Accepting to Donate: NDI-Based Small Molecule as a Donor for Bulk Heterojunction Binary Solar Cells

Article abstract of DOI:10.1002/ejoc.201901615

A small molecular D-π-A-π-D triad NDIP consisting of naphthalenediimide (NDI) as an acceptor and porphyrin as a donor was synthesized. NDIP exhibits an intense absorption from visible to NIR region (400 nm to 1000 nm) with high molecular extinction coefficient. Endowed with excellent absorption and good charge carrier mobility, the molecule was used as a donor, against the normal perception as an acceptor due to the electron-deficient nature of NDI, in the binary bulk heterojunction solar cells with PCBM as an acceptor. The cell demonstrated remarkable power conversion efficiency of 8.45 % with extremely low E_loss of 0.40 eV, which is also the best recorded for NDI based small molecule organic solar cells.

Full text of DOI:10.1002/ejoc.201901615

A Journal of
Accepted Article
Title: Accepting to Donate: NDI-based Small Molecule as a Donor for
Bulk Heterojunction Binary Solar Cells
Authors: Ruchika Mishra, Sujesh S, Archana VS, Ayushi Kaushik,
Gaurav Gupta, Rahul Singhal, Ganesh D Sharma, and
Jeyaraman Sankar
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201901615
Link to VoR: http://dx.doi.org/10.1002/ejoc.201901615
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10.1002/ejoc.201901615
European Journal of Organic Chemistry
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Accepting to Donate: NDI-based Small Molecule as a Donor for
Bulk Heterojunction Binary Solar Cells
Ruchika Mishra,*[a] Sujesh S,[b] Archana V. S., [b] Ayushi Kaushik,[b] Gaurav Gupta,[c] Rahul Singhal,[d]
Ganesh D Sharma* [c] and Jeyaraman Sankar*[b]
Dedication ((optional))
Abstract: A small molecular D--A--D triad NDIP consisting of
naphthalenediimide (NDI) as an acceptor and porphyrin as a donor
was synthesized. NDIP exhibits an intense absorption from visible to
NIR region (400 nm to 1000 nm) with high molecular extinction
coefficient. Endowed with excellent absorption and good charge
carrier mobility, the molecule was used as a donor, against the normal
perception as an acceptor due to the electron-deficient nature of NDI,
Porphyrins based macrocyclic donors linked to strong
acceptor are known to have panchromatic absorption, which is
extendable upto NIR and are among the most successful small
molecule donors in BHJOSCs.[5] Among the various acceptor
units known, arylenediimides are undisputed champions due to
their tuneable aromatic core, their remarkable photophysical
properties, exceptional photo-chemical stability and high electron
in the binary bulk heterojunction solar cells with PCBM as an acceptor. mobility. These dyes are now been looked upon as the promising
The cell demonstrated remarkable power conversion efficiency of
8.45 % with extremely low Eloss of 0.40 eV, which is also the best
recorded for NDI based small molecule organic solar cells.
components in organic photovoltaics specially bulk heterojunction
solar cells wherein they act mainly as acceptor layer. However
recent studies have stressed that these dyes can be turned into
promising donor by appropriate functionalization.[5a] It is no
wonder that such synthetic tunablity has created a new upsurge
for developing these small molecules for extensive use in
widespread applications. Perylene-bisimides (PBIs) are well
known member of this class and extensive work has been done
on their core modification such as core-annulations, tethering
various chromophores onto the core and on the imide positions
are few to mention. There are many interesting reviews available
which highlight various synthetic strategies developed to fine tune
their architecture in accordance with the particular application.[6]
Naphthalenediimides, on the other hand is the lowest member of
this class[7], [8]and is a very good electron acceptor like its next
higher analogue i.e. PBI. Compared to PBIs, NDIs mainly absorbs
in UV region with low molar extinction coefficient values. This
property of NDIs makes them very much suitable for organic
transistor based applications. Noteworthy to mention here, this
class of molecule have good charge mobility and are versatile n-
type materials for organic field effect transistors (OFETs). There
are several reports available wherein NDI based polymers and
co-polymers were successfully exploited as charge transport
motifs.[9] However, due to their limited absorption in visible region,
NDIs are not usually considered as a very good candidate for
organic photovoltaics. Extension of conjugation in the aromatic
core is an important avenue to extend the light absorption up to
the visible region.
Introduction
The organic photovoltaics has gained tremendous attention
worldwide.[1] Especially, the developments in solution-processed
bulk heterojunction solar cells (BHJOSCs) based on small
molecules have accelerated and the power conversion efficiency
(PCE) of these BHJOSCs have been exceeded beyond 15%.[2],[3]
Also, focus has been shifted to develop new device configurations
and fabrication techniques in order to get enhanced PCEs. Light
harvesting efficiency (LHE) of the active layer throughout the solar
spectrum is a key factor in governing PCE in organic solar cells
(OSCs). Hence, low band gap materials containing strongly
electron donating core linked to an accepting unit through -
bridges are highly recommended owing to the intramolecular
charge transfer that often lowers the optical bandgaps of resulting
materials.[4]
[a]
[b]
Dr. R. Mishra,
Centre for Research on Environment and Sustainable Technologies,
IISER Bhopal, Bhauri, Bhopal, M.P. 462066 India
E-mail: ruchika@iiserb.ac.in
Mr. Sujesh. S, Ms. Archana V.S , Ms. A Kaushik and Prof. Dr. J.
Sankar,
Herein, we report the synthesis of a D-A-D type triad NDIP
constituted from porphyrin and NDI subunits. This D-A-D small
molecule showed very good solubility in most of the polar
solvents. Moreover, this triad exhibited intense absorption from
visible to NIR with high molar extinction coefficient. NDIP has a
narrow optical bandgap of 1.23 eV. HOMO and LUMO energy
levels of NDIP are -5.10 and -3.85 eV, making it suitable as an
electron donor when paired with PC71BM as acceptor for the
fabrication of solution-processed small molecule BHJ OSCs.
Therefore, we set out to explore NDI-Porphyrin chemistry in bulk
heterojunction solar cells. A simple, covalently-linked NDI-
Porphyrin unit is expected to absorb light intensity in a wide
Department of Chemistry
Indian Institute of Science Education and Research Bhopal
Bhopal Bypass Road, Bhauri, Bhopal, M.P. 462066 India
E-mail: sankar@iiserb.ac.in
https://www.jeyaramansankar.org
Mr. G. Gupta and Prof. G. D. Sharma
Department of Physics,
The LNMIIT (Deemed University), Jamdoli, Jaipur, Raj. 302031,
India
E-mail: gdsharma273@gmail.com
Dr. R. Singhal
Department of Physics, MNIT Jaipur, Raj. 302017, India
[c]
[d]
Supporting information for this article is given via a link at the end of
the document
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10.1002/ejoc.201901615
European Journal of Organic Chemistry
FULL PAPER
wavelength range that in turn will increase the PCE of the
proposed BHJ Solar cells. After optimizing the device
configuration, the OSCs showed overall PCE of 8.45 %, which is
one of the highest PCEs reported till date for any NDI-based small
molecule OSCs.
UV-Vis-NIR absorption Studies
Absorption spectra of NDIP is shown along with those of individual
chromophores i.e. porphyrin and NDI recorded in chloroform
(figure 1). NDIP shows a wide absorption in the UV-visible range,
which is further extended up to NIR region. Band positions and
molar extinction coefficients are listed in table 1. From the figure
1, it is clear that the synthesized triad exhibits a red shifted Soret
(~23 nm) with broadened Q bands, in comparison to reference
porphyrin. This can be understood in terms of extended 휋-
conjugation in the triad. The absorption spectrum features a
unique and broad charge transfer band in the range from 600 nm
till 950 nm, which can be attributed to an intramolecular charge
transfer between the porphyrin donor and NDI acceptor. Soret
band shows negligible shift in absorption maxima when measured
in different solvents. However, the CT band displayed noticeable
change in max with respect to the change in solvent polarity
(Figure S23).
Results and Discussion
1.2
1
0.8
0.6
0.4
0.2
0
NDIP (F)
350
500
650
800
950
1100
Wavelength (nm)
Figure 1. UV-vis-NIR absorption spectra of NDIP in comparison to NDI and
Porp in chloroform (left) and in thin film (right)
The red shift observed for bands in the spectra of thin film (Figure
1) indicates a stronger intermolecular - stacking and thus
aggregation in the film. The bandgap of NDIP is about 1.23 eV as
estimated from the absorption onset of thin film. The optical
bandgap of NDIP is narrower among most of the reported D-A-D
small molecules based on porphyrin donor units. It is due to an
enhanced -conjugation and ICT interaction between NDI core
and ZnPor end groups. This is further corroborated by the strong
absorption around the Q-band region of NDIP. This is crucial for
the photocurrent generation in NIR region to improve short circuit
current from the resulting OSCs.
Scheme 1. Synthesis of NDIP
General synthetic procedures
Current
molecular
triad
consisting
of
a
central
naphthalenediimide (NDI) moiety linked to two porphyrins through
an alkyne bridge (Scheme 1). NDI was synthesized from
commercially available precursor naphthalenedianhydride (NDA)
by a modified procedure and then converted to NDI-I2 by a
modified method in good yield. It was expected that the NDI-I2 will
be a better precursor for further functionalization on NDI core
compared to the NDI-Br2 derivatives. Moreover, the iodination
reaction is a straightforward method to obtain the precursor than
the more cumbersome bromination route. The other precursor
Porp-CH was synthesized using a series of reactions as
described in scheme 1. Desired molecular triad NDIP is
synthesized via a typical Sonogashira coupling reaction of NDI-I2
and Porp-CH using PdCl2(PPh3)2 and CuI as catalyst in the
solvents N,N-diisopropylamine (DIA) and tetrahydrofuran (THF).
Detailed procedures are included in experimental section. All the
porphyrin based precursors were characterized by NMR
spectroscopy and mass spectrometry. Current triad is stable even
upto 400 0C as revealed by DSC (Figure S22). Synthesis and
characterization are discussed in detail in the supporting
information.
Table 1. Optical and electrochemical data for NDIP
Hole
Mobility
(µh)
Electron
Mobility
(µe)
ε / 105
E1 1/2 red
E2 1/2 red
E3 1/2 red
E1 1/2 ox
E2 1/2 ox
max
(M-1
cm-1)
(nm)
cm2/Vs
cm2/Vs
(V)
(V)
436
(Soret)
778
4.4
0.6
-0.63
-0.99
-1.49
0.87
1.22
1.68* 10-4
2.51* 10-4
(CT))
Computational and electrochemical studies
Computational studies[10] were done using Gaussian09 software
revealed that HOMO is delocalized over porphyrin core and NDI
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10.1002/ejoc.201901615
European Journal of Organic Chemistry
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while LUMO is confined mainly on NDI with some contribution
from alkyne linkage (Figure 2 & Figure S24).
In order to examine the electrochemical behaviour of the triad,
cyclic voltammetry studies were carried out in dichloromethane.
From figure 2 and table 1 it is clear that current triad undergoes
three reversible reductions and two oxidations. NDIP is slightly
easier to oxidize and reduce compared to its porphyrin and NDI
constituents, thus hinting at more delocalized HOMO and LUMO
in NDIP.
The HOMO and LUMO energy levels calculated using the
onset of reduction and oxidation potentials[5b] from the cyclic
Figure 3. Current density (J)- voltage (V) curves under the illumination (left), .
IPCE curves (right) for the devices
voltammetric data are found to be -5.10 and -3.85 eV, respectively. The poor nanoscale morphology of the as cast cell is attributed to
The corresponding energy levels of PC71BM are -4.12 and 6.10
eV. The LUMO offset between the NDIP and PC71BM as obtained
is ~0.30 eV, approximately equal to the threshold value needed
for the exciton dissociation and charge transfer in the BHJ active
layer. Hence, NDIP can be an apt donor when paired with
PC71BM as an acceptor, for solution processed OSCs.
the moderate value of PCE obtained. This contributed to the
unbalanced charge transport within the BHJ film. It has been
shown that the use of solvent additives helps in improving the
overall PCE of the active layers.[6a] It was found in our case that 3
v% pyridine to the solvent as an additive showed a positive effect
on the PCE (7.47 %) with an enhancement in Jsc and FF. To
further enhance the PCE, a two-step annealing approach (TSA)[11]
involving thermal and solvent vapor was applied to the devices.
The TSA treated NDIP: PC71BM active layer OSC showed a PCE
of about 8.45 %. The values of other vital parameters were Jsc =
15.43 mA/cm2, Voc= 0.83 V and FF= 0.66 (figure 3 and table 2).
Collectively, this supports the need for a better nanoscale
morphology and molecular ordering of the active layer to obtain a
balanced charge transport.
The incident photon to current conversion efficiency (IPCE)
spectra (Figure 3) exhibited a wide photo-response from 350 nm
to 1000 nm, resembling the combined absorption features of both
PC71BM and NDIP. The IPCE features confirm that both the donor
and the acceptor in this case contribute to the photocurrent
generation. The IPCE values measured for TSA treated active
layer are higher compared to that for as cast device, indicating
that the exciton generation rate and charge transfer are more
efficient in TSA based OSCs. The values of Jsc estimated from
the integration of IPCE spectra are 11.29 mA/cm2 and 15.32
mA/cm2 for as cast and TSA treated OSCs, respectively. This in
turn correlates well to the values observed in J-V curves.
LUMO
HOMO
Figure 2. Cyclic Voltammogram of NDIP in comparison to NDI and Porp (left)
& HOMO and LUMO Energy levels deduced from TD-DFT
Further, we have recorded the PL spectra of pristine PC71BM and
its blend with NDIP and found that upon excitation at 400 nm, the
pristine PC71BM showed a strong PL peak around 700 nm which
is quenched after blending with NDIP, indicating efficient photo-
induced charge transfer (Figure S25).
Table 2. Key photovoltaic parameters of the devices under different
optimization conditions
Active layer
Jsc (mA/cm2)
Voc (V)
FF
PCE (%)
NDIP:PC71BM
(as cast)
NDIP:PC71BM
(Pyridine
11.38
0.86
0.43
4.23
(4.14)a
7.47
Photovoltaic properties
14.52
15.43
0.83
0.83
0.62
0.66
(7.38)a
NDIP and PC71BM were employed as donor and acceptor
respectively, to investigate the photovoltaic performance using
the BHJ active layer (See ESI for device configuration). The
Donor to acceptor weight ratio plays an important role and
therefore was carefully optimized and a weight ratio of 1:1.5 in
BHJ active layer resulted in the best photovoltaic performance,
additive)
NDIP:PC71BM
(Pyridine
additive +TSA
8.45
(8.37)a
a average of eight devices
under the reported conditions. Figure
3 shows the J-V
The charge carrier mobilities of blends were then evaluated by
space charge limited current model for hole only and electron only
devices (see ESI for fabrication details). The hole mobilities in as
cast and TSA treated active layers are found to be 7.28 x10-5
cm2/Vs and 1.68x10-4 cm2/Vs, respectively, whereas the electron
mobilities are 2.43 x10-4 cm2/Vs and 2.51 x10-4 cm2/Vs,
respectively (Figure 4a and b). Compared to electron mobility,
characteristics of the as cast OSC under illumination and the
photovoltaic parameters are summarized in table 2. The OSCs
processed with as cast NDIP:PC71BM active layer showed overall
power conversion efficiency of PCE = 4.23 % with open-circuit
potential (Voc) of 0.86 V, short-circuit current (Jsc) of 11.38
mA/cm2 and a fill factor (FF) of 0.43.
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10.1002/ejoc.201901615
European Journal of Organic Chemistry
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there is a significant rise in hole mobility. The electron to hole
mobility ratios are 3.34 and 1.49, respectively, for as cast and TSA
treated active layers indicating more balanced charge transport in
later.
To get more insight into the effect of TSA on the charge
dissociation and extraction mechanism we determined the
variation of photocurrent density (Jph) with respect to the effective
voltage (Veff) (Figure 4c). In general, it is assumed that at high Veff
(2V), the free charge carriers are extracted after the generation of
photogenerated excitons, and are collected at the electrodes. In
case of TSA, the Jph demonstrate a rapid increase toward
saturated state (Jphsat) at low Veff, indicating that the above
processes are found to be more efficient.
and photo-voltage decay characteristics, respectively, for the as
cast and TSA treated active layers ( Figures S28 & S29). The
charge extraction time is smaller for TSA treated active layer (0.28
s) than as cast (0.37 s), indicating faster extraction of charge
carrier after TSA treatment. The charge carrier lifetimes were
estimated by TPV under an open circuit condition The relatively
longer carrier lifetime of the device based on TSA treated active
(3.56 s) than as cast counterpart (2.64 s) implies less
recombination and contributes to higher FF.
An efficient solar cell should not only possess high Voc and
Jsc but also should have minimal energy loss (Eloss) associated
with it.[14] The Eloss of the OSC based on optimized active layer is
0.40 eV, which is also the lowest reported till date for NDI based
molecules for OSCs. It further corroborates that a low LUMO
offset of 0.27 is sufficient for the electron transfer from NDIP to
PC71BM. The dielectric constant (r) of the material is another
factor which governs the various loss processes inherently
associated with the solar cells. Higher value of r leads to the
reduction in the charge recombinations which in turn improves the
charge carrier extraction efficiency.[15], [16], [17] Therefore we set out
to measure dielectric constant for our system at different
frequencies ranging from 100-105 Hz (Figure S30). The average
values of r were nearly 4.09 which are slightly larger than the
common organic semiconducting materials (~3-3.5). The
increase in the r of the active layer indicates that a low value of
HOMO and LUMO energy offset is sufficient for the exciton
dissociation and lowering the values of various losses associated
with the cell. [18], [19]
(b)
(a)
(c)
(d)
Figure 4. (a) J-V characteristics for electron only devices (b) J-V characteristics
for hole-only devices, (c) Variation of Jph with Veff, (d) XRD patterns of as cast
and TSA treated active layer thin films.
In the case of as cast OSC, the poor exciton dissociation and
enhanced charge recombination before collection by the
electrodes lead to lower values of FF. This is demonstrated by the
Jph, saturating at around 1.58 V. Jphsat measured for as cast and
TSA are 13.08 mA/cm2 and 16.02 mA/cm2, respectively (Figure
4c). The maximum exciton dissociation rates (Gmax) for as cast
and TSA based OSCs are 0.95 x1028 m-3s-1 and 1.16x1028 m-3s-1,
respectively. The Pdiss/Pcoll of as cast and TSA processed devices
are 0.87/0.68 and 0.96/0.75, respectively. The increased Pdiss and
Pcoll values demonstrare that the exciton dissociation and charge
collection were enhanced by TSA treatment.
The charge carrier recombination mechanism was
investigated by analyzing the dependence of Jsc and Voc on the
illumination intensity (Pin) [12] (Figure S26 & S27). Jsc is
proportional to (Pin) , where  is the recombination constant. In
general, the  value closer to unity indicates a weaker bimolecular
recombination. The TSA treated OSCs exhibited very weak
bimolecular recombination with a  value close to 0.95 compared
to 0.88 for as cast. The slope from the plot of Voc vs Pin implies
trap-assisted or Shockley-Read Hall (SRH) recombination.[13] The
values of slopes for as cast and TSA are about 1.54 kT/q and 1.23
kT/q, respectively, indicating that the TSA treatment suppressed
the SRH effectively.
Figure 5. TEM images of as cast and SVA treated active layers of NDIP:PCBM.
Scale bar is 100 nm.
To determine the microstructural profile and to probe the the
crystallinity and stacking behavior of NDIP:PCBM active layers,
X-ray diffraction (XRD) patterns were recorded on thin films.
Figure 4d illustrates that both the active layers show three
diffraction peaks. An intense peak (100) located at 2 = 4.96 has
lamellar distance of 1.81 nm and is more intense in the SVA
treated layer. A (010) diffraction peak located around 2 = 22.98
(as cast) and and at 2 =24.07 (TSA treated) correspond to -
stacking distance of 0.39 nm 0.38 nm, respectively. In addition to
the above, a diffraction peak at 2 = 18.96 was also observed for
PC71BM. The increase in peak intensity after TSA treatment
indicates enhanced crystallinity and compact molecular packing.
The size of the crystallite was calculated using the Scherrer
formula (see ESI). For (100) reflection, the crystallite size was
To get information about the carrier extraction time and
charge carrier lifetime, we estimated the transient photocurrent
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10.1002/ejoc.201901615
European Journal of Organic Chemistry
FULL PAPER
found to be 5.03 nm and 7.75 nm respectively for as cast and TSA
treated active layers.
Synthesis of NDI-I2
mixture of Pentamethylcyclopentadienylrhodium(III)chloride dimer
A
For (010) reflection, the crystallite size for as cast active
layer is 5.41 nm and 7.76 nm for TSA treated active layers.The
improved morphology of the TSA treated blend is partially
responsible for the better charge transport and collection of
charge carriers, resulting in improved OSC performance.
To gain further insight into the morphological characteristics of the
active layers, we have recorded the transmission electron
microscopy images of the as cast and TSA treated NDIP:PC71BM
thin films. It is well known that the charge transport in the active
layer depends also on the interpenetrating network morphology of
the active layer used in the OSCs. In this case (figure 5), as cast
film exhibits homogeneous morphology between NDIP and
PC71BM which facilitate the exciton dissociation process but
interrupt charge generation and transport. Also, the small domain
size favours the charge recombination.However, the TSA treated
layers showed more finely dispersed phase separation
contributing to better charge transport which suppress the charge
recombination and leads to improved PCE.
(0.015 g, 0.024 mmol), Silverhexafluoroantimonate (0.135 g , 0.04 mmol)
in dichloroethane was stirred for 30 minutes. After this NDI (0.200 g , 0.5
mmol) , N-iodosuccinimide (0.880 g, 0.4 mmol) and Copper acetate
(0.089g, 0.05 mmol) were added and reaction mixture was heated at 80
0C for 48 hours. After the completion of the reaction, reaction mixture was
diluted with dichloromethane and sodium thiosulphate was added. This
was followed water work up. Finally, the reaction mixture was purified by
column chromatography using Chl:Hex as eluent. Compound was further
purified by recrystallization. Yield % = 72 %. 1H NMR (500 MHz, CDCl3) δ
(ppm) 9.24 (s, 2H), 4.97 (m, 2H), 2.13 (m, 2H), 1.90 (m, 2H), 0.82 (m, 12H)
HRMS-APCI Mass: Calc. for C24H24I2 N2O4 (M + nH): 658.9898; found:
658.9889
Synthesis of NDIP:
In
a Schlenk tube, Pd(PPh3)2Cl2 (0.010g, 0.0014 mmoles), CuI
(0.002g, .001 mmoles) , diisopropylamine (5 ml) and dry THF (5 ml) were
added. The mixture was degassed for 20 minutes. This was followed by
the addition of NDI-I2 (0.038 g, 0.006 mmoles) . Degassing was continued
for another 10 minutes. Finally Porp-CH (0.090g, 0.012 mmoles) was
added and the resulting mixture was refluxed overnight under argon. After
the reaction, a small water work up was carried out. Final purification was
done by repetitive columns using silica gel and gel permeation
chromatography. Molecule was recrystallized from hexane/DCM. Yield :
30 % 1H NMR NDIP (500 MHz, CDCl3/PyD5): δ (ppm) = 0.98 (m, 6H),
1.50 (s, 72H), 1.97 (m, 4H), 2.27 (m, 6H), 2.72 (m, 4H), 5.14 (m, 1H), 5.61
(m, 1H), 7.77 (s, 4H), 8.02 (s, 8H), 8.9 (d, J = 4.3 Hz, 2H), 9.1 (d, J = 4.5
Hz, 2H), 9.2 (d, J = 4.3 Hz, 2H), 9.34 ( s, 1H), 10.04 (s, 1H), 10. 3 (d, J =
4.5 Hz, 2H). MALDI-TOF Mass (m/z): Calc. for C124H126N10O4Zn2:
1949.85; found:1949.95. HRMS-APCI Mass (m/z): Calc. for C124H126
N10O4Zn2 (M+nH): 1951.8569; found:1951.8582.
Conclusions
In summary, a novel D--A--D molecular motif containing NDI(A)
as a central core that is connected to porphyrins(D) was
synthesized. The molecule exhibits panchromatic absorption,
which is extended upto NIR, both in solution and thin film. The
energy levels of the molecule align well with those of PCBM.
Consequently, a simple solution processed bulk heterojunction
solar cell was constructed, which after optimization of morphology
afforded a Jsc 15.43 mA/cm2 , Voc 0.83 V, FF of 0.66 and PCE of
8.45%, the highest PCE recorded for any NDI based donors. This
is also the first report in which electron-deficient NDI core is
engineered to be a part of the donor, rather than an acceptor as
reported earlier. with extremely low Eloss of 0.40 eV which is also
the bench mark for NDI based organic solar cells.Therefore, it is
presumed that the current strategy would offer many more
efficient donors for economically viable organic solar cells.
Acknowledgements
The authors sincerely acknowledge CREST-MHRD-FAST and
DST-SERB-EMR/2016/005768, India for the financial support. SS
acknowledges INSPIRE for fellowship. The facilities and
infrastructure provided by IISER Bhopal are highly appreciated.
Keywords: Naphthalenediimide •NIR chromophores• BHJ-Solar
cell • Porphyrins • D--A • organic solar cells
Experimental Section
Synthesis and characterization details for poprhyrin based
precursors are provided in ESI.
[1]
a) L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao, L. Yu. Chem.
Rev. 2015, 115, 12666-12731; b) Y. Lin, X. Zhan. Acc. Chem. Res.
2016, 49, 175-183; c) H. Yao, L. Ye, H. Zhang, S. Li, S. Zhang , J.
Hou. Chem. Rev. 2016, 116, 7397-7457; d) C. Brabec, U. Scherf, V.
Dyakonov, Organic Photovoltaics: Materials, Device Physics, and
Manufacturing Technologies, Wiley-VCH Verlag GmbH & Co. KGaA,
Weinheim, Germany, 2nd edn, 2014.
Synthesis of NDI
A
mixture of Pent-3-ylamine (1.6 ml, 14 mmol), 1,4,5,8-
Naphthalenetetracarboxylic dianhydride (NDA) (2.8g, mmol) in
6
Imidazole (10 g) was stirred at 150 °C . The progress of the reaction was
monitored by TLC. After completion, the reaction mixture was diluted with
ethanol followed by the addition of HCl. The precipitates formed were
collected by vacuum filtration, and purified by repetitive silica gel column
chromatography Chl:Hex) and recrystallization to get desired product of
yield 26 %. 1H NMR (500 MHz, CDCl3) δ (ppm) 8.66 (s, 4H), 4.97 (m, 2H),
2.16 (m, 4H), 1.85 (m, 4H), 0.84 (t, J = 7.5 Hz, 12H). HRMS: Calc. for
C24H26N2O4 (M+nH): 407.1965; found: 407.1968.
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European Journal of Organic Chemistry
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Accepting to Donate: A
small molecular D--A--D
triad NDIP consisting of
naphthalenediimide (NDI)
as an acceptor and
porphyrin as a donor was
synthesized. This molecule
exhibits intense absorption
from visible to NIR region
(400 nm to 1000 nm) and
has high thermal stability.
NDIP turned out to be an
excellent donor in BHJ
solar cell with nearly 8.5%
PCE.
Ruchika Mishra,*[a]Sujesh
S,[b]Archana V. S., [b]
Ayushi Kaushik,[b] Gaurav
Gupta,[c] Rahul Singhal,[d]
Ganesh D Sharma* [c] and
Jeyaraman Sankar*[b
Page No. – Page No.
Title
Naphthalenediimide •NIR
chromophores• BHJ-Solar
cell • Porphyrins • D--A •
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