Towards toxicity removal in lead based perovskite solar cells by compositional gradient using manganese chloride

Article abstract of DOI:10.1039/c6tc00650g

We report synthetic steps towards a lead free manganese based perovskite MAPb_xMn_1-xI_1+2xCl_2-2x (nominal x = 0.1-1.0), photovoltaic material via a solid state reaction. Further application as an excellent panchromatic light harvester involves the fabrication of a cell with an inverted planar architecture at low processing temperature. This novel perovskite material offers an outstanding V_oc of 1.19 V with fill factor of 87.9%.

Full text of DOI:10.1039/c6tc00650g

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Towards Removal of toxicity from Lead based perovskite Solar
Cell by Compositional Gradient using Manganese Chloride
Received 00th January 20xx,
Accepted 00th January 20xx
Pallavi Singh, Prem Jyoti Singh Rana, Pankul Dhingra and Prasenjit Kar*
DOI: 10.1039/x0xx00000x
www.rsc.org/
We report synthetic steps towards lead free manganese based does not pose toxic threat.
perovskite MAPb 0.1-1.0),
In this communication, we report for the first time, the
x
Mn1-x
I1+2xCl2-2x (nominal
x
=
photovoltaic material via solid state reaction. Further synthesis, characterization and fabrication of a manganese
application as an excellent panchromatic light harvester involve based lead free mixed halide perovskite with chemical formula
cell fabrication with inverted planar architecture at low CH
3 3 x
NH Pb Mn1ꢀxI1+2xCl2ꢀ2x. In order to investigate the structure
processing temperature. This novel perovskite offer an of the material synthesized, XꢀRay Diffraction measurements
outstanding Voc of 1.19 V with Fill Factor 87.9%.
were performed. The diffraction pattern is in good agreement
with the data reported for the tetragonal conformation (Space
The last straw concerned with commercialisation of modern group I4/mcm, Z=4) of the perovskite structure and the
1
1,12
organic and inorganic photovoltaic is higher cost processing structure obtained is identical to the CH
3
NH
and overpricing. In this regard cost effectiveness and ease of The measured XRD pattern indicates splitting of diffraction
processing is the main consequence of forefront of Organicꢀ reflections at 13.95
and 14.06 value is due to (002) and
Inorganic hybrid perovskites. It was successfully incorporated (110) plane. Splitted peak around 28.13
and 28.40 value is
assigned for (004) and (022) plane of perovskite. The peak at
structure 31.64
, 31.83 , 40.43 and 43.11 value is related to (114),
octahedra network. Here, A is a cation (310), (224) and (330) plane of perovskite (Fig. 1a and b).
3 3
PbI structure.
1
º
º 2ꢀ
º
º 2ꢀ
2
as hole transporting materials in third generation photovoltaics.
The OrganicꢀInorganic hybrid perovskites have ABX
with corner sharing BX
+
3
º
º
º 2ꢀ
6
+
+
such as Cs or a small molecule like CH NH
, (HC(NH ) ) Presence of all these lattice plane ensures the Tetragonal
3
3
2 2
which not only maintain total charge balance but also influence CH NH PbI Upon addition of manganese chloride (MnCl ) to
3
3
3.
2
3
,4
the crystal structure there by tune the band gap.
X is likely the lead based perovskite, very slight shift in 2
ꢀ
value is
ꢀ
ꢀ
ꢀ
2+
Cl , Br ,I or a mixture of halides. B is more oftenly Pb . observed along with consistent decrease in the lattice parameter
Although hazardous environmental aspects of associated lead a and c which indicates the formation of a solid solution
creates additional roadblocks in the development of this (Table.1). This slight decrease in lattice parameter leads to very
yardstick CH NH PbI . Efforts have been made to substitute meager change in volume across the series. It can be seen from
3
3
3
2
+
2+
2+ 5,6
Pb with same group elements like Sn , Ge . However, Fig. 1c that the MAPb Mn1ꢀxI Cl2ꢀ2x solid solution is in
x
1+2x
.13
2
+
2+
Sn and Ge have addressed the stability issues due to ease of agreement with Vegard’s law
oxidation in 4+ state under ambient conditions that break down progressively decreases with addition of MnCl due to small
The lattice parameters
2
2
+
2+
perovskite structure along with formation of oxide and ionic radius of Mn with respect to Pb . A prominent change
hydroxide of tin metal. This drags the research community to in the peak intensity, however, is evident. This can be attributed
5
envaisage on other substitute of lead. Recent studies show to the loss of crystallinity of the structure upon addition of
2
+
2+
2+
2+
incorporation of Cu , Ca , Cd and Sr metals cations as manganese. Furthermore, it can be observed that the intensity
alternatives, are attracting a great intereset to the scientific of the peaks is doubled from x= 0.8 to x= 1.0. Study of the
7
,8
3 3 3
communities. Studies involving CH NH SrI stated different remaining composition is shown in (Fig. S2 ESI†).
bonding pattern of MꢀX bond that impedes intercalation of Structural similarity of this novel perovskite with standard
+
CH NH which is basic framework of CH NH PbX with band perovskite CH NH PbI opens the area for further analysis.
3
3
3
3
3
3
3
3
9
gap of 3.6eV makes it inappropriate absorber. Attempts have Optical characterization of the synthesized perovskite was
been made to swap the lead through split an ion approach using performed by UVꢀVis spectroscopy and Photoluminescence
Bi and chalcogenide such as S, Se. Taking this into measurements. It is observed that the film exhibits a broad
consideration there emerges an urgent need to propose a absorption spectrum in the NIR spectral range therefore is a
perovskite material constituting a metal ion moiety which is strong panchromatic absorber. The absorption onset for x = 1
1
0
stable under ambient conditions, is abundantly available and lies at 816 nm and sucessive addition of MnCl leads to blue
2
shift of the absorption onset with wavelength 796 nm for x =
0
.1(Fig. 2a). It can be seen from UVꢀVis data that the bandgap
increases upon increasing the MnCl content in the perovskite.
2
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x
Fig. 1 (a) Xꢀ Ray Diffraction plots of the MAPb Mn1ꢀxI1+2xCl2ꢀ2x system as a function of x. (b) Enlarge view from 25ꢀ35 2ꢀ value.
(c) Variation in lattice parameter a as a function of x.
The increase in the bandgap can also be associated with the CH
3
NH
3
PbI
3
. Study of the remaining composition is shown in
substitution of iodine ions by chlorine ions. A marginal increase in (Fig. S3 ESI†)
4
.0
3.5
.0
.5
0.10
the bandgap has an associated advantage of reduced quantity of lead
which is 1/10 of the initial. Hence change in elemental composition
a
X=0.2
X=0.4
X=0.6
X=0.8
X=1.0
th
0.08
3
accompanied by crystal distortion which is responsible for tuning of
band gap as compared to standard CH NH PbI .
2
x= 0.1
x= 0.2
x= 0.3
x= 0.4
x= 0.5
x= 0.6
x= 0.7
x= 0.8
x= 0.9
x= 1.0
0.06
0.04
0.02
0.00
3
3
3
2.0
1.5
1.0
The room temperature photoluminescence peak of the
standard CH NH PbI is centered at 753nm. The peak maxima
3
3
3
0.5
occur at approximately the same value of wavelength
irrespective of the composition (Fig. 2b). It should be observed
that the substitution of iodide ions by chlorine ions, according
to the previous reports, is expected to increase the bandgap of
the perovskite. But the emission peak does not face a shift upon
addition of manganese chloride as one of the initial compounds.
Change in the composition is not well reflected in the
Photoluminescence spectra. Study of the remaining
composition is shown in (Fig. S4b ESI†).
0
.0
400
500
600
700
800
740
745
750
755
760
765
770
Wavelength (nm)
Wavelength (nm)
x = 1.0
c
x = 1.0
x = 0.8
x = 0.6
x = 0.4
x = 0.2
100
x = 0.8
x = 0.6
x = 0.4
x = 0.2
d
7
5
5
0
25
In case of polycrystalline material UVꢀVis absorption
spectra does not give precise band gap measurement. Here
transmitted radiation intensity not only depend on absorption
due to optical band gap but also on light scattered by material &
absorption due to intrinsic defect in semiconductor. Therefore
we have performed Diffusion Reflectance Spectra (DRS) (Fig.
400
500
600
700
800
900
1.45
1.50
1.55
Energy (eV)
1.60
1.65
1.70
Wavelength(nm)
e
x
=
1.0
x
=
0.8
x
x
=
=
0.6
0.4
2
c) to calculate the optical absorption coefficient (
α
) using
x
=
0.2
KubelkaꢀMunk relationship according to the equation K/S =
2
(1ꢀR) /2R= F(R)= α. Here, K and S are the KubelkaꢀMunk
3
500
2800
2100
1400
700
-
1
absorption and scattering coefficient respectively. F(R) is the
KubelkaꢀMunk function and R is the percentage of reflected
light. The optical bandgap is depicted by the transformed
Wavenumber (cm )
1
4
p
Fig. 2 a) Absorption Spectra b) Photoluminescence Spectra (c)
Diffusion Reflectance Spectra d) Tauc plot e) Fourier Transform
Infrared Spectroscopy of MAPb Mn1ꢀxI1+2xCl2ꢀ2x as a function of x.
x
KubelkaꢀMunk function [F(R)hv] = A(hv ꢀ E ). Here E is
g
g
the bandgap energy. In case of a direct allowed transition, p
transition probability) attains a value of 2 or 2/3 where
(
indirect allowed transition considers 1/2 or 3/2 values for p.
The optical bandgap is obtained by extrapolating the linear part
of the [F(R)hv] plot, also known as the Tauc plot.
It is assumed that the synthesized perovskite is having
direct bandgap. It can be observed from (Fig. 2d) that band gap
x
for all compositions of MAPb Mn1ꢀxI1+2xCl2ꢀ2x (i.e., x=0.1ꢀ1.0)
Fourier Transform Infrared Spectroscopy (FTIR) of the perovskite
materials for different values of x is performed at ambient
temperature shown in Figure (2e). Literature review evaluate that
low temperature orthorhombic form is preferred over tetragonal and
cubic form due to less angular fluctuation. Shift in peak position
for different composition as a function of varying degree of
interaction between organic moiety and inorganic cage can be well
2
15
16
ranges from 1.56eV to 1.54eV compared to 1.56eV for standard
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ꢀ
1
ꢀ1 17
explained by taking region 800cm ꢀ 3100cm . This region is
primarily used for internal vibration of Methyl ammonium cation.
+
(
(
a)
b)
ꢀ
1
ꢀ1
3 3
The peak at around 913 cm and 1268 cm assigned for CH NH
ꢀ1
ꢀ
1
rocking vibration. The peak centered at 1374 cm and 1465 cm
+
3
denoted for symmetric CH
3
and NH
bending respectively. The
ꢀ
1
+
3
peak corresponds to 1624 cm in due to asymmetrical NH bending.
ꢀ
1
ꢀ1
The peak broadening from 2800 cm ꢀ3600 cm comprise symmetric
+
+
and asymmetric NH
3
stretching. The peak for symmetric NH
stretching around 3136 cm is more prominent for CH
3
ꢀ1
3
3 3
NH PbI . It
can be clearly seen that there is no observable change in the IR
spectra on decreasing the polarisibility by successive decrease in
1
8
values of x or Iodide ion (according to LorentzꢀLorenz shift).
Study of the remaining composition is shown in (Fig.S4 ESI†)
Table. 1 Nominal value for Manganese in contrast to the
experimental value obtained by the EDX analysis, lattice
parameter
Nominal
Value
Experime-
ntal Value
(1-x)
Lattice
Parameters
a (Å)
Lattice
Parameter
c (Å)
E
g
(DRS)
(
1-x)
0
0
10.1243
10.0866
10.0491
10.0367
10.0201
12.8067
12.7589
12.7115
12.6958
12.6749
1.56
1.56
1.54
1.56
1.55
0.2
0.183
0.3605
0.575
0.788
0.4
0.6
0.8
EDX analysis was performed for different values of x in the
perovskite MAPb Mn Cl2ꢀ2x. shown in Table S1. It state that
I
1ꢀx 1+2x
x
upon decreasing the value of x from 1.0 to 0.2, the amount of lead
incorporated in the material decreases from 30.58 weight percent to
0
.72 weight percent. Thus, the amount of lead incorporation in the
perovskite material has been reduced by a factor of 43. Furthermore,
it can be seen that the amount of manganese incorporation increases
from 0 to 21.41 weight percent in x=1 and x=0.2 samples
respectively. The abundance of manganese incorporation is depicted
by EDX mapping (Fig. 3).
A consistent trend in the particle size, however, cannot be
observed from the FESEM images of the perovskite powder.
Clearly resolved crystals can be observed from the FESEM
images of perovskites corresponding to
x = 1.0 ꢀ 0.5
respectively. But, as the amount of manganese in the perovskite
material increases beyond x=0.5, i.e, for x= 0.4 to 0.1, separate
crystals are no longer observed and infact highly diffused
crystals were obtained with sharing common boundaries. Study
of the remaining composition is shown in (Fig.S5 and S6 ESI†)
Furthermore, it must be noted, that for x=0, a stable perovskite
structure is not obtained by the aforementioned procedure.
Thus, it can be concluded that beyond x=0.5, the addition of
increasing amounts of manganese chloride decreases the
stability of the proposed material under ambient conditions. Fig.
x
3 (a) Photograph of MAPb Mn1ꢀxI1+2xCl2ꢀ2x with x
The results, however, may prove to be different under inert decreasing from 1 ꢀ 0.1. (b) FESEM images of the synthesized
conditions for preparation of the material. Table (1) shows the perovskite for different values of x along with the EDX plots
manganese incorporation in few samples, i.e., x=0.2, 0.4, 0.6 and EDX mapping showing the incorporation of lead and
0
x
.8, 1.0 that have the experimental value for (1ꢀx) is close or manganese in MAPb Mn1ꢀxI1+2xCl2ꢀ2x.
less than the nominal value derived form weight% depicted
EDX analysis.
The cross section of fabricated cell shows ~ 45nm thick layer of
Fig 4 shows photovoltaic performance of fabricated device hole transporting material (HTM) PEDOT:PSS just above the ITO
based on inverted planar architecture ITO/PEDOT:PSS/MAPb
Mn1ꢀ film followed by ~125nm thin layer of MAPb
perovskite which was completely covered by around 150nm thick
x
Mn1ꢀxI1+2xCl2ꢀ2x
x
x
I1+2xCl2ꢀ2x/PC61BM/Al (x=0.9) under Air Mass 1.5 Global with an
2
irradiation intensity of 100 mW/cm . It displays an alarming open layer of PC61BM as a electron tansporting material (ETM).
circuit voltage Voc and Fill factor (FF) of 1.19V and 87.9%
respectively. Unfortunately the obtained energy conversion
efficiency of 0.32% is a cause of flat shortꢀcircuit current of 15.146
1
9
µA which is consistent with previous reports.
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Fig. 4. (a) Device architecture of ITO/PEDOT:PSS/ MAPb
structure of MAPb
1+2xCl2ꢀ2x. perovskite solar cells. (c) Current−voltage curves of MAPb
.9 (d) Top morphology of perovskite film on ITO/PEDOT:PSS substrates.
x
Mn1ꢀx
I
1+2xCl2ꢀ2x/PC61BM/Al (b) Crossꢀsectional SEM image showing the device
x
Mn1ꢀx
I
x
Mn1ꢀxI1+2xCl2ꢀ2x. perovskite solar cells x =
0
We have used only 15wt% of perovskite (1:1 ratio) solution for 3. (a) P. Gao, M. Grätzel and M. K. Nazeeruddin, Energy Environ.
Sci., 2014,
Kar, Energy Technol., 2016, DOI:10.1002/ente.201500534.
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device fabrication that give a very thin layer of perovskite ~125nm.
This gives insufficient charge carrier generation as a consequence
low short circuit current Isc is observed. In this way there is less
charge carrier generation due to insufficient thickness of absorber
layer which greatly suppress the device efficiency. Here the
outastanding fill factor is achieved due to complete surface coverage
of perovskite layer which leads to high shunt resistance (Rsh). The
4
.
7
5
device surged in term of Voc (1.19V) which is attributed to pin hole 6. D. Sabba, H. K. Mulmudi, R. R. Prabhakar, T. Krishnamoorthy, T.
free morphology of top layer that inturn reduce recombination to an Baikie, P. P. Boix, S. Mhaisalkar and N. Mathews J. Phys. Chem. C,
appreciable extent (Fig 4d). It may be one of the highest Voc 2015, 119, 1763.
7
. D. Cortecchia, H. A. Dewi, J. Yin, A. Bruno, S. Chen, T. Baikie, P.
reported yet via inverted planar architecture over other bilayered
HTM that incorporate polymer additive to increase the work
function of HTM in order make perfect ohmic contact.
P. Boix, M. Grätzel, S. Mhaisalkar, C. Soci, and N. Mathews Inorg.
Chem., DOI: 10.1021/acs.inorgchem.5b01896.
2
0
8
. J. Navas, A. S. Coronilla, J. J. Gallardo, N. C. Hernández, J. C.
Experiments with other composition is in their preliminary stage. we Piñero, R. Alcántara, C. F.Lorenzo, D. M. D.l. Santos, T.
have fabricated cell considering composition X=0.8 achieved ƞ Aguilar and J. M.Calleja, Nanoscale, 2015, , 6216.
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and X Tao, Cryst Eng Comm., 2015, 17, 665.
7
9
0
.83% , Voc 0.88 V, fill factor 19.2% but is still under optimisation.
There is plenty of room available for further invesigation such as to
explore the interfacial engineering of synthesized perovskite and
HTM/ETM interfaces. This communication may lead to deeper
insight due to presence of observable amount of Chlorine which is
1
1
one of the most debatable among scientific community. Since we 12. J. S. Manser, B. Reid and P. V. Kamat, J. Phys. Chem. C, 2015,
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2
1
004, 237, 363.
inert condition makes it unprecedented absorber.
4. H. S. Kim, C. R. Lee, J. H. Im, K. B. Lee, T. Moehl, A. Marchioro,
We thank Prof. Pradipta Banerjee, Director, Indian Institute
of Technology Roorkee, India for his constant support and
S. J. Moon, R. H. Baker, J. H. Yum , J. E. Moser , M. Grätzel and N. G.
encouragement. The authors would also like to thank Dr. Park, Sci. Rep., 2012, doi:10.1038/srep00591.
Saumya Dutta, Department of Electrical Engineering, IIT 15. J. Tauc, R. Grigorovici, and A. Vancu, Phys. Status Solidi, 1966,
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5, 627.
Madras for performing IꢀV Measurement. P.K gratefully
acknowledges the Department of Science and Technology
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(SB/FT/CSꢀ135/2012), New Delhi, India and Council of
1
Scientific and Industrial research (01(2796)/14/EMRꢀII) for
financial support. PJSR and PS acknowledge MHRD, India, for
their junior research fellowship.
1
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9. C. Zuo and L. Ding , Nanoscale
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| J. Name., 2012, 00, 1-3
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The graphical and textual abstract
Here we put a step toward swapping of toxic lead from lead based perovskite solar cell through
compositional change using Manganese Chloride as a substitute with a formula of MAPb Mn
x
1-
I
Cl2-2x (nominal x = 0.1-1.0). Further cell fabrication with inverted planar architecture at low
x 1+2x
processing temperature shows potential application towards future perovskite solar cell.