSe 2 thin films from 1:4 equivalent of [Cu 4 ( i
Pr 2 P 2 Se 2 ) 4 ] and [Ga( i
Pr 2 PSe 2 ) 3 ] precursors
at 450 1C.
Trang 9Fig 6 (A) p-XRD pattern of as deposited CuIn 0.7 Ga 0.3 Se 2 thin films at (a) 300 1C, (b) 350 1C, (c) 400 1C, (d) 450 1C and (e) 500 1C from 1:2:2 M equivalents of [Cu 4 ( i Pr 2 P 2 Se 2 ) 4 ], [In( i Pr 2 PSe 2 ) 3 ] and [Ga( i Pr 2 PSe 2 ) 3 ], respectively, indexed with standard ICDD pattern 00-035-1102 (B) SEM images of as deposited CuIn 0.7 Ga 0.3 Se 2 thin films at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C (e) Higher magnification image of thin film deposited at 450 1C showing individual CIGS grains (C) (a) 2D, (b) 3D AFM images of as deposited CuIn 0.7 Ga 0.3 Se 2 at 450 1C with Root mean square roughness 44.50 nm, (c) 3D AFM image of CuIn 0.7 Ga 0.3 Se 2 thin film deposited at 400 1C (d) 3D AFM image of nano indent type microstructures found at film surface.
produced phase pure CuIn0.7G0.3Se2 Significant differences were
noticed in the morphology of the thin films with the
deposit-ion temperature in all cases Future work will involve the use of
these complexes with corresponding thiocarbamato complexes to
deposit a more versatile multinary material Cu(In1xGax)(Se1ySy)2.
Acknowledgements
S N Malik and S Mehboob would like to acknowledge the
DESTO, Government of Pakistan forfinancial support
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