Synthesis and structure of [(Ph3P)2Cu(μ-SeCH2Ph)2In(SeCH2Ph)2] as a single-source precursor for the preparation of CuInSe2 nano-materials

Article abstract of DOI:10.1039/c9ra03429c

The reaction of freshly prepared Na[In(SeCH₂C₆H₅)₄] with the mixture of CuCl and triphenylphosphine in methanol yielded [(PPh₃)₂CuIn(SeCH₂C₆H₅)₄]

Full text of DOI:10.1039/c9ra03429c

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Synthesis and structure of [(Ph3P)2Cu(m-
SeCH2Ph)2In(SeCH2Ph)2] as a single-source
precursor for the preparation of CuInSe2 nano-
materials†
Cite this: RSC Adv., 2019, 9, 18302
a
Manoj K. Pal,a Sandip Dey,
Suman Neogyb and Mukesh Kumarc
*
The reaction of freshly prepared Na[In(SeCH2C6H5)4] with the mixture of CuCl and triphenylphosphine in
methanol yielded [(PPh3)2CuIn(SeCH2C6H5)4]. The X-ray structure of the complex revealed the monomeric
form of [(Ph3P)2Cu(m-SeCH2Ph)2In(SeCH2Ph)2] consisting of tetrahedral Cu(I) and In(III) centers, bridged by
two benzyl selenolate ligands. The complex on pyrolysis in a furnace or in oleylamine/HDA yielded
tetragonal CuInSe2. The morphology and composition of nanostructures were investigated by pXRD, SEM,
TEM and EDX analysis. The band gap of the CuInSe2 nanostructures, obtained from pyrolysis in HDA and
OA has been deduced from DRS as 1.85 and 1.86 eV, respectively.
Received 7th May 2019
Accepted 27th May 2019
DOI: 10.1039/c9ra03429c
rsc.li/rsc-advances
CIS nanoparticles have been prepared by a solution-based
one step process using three different sources of Cu, In and
Se with capping agents to control the size, shape and
Introduction
The ternary chalcogenides CuME2 (M ¼ Ga, In; E ¼ S, Se) have
been established as the key components in several optoelectronic
applications such as photovoltaics (PV), light-emitting diodes
and photocatalytic H2 generations depending on their composi-
tions.1–4 The direct band gap (1.04–2.50 eV), high absorption
coefficients, good radiation stability, non-toxic nature and low
cost, make these compounds suitable candidates for the fabri-
cation of next generation PV devices.2,5–8 In particular, the
CuInSe2 (CIS) semiconductor with a band gap of 1.04 eV and
absorption coefficient of the order of 105 cmꢀ1 for photons,9 is
being considered as the nearest competitor to the Si-based PVs in
the market.1,4 However the CIS based PV devices were fabricated
employing vacuum- and energy-demanding processes, thus
hindering its commercialization.1,10 In the last decade, solution-
based processes, screen printing, spray printing have evolved as
alternative technologies for making low-cost solar cells.8 More-
over, the morphology and size of the pyrolyzed materials can be
better controlled by the colloidal synthesis of nanoparticles than
by the chemical vapour deposition (CVD) method.2
morphology of the particles.1,7,10–12 The various solution-based
methods such as solvothermal, electrodeposition and spray
pyrolysis used three different sources of precursors to synthe-
size the CIS materials, which can affect the cell performances
depending on the nature of absorbing layer.10 The solvothermal
route under mild reaction conditions using single-source
precursors (SSPs) has emerged as highly efficient tool for the
controlled preparation of nanostructures. Since the rst report
of [(PPh3)2CuIn(SEt)4] in 1993 by Hirpo et al.,13 the complexes of
the general formula [(PR3)nCuM(ER0)4] (R, R0 ¼ alkyl, aryl)5,13–16
have been extensively investigated as SSPs for the preparation of
thin lm of CuME2 using CVD technique. A few such SSPs have
also been used to prepare the nanoparticles of CuME2 at
reduced temperature.2,3,5 The organic groups R, R0 play signi-
cant role in determining the solubility, structure and also the
decomposition process of the complex, which affects the phase
purity of the semiconductor materials.
We have recently synthesized the complexes of Cu(I) and
In(III)
metals,16 using the hybrid ligands amino-
alkylselenolates17,18 and 4-pyridylselenolates19,20 and prepared
the binary copper and indium selenides. The hard donor N
atom present in the above ligands, inhibited to form the SSPs
containing Cu, In and Se element, either by chelating or
bridging with metal centers thus forming co-ordination poly-
mers. However, the ternary CuInSe2 was prepared using two
source precursors. To prepare the SSPs for CIS nanomaterials,
next we sought to explore the ligand Bz2Se2 which is photo-
sensitive21 and known for clean-cleavage of benzyl group (Bz ¼
CH2Ph).22 Herein, we describe the synthesis and structural
aChemistry Division, Bhabha Atomic Research Centre, India. E-mail: dsandip@barc.
gov.in
bMechanical Metallurgy Division, Bhabha Atomic Research Centre, India
cRadiation Biology and Health Sciences Division, Bhabha Atomic Research Centre,
Mumbai 400 085, India
† Electronic supplementary information (ESI) available: Details of
crystallographic procedure and structure renement data table of
[(PPh3)2CuIn(SeCH2C6H5)4]. 1H and 31P{1H} NMR spectrum and TGA curve of
[(PPh3)2CuIn(SeCH2C6H5)4], XRD patterns, SEM images, EDX spectrum and
TEM images of CuInSe2. CCDC 1911532. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c9ra03429c
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characterization of [(PPh3)2Cu(m-SeCH2Ph)2In(SeCH2Ph)2],
which has been used as SSP for the preparation of single phase
CuInSe2 nanoparticles by solvothermal method. The particles
were characterized by powder X-ray diffraction (XRD), scanning
electron microscopy with energy dispersive X-ray (SEM-EDX)
analysis, high-resolution transmission electron microscopy
(HRTEM) and diffuse reectance spectroscopy (DRS).
Results and discussion
Syntheses and NMR spectroscopy
The complex has been synthesized by modifying the proce-
dure reported by Kanatzidis,13 using mixture of CuCl and
PPh3 instead of [(Ph3P)2Cu(CH3CN)2][PF6]. The complex
[(PPh3)2CuIn(SeCH2C6H5)4] has been synthesized by the
addition of CuCl and PPh3 to a freshly prepared Na-salt of
anionic complex of In(III) prepared from InCl3 and four
equivalents of Na-salt of benzylselenolate ligand (Scheme
1).23 This complex has been characterized by elemental
analysis and NMR spectroscopy. The microanalysis and
1
integration of the H NMR peaks of the complex suggest the
Fig. 1 Molecular structure of [(PPh3)2CuIn(SeCH2C6H5)4].
phosphine and selenolate ligands are in 1 : 2 ratio, con-
forming the formula [(PPh3)2CuIn(SeCH2C6H5)4]. The
mononuclear structure has been conrmed by the single
crystal X-ray structure. The 1H NMR spectrum exhibits one
set of signals for all the selenolato groups in solution. A
singlet at d 3.77 ppm was observed for SeCH2 group in 1H
NMR spectra (Fig. S1, ESI†). The broad singlet was observed
at ꢀ4.1 ppm in 31P{1H} NMR recorded in CDCl3 solvent
(Fig. S2, ESI†). The complex is soluble in chloroform,
dichloromethane and acetonitrile, but insoluble in
methanol.
In contrast to the complexes of Cu and In using ethyl
selenolate/phenyl selenolate,5,13,15 the pyridylselenolates of
Cu and In do not react with each other to form heterometallic
chalcogenolates.16 This non reactivity can be attributed to the
presence of the pyridine donors, which compete effectively
with bridging selenolate ligands for access to the metal
coordination sphere to form molecular indium compounds
and to the stabilizing inuence of the Cu–Cu bonds in the
copper compounds.
shown in Fig. 1 and the selected inter atomic parameters are
given in Table 1. The structure of the complex reveal the
monomeric form of [(Ph3P)2Cu(m-SeCH2Ph)2In(SeCH2Ph)2].
The tetrahedral Cu(I) and In(III) metals are linked by two
bridging benzyl selenolate ligands, forming
a planar
“CuSe2In” ring. Other two terminal positions of the metal
centers are coordinated by two PPh3 and two benzylseleno-
late groups. The inner angle Se1–In–Se1i (98.0ꢁ) of the
“CuSe2In” ring and outer angle Se2–In–Se2i (111.1ꢁ) formed
by the terminal selenolate groups are less deviated from the
ideal tetrahedral angle in comparison to the corresponding
angles (96.1 and 116.6) in the reported complex [(Ph3P)2Cu(m-
SePh)2In(SePh)2].15 The spacer CH2 group of the benzylsele-
nolate ligand in the present complex helps to minimise the
steric repulsion between the bulkier groups which is man-
ifested in the reduced non-bonded Cu/In distance of about
˚
3.35 A, compared to analogous phenyl selenolate complex
15
˚
(3.50 A). The benzyl groups adopt anti conformation and
a two-fold symmetry axis exist along the Cu–In bond in the
molecular structure. As expected the tetrahedral Cu center is
more distorted due to the two bulkier phosphines as revealed
by the P1–Cu–P1i angle measuring 122.2ꢁ. The In–Se bond
Crystallography
Molecular structure of [(PPh3)2CuIn(SeCH2C6H5)4] has been
established by single crystal X-ray diffraction analyses. The
ORTEP drawing with crystallographic numbering scheme is
˚
distances (2.62 A) for the bridging selenolates are longer than
the corresponding distances for the terminal selenolates
Scheme 1
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Table
[(PPh3)2CuIn(SeCH2C6H5)4]
1
Selected bond lengths (A˚) and angles (o) for
In1–Se1
2.6225 (13)
In1–Se2
In1–Se2i
Cu1–Se1i
Se2–C7
2.5483 (13)
2.5483 (13)
2.5624 (16)
1.992 (14)
2.290 (2)
In1–Se1i
2.6225 (13)
2.5623 (16)
1.995 (14)
2.290 (2)
Cu1–Se1
Se1–C8
Cu1–P1
Cu1–P1i
Cu1/In1
Se1–In1–Se1i
Se2–In1–Se2i
Se1–Cu1–Se1i
P1–Cu1–Se1
P1–Cu1–Se1i
P1–Cu1–P1i
3.347
98.02 (6)
Se1–In1–Se2
Se1–In1–Se2i
Cu1–Se1–In1
P1i–Cu1–Se1
P1i–Cu1–Se1i
113.36 (4)
110.21 (4)
80.41 (5)
114.04 (7)
101.92 (7)
111.11 (7)
101.17 (8)
101.92 (7)
114.04 (7)
122.19 (14)
(2.55 A) and are in agreement with earlier reports.15,16,24,25 The
˚
˚
Cu–Se bond distances (2.56 A) are in the range of reported
Fig. 2 The PXRD pattern of CuInSe2 obtained from thermolysis of
[(PPh3)2CuIn(SeCH2C6H5)4] in oleylamine at 300 ꢁC for 30 min.
values.15,16,24
Thermal studies
centered tetragonal phase, conrmed by powder XRD (Fig. 2)
(JCPDS le no. 81-1936). The broadening of the peaks
suggests the formation of nanoparticles with the average size
of ꢂ15 nm, calculated using the Debye–Scherrer formula. The
EDX of the black powder showed the presence of Cu, In and
Se atoms (Table 2 and Fig. S7, ESI†). The SEM taken at
different resolutions (Fig. S8, ESI†), showed large aggregates
of CuInSe2 nanocrystals. The TEM image of the CuInSe2
nanoparticles showed irregular shapes with size in the range
of 10–25 nm (Fig. 3(a)). The high-resolution TEM (HRTEM)
image of CuInSe2 nanoparticle is displayed in Fig. 3(b). The
observed inter-planar spacing of 0.34 nm is complied with
the (112) lattice spacing of CuInSe2 nanoparticles. The ring-
type selected area electron diffraction (SAED) pattern
(Fig. 3(c)) from the particles corroborated their nanocrystal-
line nature.
Thermolysis of [(PPh3)2CuIn(SeCH2C6H5)4] in HDA at
300 ꢁC for 30 min, resulted in a black powder, the XRD
conrmed body centered tetragonal phase of CuInSe2
(Fig. S9, ESI†) (JCPDS le no. 81-1936). The broadening of the
peaks suggests the formation of nanoparticles with an
average size of ꢂ15 nm calculated using the Debye–Scherrer
formula. The EDX of the black powder showed the presence
of Cu, In and Se atoms (Table 2) (Fig. S10, ESI†). The scanning
electron micrographs (SEM) taken at different resolutions
(Fig. S11, ESI†), showed large aggregates of nano-crystalline
To assess the suitability of the complex as precursor for the
preparation of CuInSe2, thermo-gravimetric analysis of
[(PPh3)2CuIn(SeCH2C6H5)4] was carried out up to the
temperature 800 ꢁC under a owing argon atmosphere
(Fig. S3, ESI†). The complex underwent nearly one step of
decomposition with the formation of a black residue. At the
end of decomposition at approximately 375 ꢁC, the weight
loss found is ꢂ75%, whereas the calculated weight loss is
75.7% for the formation of CuInSe2. The complex [(PPh3)2-
CuIn(SeCH2C6H5)4] on heating in furnace at 400 ꢁC for 2 h
yielded a black residue (weight loss found 74.4%; calcd
75.7%), which was characterized as tetragonal CuInSe2 by
powder XRD (Fig. S4, ESI†) (JCPDS le no. 75-0107). The XRD
pattern of the residue obtained on furnace heating showed
additional small intense peaks attributed to the planes (200)
and (211).13,26 These peaks are absent in the XRD pattern of
residues obtained from solvolysis of the precursor either in
OA or HDA attributing to the nano-crystalline nature of
residues. The energy dispersive X-ray analysis (EDX) of the
black powder obtained on furnace heating showed the pres-
ence of Cu, In and Se atoms (Table 2) (Fig. S5, ESI†). The
scanning electron micrographs (SEM) taken at different
resolutions (Fig. S6, ESI†), showed large aggregates of
CuInSe2 micro-crystals.
Thermolysis of [(PPh3)2CuIn(SeCH2C6H5)4] in OA at 300 ꢁC
for 30 min, resulted a black powder of CuInSe2 of body
Table 2 The energy dispersive X-ray analysis (EDX) of the CuInSe2 obtained on thermal decomposition of [(PPh3)2CuIn(SeCH2C6H5)4]
Atomic ratio
Cu : In : Se
Atomic weight percentage found (calcd)
Experiment
Cu
In
Se
Furnace heating at 400 ꢁC for 2 h
Solvolysis in OA at 300 ꢁC for 30 min
Solvolysis in OA at 300 ꢁC for 10 min
Solvolysis in HDA at 300 ꢁC for 30 min
28.05 : 25.50 : 46.45 (1.10 : 1 : 1.82)
25.61 : 24.79 : 49.60 (1.03 : 1 : 2)
20.38 : 27.41 : 52.21 (1 : 1.34 : 2.56)
25.29 : 25.93 : 48.78 (1 : 1.03 : 1.93)
21.27 (18.90)
19.39 (18.90)
15.12 (18.90)
19.05 (18.90)
34.94 (34.14)
33.93 (34.14)
36.75 (34.14)
35.29 (34.14)
43.78 (46.96)
46.68 (46.96)
48.13 (46.96)
45.66 (46.96)
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Fig. 4 (a) TEM image, (b) SAED pattern of the CuInSe2 nanoparticles
obtained from thermolysis of [(PPh3)2CuIn(SeCH2C6H5)4] in hex-
adecylamine at 300 ꢁC for 30 min.
CuInSe2. The TEM image of the resultant CuInSe2 nano-
particles (Fig. 4(a)) show irregular shapes with size in the
range of 20–30 nm. The ring-type SAED pattern (Fig. 4(b))
from the particles corroborated their nanocrystalline nature.
The complex [(PPh3)2CuIn(SeCH2C6H5)4] on thermolysis in
oleylamine at 300 ꢁC for 10, 20 and 30 min time interval also gave
the tetragonal CuInSe2 as indicated by powder XRD (Fig. S12, ESI†).
The powder XRD pattern obtained for 10, 20 and 30 min are almost
similar in appearance and the size of the particles calculated using
the Debye–Scherrer formula are ꢂ20 nm. The EDX of the black
powder obtained in OA at 300 ꢁC for 10 min showed the presence of
Cu, In and Se atoms (Table 2) (Fig. S13, ESI†). The SEM taken at
different resolutions (Fig. S14, ESI†), showed large aggregates of
nano-crystalline CuInSe2.
Fig. 3 (a) TEM image, (b) HRTEM image, and (c) SAED pattern of the
CuInSe2 nanoparticles obtained from thermolysis of [(PPh3)2-
CuIn(SeCH2C6H5)4] in oleylamine at 300 ꢁC for 30 min.
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grade solvents were obtained from commercial sources. The
ligand (C6H5CH2Se)2 was prepared according to literature
method.30 Due to slow photo-decomposition of Bz2Se2, it was
recrystallized every month from hexane. Melting points were
determined in capillary tubes and are uncorrected. Elemental
analyses were carried out on a Thermo Fischer Flash EA1112
CHNS elemental analyzer. The 1H and 31P{1H} NMR spectra
were recorded on a Varian spectrometer operating at 500 and
242.9 MHz, respectively. Chemical shis are relative to internal
chloroform peak for 1H NMR spectra. Thermo gravimetric
analyses (TGA) were carried out on a Nitzsch STA 409 PC-Luxx
TG-DTA instrument, which was calibrated with CaC2O4$H2O.
ꢀ1
ꢁ
The TG curves were recorded at a heating rate of 10 C min
under a ow of argon. Powder diffraction X-ray pattern were
obtained on a Rigaku SmartLab X-ray diffractometer using
CuKa radiation. SEM and EDX measurements were carried out
on MIRERO Inc. AIS2100 and Oxford INCA E350 instruments,
respectively. The TEM investigations were carried out in a Libra
200FE instrument operated at 200 kV. Optical diffuse reec-
tance measurements in the region 200–1800 nm (0.68 eV to 6.2
eV) were conducted on a two-beam spectrometer (V-670, JASCO)
with a diffuse reectance (DR) attachment consisting of an
integration sphere coated with barium sulfate which was used
as a reference. Measured reectance data were converted to
absorption (A) using Kubelka–Munk remission function.31
Fig. 5 Plots of [F(R)hn]2 vs. energy generated by Kubelka–Munk
transformation of solid-state diffuse reflectance data CuInSe2 nano-
structures obtained by thermolysis of [(PPh3)2CuIn(SeCH2C6H5)4] in
OA at 300 ꢁC for a duration of 30 minutes.
Optical properties of CuInSe2 nanostructures
The optical band gap of CuInSe2 nanostructures has been
measured by solid state diffuse reectance spectroscopy (DRS)
applying Kubelka–Munk transformations. The plot of [F(R)hn]2
vs. hn, has provided the direct band gap value 1.86 eV for
Syntheses
CuInSe2,
obtained
on
thermolysis
of
[(PPh3)2-
ꢁ
CuIn(SeCH2C6H5)4] in oleylamine at 300 C (Fig. 5). Similarly,
[(PPh3)2CuIn(SeCH2C6H5)4]. To a freshly prepared NaSeCH2-
the direct band gap has been calculated as 1.85 eV for CuInSe2 C6H5 (from (C6H5CH2Se)2 (142 mg, 0.42 mmol) and NaBH4
obtained on thermolysis of [(PPh3)2CuIn(SeCH2C6H5)4] in hex- (33 mg, 0.87 mmol) in benzene/methanol (20 mL)) was added
adecylamine at 300 ꢁC (Fig. S15, ESI†) and matches well with the solid InCl3 (46 mg, 0.21 mmol) and stirred for 1 h. To this, CuCl
reported values.27 The direct band gaps of CuInSe2 nano- (21 mg, 0.21 mmol) and PPh3 (110 mg, 0.42 mmol) dissolved in
structures showed a blue shi compared to the bulk CuInSe2 i.e. dichloromethane/CH3CN (20 mL) was added, the stirring was
1.04 eV.28 The increase in band gap with decreasing particle size continued for 4 h. The reaction mixture was ltered through G3
may be either due to lattice distortions or surface lattice defect assembly, the off-white residue was washed with H2O, methanol
or quantum connement or surface effect of the carriers.29
(2 ꢃ 5 mL), and dried in vacuum to give the title complex (yield
ꢁ
176 mg, 61%), mp 161 C. Anal. calcd for C64H58CuInP2Se4: C,
1
55.57; H, 4.23%. Found: C, 55.16; H, 4.19%. H NMR (CDCl3):
Conclusions
d 3.77 (s, 8H, SeCH2); 7.12 (t, 3JHH ¼ 7.0 Hz, 12H, Ph); 7.16 (q, 3JHH
¼ 6.5 Hz, 8H, Ph); 7.22–7.25 (m, 24H, PPh); 7.34 (t, 3JHH ¼ 6.5 Hz,
8H, Ph) ppm. 31P{1H} NMR (CDCl3): d ꢀ 4.1 (br, s) ppm.
The stable hetero-bimetallic complex of copper and indium
metals of benzylselenolate ligand is conveniently synthesized,
which can be used as SSP for the preparation of CuInSe2. The
mononuclear structure of the complex reveals the monodentate
and bridging mode of selenolate ligands. On thermolysis in
oleylamine or HDA, the complex yielded pure-phase of CuInSe2
nanocrystals, which showed the band gap of 1.86 and 1.85 eV,
respectively. The morphology and composition of nano-
structures have been investigated by pXRD, SEM, TEM and EDX
analysis.
Preparation of CuInSe2 by solvothermal method
The complex [(PPh3)2CuIn(SeCH2C6H5)4] (95 mg) was added in
oleylamine/HDA (ꢂ5 mL) preheated at 300 ꢁC with vigorous
stirring under owing argon and continued for 30 minutes. The
reaction temperature was rapidly brought down to 60 ꢁC and
was quenched by injecting 10 mL of methanol. The resulting
residue, thus obtained was separated by washing with excess
methanol followed by centrifuging and drying under vacuum to
obtain black powder.
Experimental section
Materials and methods
All the reactions were carried out in Schlenk asks under
a nitrogen/argon atmosphere. Indium trichloride, CuCl, PPh3,
Conflicts of interest
NaBH4, oleylamine (OA), hexadecylamine (HDA) and analytical There are no conicts of interest to declare.
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15 J. Masnovi, K. K. Banger, P. E. Fanwick and A. F. Hepp,
Polyhedron, 2015, 102, 246–252.
Acknowledgements
16 M. K. Pal, S. Dey, A. P. Wadawale, N. Kushwah, M. Kumar
and V. K. Jain, ChemistrySelect, 2018, 3, 8575–8580.
17 S. Dey, V. K. Jain, S. Chaudhury, A. Knoedler, F. Lissner and
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We thank Mr Asheesh Kumar of Chemistry Division for the
measurement of SEM and EDX.
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