Role of cyano substituents on thiophene vinylene benzothiadiazole conjugated polymers and application as hole transporting materials in perovskite solar cells

Article abstract of DOI:10.1016/j.jphotochem.2018.11.024

Two narrow-band gap of donor-acceptor based conjugated polymers, BTTP and BTTP-CN were synthesized by Wittig copolymerization with thiophene or cyano-vinylene thiophene as the donor and 2,1,3-benzothiadiazole as acceptor units. The polymers were investigated by FT-IR, UV-V is, fluorescence spectroscopy, thermal stability and cyclic voltammetry (CV). The thermal analysis revealed that the BTTP polymer was stable up to 220 °C and BTTP-CN was stable up to 254 °C. The absorption spectra showed absorption maxima at 403 nm for BTTP and 397 nm for BTTP-CN. The polymers BTTP exhibited orange colour fluorescence emission at 585 nm and BTTP-CN exhibited yellow color fluorescence emission at 520 nm. The optical band gap values of undoped polymers BTTP and BTTP-CN were calculated as 2.2 and 2.13 eV respectively. Novel synthesized polymers were then enforced as dopant/additive-free hole transport materials in perovskite solar cells. Both polymers has shown the photovoltaic performance of 3.80 % for BTTP and 3.48 % for BTTP-CN under 1 sun illumination. The photovoltaic performance are compared with reference hole transporting material of spiro-OMeTAD with and without additive as 12.53 and 7.55% respectively.

Full text of DOI:10.1016/j.jphotochem.2018.11.024

Accepted Manuscript
Title: Role of Cyano Substituents on Thiophene vinylene
benzothiadiazole conjugated polymers and application as hole
transporting materials in perovskite solar cells
Authors: K. Mahesh, S. Karpagam, Thitirat Putnin, Huong Le,
ˆ
Thanh-Tuan Bui, Kontad Ounnunkad, Fabrice Goubard
PII:
S1010-6030(18)30826-8
DOI:
Reference:
https://doi.org/10.1016/j.jphotochem.2018.11.024
JPC 11596
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
12 June 2018
14 November 2018
16 November 2018
ˆ
Please cite this article as: Mahesh K, Karpagam S, Putnin T, Le H, Bui T-Tuan,
Ounnunkad K, Goubard F, Role of Cyano Substituents on Thiophene vinylene
benzothiadiazole conjugated polymers and application as hole transporting materials in
perovskite solar cells, Journal of Photochemistry and amp; Photobiology, A: Chemistry
(2018), https://doi.org/10.1016/j.jphotochem.2018.11.024
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Role of Cyano Substituents on Thiophene vinylene benzothiadiazole
conjugated polymers and application as hole transporting materials in
perovskite solar cells
K. Mahesha, S. Karpagama*,Thitirat Putninb, Huong Le c, Thanh-Tuân Bui c, Kontad
Ounnunkad b, Fabrice Goubardc
aDepartment of Chemistry, School of Advanced Sciences, VIT University, Vellore-14,
TamilNadu, India. *skarpagam80@yahoo.com
b Department of Chemistry and Center of Excellence for Innovation in Chemistry (PERCH-
CIC), Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
c Laboratoire de Physicochimie des Polymères et des Interfaces, Université de Cergy-
Pontoise, 5 mail Gay Lussac, 95031 Neuville-sur-Oise, France
Graphical abstract
Highlights:
 Excellent photoelectronic property of new conjugated polymer contains Thiophene
and benzothiadiazole was synthesized
 Excellent orange and yellow fluorescence, low band gap(1.9, 1.6) and good thermal
stability of the conjugated polymer
 Great potential to act as Hole transporting materials in Perovskite Solar cells.
ABSTRACT

Two narrow-band gap of donor-acceptor based conjugated polymers, BTTP and
BTTP-CN were synthesized by Wittig copolymerization with thiophene or cyano-vinylene
thiophene as the donor and 2,1,3-benzothiadiazole as acceptor units. The polymers were
investigated by FT-IR, UV-Vis, fluorescence spectroscopy, thermal stability and cyclic
voltammetry (CV). The thermal analysis revealed that the BTTP polymer was stable up to
o
o
220 C and BTTP-CN was stable up to 254 C. The absorption spectra showed absorption
maxima at 403 nm for BTTP and 397 nm for BTTP-CN. The polymers BTTP exhibited
orange color fluorescence emission at 585 nm and BTTP-CN exhibited yellow color
fluorescence emission at 520 nm. The optical band gap values of undoped polymers BTTP
and BTTP-CN were calculated as 2.2 and 2.13 eV respectively. Novel synthesized polymers
were then enforced as dopant/additive-free hole transport materials in perovskite solar cells.
Both polymers has shown the photovoltaic performance of 3.80 % for BTTP and 3.48 % for
BTTP-CN under 1 sun illumination. The photovoltaic performance are compared with
reference hole transporting material of spiro-OMeTAD with and without additive as 12.53
and 7.55% respectively.
Keywords: Thiophene; 2,1,3-benzothiadiazole; Perovskite solar cell; low band gap; Hole
transporting materials;
1. Introduction
Conjugated polymers have drawn significant attention from last two decades for
variety of optoelectronic [1] applications such as organic photovoltaic devices (OPVs) [2],
organic field effect transistors (OFETs) [3], organic thin film transistors (OTFTs) [4], and
organic light emitting diodes (OLEDs)[5] due to their tunable optical, electrochemical and
morphological characteristics. In such devices, optoelectronic properties can be explored
through the deposition of semiconducting materials in between of two electrodes.
The most important component is the conjugated backbone in the polymer which can
be regulated by physical properties such as π conjugation length, monomer alteration,
inter/intramolecular interactions and energy levels [6,7]. One of the most capable methods of
lowering the optical and electrochemical band gap of conjugated polymers through the
selection of electron donating (donor) and withdrawing unit (acceptor) in an alternating mode
in the polymer chain [8,9]. Commonly used donor moieties are thiophene [10], fluorene [5],

dithieno[3,2-b:2,3-d]silole [11], carbazole [12], dibenzosilole [8], and cyclopentadithiophene
groups, While acceptors moieties are generally 2,1,3-benzothiadiazole, thieno[3,4-
b]thiophene, dioxypyrrolothiophene and diketopyrrolopyrrole (DPP) [3]. Among the donor
units, thiophene containing conjugated polymers are widespread attention as novel systems
with an excellent hole transporting ability, strong interchain interactions, good light-
harvesting properties, great environmental and thermal stability [14,15]. 2,1,3-
benzothiadiazole (BT) is a good chromophore and strong electron accepting moiety due to
the two electron withdrawing imine groups (-C=N-) which lowers the band gap. And also BT
can be possible to form hydrogen bond with adjacent units because of two N atoms in
thiazole ring, which could give boost to major planar backbone [16].
Organic-Inorganic hybrid solar cells is one of the alternative solar cells and have
attracted to many researchers by trying with new hole transport donor-acceptor materials.
Organic-inorganic hybrid material called as perovskite which is new light absorber which
contain great properties for the development of low-cost thin film solar cells [17]. The
perovskite material performs high absorption coefficient, suitable direct band gap, small
exciton binding energies, high carrier mobilities, long diffusion lengths and superior defect
tolerances [18]. Moreover, perovskite/HTM polymers solar cells have been developed to
achieve high performance. Cai et al showed the PCE upto 18 % for Carbazole and
benzothiadiazole based polymers /perovskite solar cells [19]
The present article deals with the synthesis and characterization of new low band gap
orange and yellow emitting conjugated polymers (BTTP and BTPCN). BTTP was consisted
of repeating units of unsubstituted thiophene and 2,1,3-benzothiadiazole and BTTP-CN was
consisted of repeating units of cyano-vinylene based thiophene 2,1,3-benzothiadiazole.
BTTP-CN has cyano-substituted vinylene linkages which act as strong electron accepting
nature. Due to this nature, it has been extensively adopted in small conjugated molecules
[20]. The CN-group can extremely lower the LUMO level and slightly lower the highest
occupied molecular orbital (HOMO) level; this can prove by Li and co-workers [21]. When
compared to other electron withdrawing moieties, a CN-group containing polymer for
photovoltaic properties has only limited success [22]. Accordingly, more examinations may
be needed to better understand the photovoltaic properties of CN-group containing

conjugated polymers. The vinylene linkages in the conjugated polymer backbone can give
planarity, flexibility and eliminated the torsional strain between donor and acceptor on the
entire conjugated system [23]. Structural characterization was carried out using FT-IR, NMR,
UV-Vis and Cyclic Voltammetry. The potency of these new polymers (BTTP and BTTP-
CN) as hole transport materials (HTM) has been investigated by fabricating
organic/perovskite hybrid solar cells. The photovoltaic performance of these device was
observed and compared with reference HTM materials of spiro-OMeTAD.
2. Experimental section
2.1. Reagents and solvents
Thiophene 2-carbaldehyde, Zn powder, TiCl4, 5-thiophene acetonitrile, potassium
tert-butoxide, POCl3, 4,5-dimethyl-1,2-phenylenediamine, triethylamine, thionyl chloride, N-
bromosuccinimide, benzoyl peroxide, triphenylphosphine, sodium hydride were purchased
from Sigma-Aldrich, Bangalore, India. Solvents such as THF, DMF, DCM, ethyl acetate,
CCl4, and acetonitrile respectively were purchased from Sd-fine chemicals, India. All
solvents were dried and distilled before the synthesis as per standard procedures.
2.2. Characterization methods
FT-IR analysis was studied through Thermo Nicolet 330 FT-IR spectrometer with
KBr pellets with a midrange of (500-4000 cm-1). The 1H and 13C NMR spectra were analyzed
by using a Bruker Advanced III 400 MHz spectrometer using tetramethylsilane (TMS) as an
internal standard. The UV-visible absorption spectra were analyzed on JASCO-V-670 FT-IR
spectrometer. The fluorescence emissions were performed with Perkin-Elmer LS45
fluorescence spectrofluorometer. The lifetime measurements were carried out with Jobin
Yvon FLUOROLOG-FL3-111 spectrofluorometer. The thin films are spin coated onto a
clean glass substrate using apex spin NXG-P1 instrument. A cyclic voltammogram (CV) was
recorded on CH-I 660C instrument. Thermal stability was performed on SDT Q600 V20.9
Build 20 instrument under nitrogen flow rate 100 ml/min. The molecular weights of the
intermediate compounds were measured from Perkin-Elmer Clarus 680 GC-MS spectrometer
and the polymers molecular weight was observed by gel permeation chromatography using a
Waters-RID 2414 instrument.
2.4. Photovoltaic device fabrication:

FTO coated glass substrates were etched with Zn powder and acid solution at the
concentration of 37% HCl and then cleaned the substrate using detergent and ethanol by
sonication. The substrate was then dried by flow gas and exposing to ultraviolet ozone
plasma for 15 min. A precursor solution was prepared by mixing 0.6 mL of titanium
isopropoxide (TTIP), 0.4 mL of acetyl acetone in 7 mL of isopropanol. 20 µL of a precursor
solution of TiO2 layer was spin coated at 2800 rpm, and dried it on hot plate at 125oC for 5
min. The mesoporous TiO2 layer was prepared by diluting the NR30-D paste from Dyesol
with ethanol (1:8 mass ratio). 20 µL of mesoporous TiO2 was spin coated at 2000 rpm, and
dried it again at 125oC for 5 min after that annealed at 540oC for 60 min. The mix solution of
perovskite was prepared at a ratio of 1:1 by mole of PbI2 and CH3NH3I in 71 µL DMSO and
521 µL DMF as solvent. The perovskite layer was spin coated at 4000 rpm1 and dried again
at 100oC for 15 min. A hole transport material were deposited on perovskite layer by spin
coating at 3000 rpm. Finally, the devices were transferred to a thermal–evaporator pump
where a thin gold (100 nm) was deposited. The active area of these devices is 18.04 mm2.
2.4. Synthetic procedure
2.4.1. Preparation of (E)-1,2bis (5-formyl-2-thienyl)ethylene (Donor-1)
Donor-1 was synthesized and purified according to our published procedures [24].
Firstly the compound 2 was prepared from 2-formyl thiophene (1) using TiCl4 and Zinc
powder under nitrogen atmosphere. Then, compound 2 was formylated using DMF and
POCl3 and refluxed for 15 hr. After the product extracted with dichloromethane anResulting
o
brown colour powder was obtained. Yield: 56.25%, mp: 196-198 C. FT-IR: (KBr, ν/cm-1):
1647.25 (-C=O), 1454.4 (C-C stretch in aromatic), 958.65 (trans-vinylene). 1H NMR (CDCl3,
400 MHz, ᵟppm): 7.20 (d, 2 H, thiophene H), 7.62 (d, 2 H, thiophene H), 7.16 (s, 2 H,
vinylene H), 9.80 (s, 2 H, -CHO). 13C NMR (CDCl3, 400 MHz, ᵟppm): 182.62 (-CHO),
150.26, 137.0, 128.28, 142.80 (thiophene C), 124.01 (-CH=CH-). GC-MS calculated for
C12H8O2S2 (m/z) = 248, found, 248.80.
2.4.1. Preparation of 2,3-di-thiophen-2-yl-acrylonitrile (4)
Potassium tert-butoxide (6 g, 53.49 mmol) was added to a stirred solution of 5-thiophene
acetonitrile (3) (5.49 g, 44.58 mmol) which dissolved in ethanol. To this Thiophene 2-
carbaldehyde (1) (5 g, 44.58 mmol) was added dropwise and stirred at room temperature for
2 h. The formed yellow color precipitate was filtered and dried. Yield: 8 g, 83.3%. Mp: 110

oC. FT-IR (KBr, ν/cm-1): 2208.5 (-CN- stretch), 3080.3 (aromatic C-H stretch), 3097.6 (=C-
1
H stretch). H NMR (400 MHz, CDCl3, 훿ppm): 7.61 (d, 1H), 7.53 (d, 1H), 7.49 (s, 1H,
13
cyano-vinylene H), 7.34 (d, 1H), 7.29 (d, 1H), 7.14 (t, 1H), 7.06 (t, 1H). C NMR (100
MHz, CDCl3, 훿ppm): 138.7, 137.5, 132.1, 132.0, 129.9, 128.2, 127.9, 126.9 (8C, thiophene
C) 125.9 (1C, vinylene C), 116.9 (1C, -CN), 103.1 (1C, vinylene C). GC-MS calculated for
C11H7NS2 (m/z) = 217, found, 217.31.
2.4.2. Preparation of 2,3-bis-(5-formyl-thiophene-2-yl)-acrylonitrile (Donor-2)
o
The POCl3 (19.3 ml, 207 mmol) was dropped to DMF (276.1 mmol) at 0 C over a
period of 30 min. Then compound 4 (5 g, 23 mmol) was dissolved in 150 ml of
dichloroethane which was added to above-stirred solution and refluxed for 15 h. After
completion of the reaction, the crude reaction mixture was quenched with 250 mL water and
neutralized to pH 7 by the addition of Na2CO3 solution and extracted with dichloromethane.
Then dichloromethane layer was dried over NaSO4. After solvent evaporation, the crude
product was washed twice with diethyl ether. The resulting brown solid was obtained. Yield:
2 g, 31.8%. Mp: 170 oC. 1H NMR (400 MHz, DMSO-d6, 훿ppm): 9.98 (s, 1H, -CHO), 9.89 (s,
1H, -CHO), 8.34 (s, 1H, cyano-vinylene H), 8.01 (d, 1H), 7.82 (d, 1H), 7.54 (d, 1H), 7.28 (d,
1H). 13C NMR (100 MHz, DMSO-d6, 훿ppm): 184.7, 184.1 (2C, -CHO), 146.7, 142.4, 138.6,
137.1, 136.7, 136.4, 133.6, 128.4 (8C, thiophene C), 126.9 (1C, vinylene C), 116.4 (1C, -
CN), 99.9 (1C, vinylene C). HRMS calculated for C13H7NO2S2 (m/z) = 273 found, 272.9920.
2.4.3. Preparation of 5,6-Dimethyl-[2,1,3] benzothiadiazole (6 )
4,5-dimethyl-1,2-phenylenediamine (5) (5 g, 36.71 mmol) and triethylamine (18.57 g,
o
183.55) were dissolved in CH2Cl2 (150 mL) and cooled to 0 C. Thionyl chloride (8.73 g,
73.42 mmol) was slowly dropped to the stirred solution and refluxed for 6 h. After
completion of the reaction, the crude mixture was diluted with 300 mL water and extracted
with dichloromethane. The organic phase dried over anhydrous Na2SO4. The crude product
was purified by using column chromatography on silica gel (1:9 ethyl acetate/hexane as
mobile phase). The compound 6 was observed as colorless solid. Yield: 4 g, 66.44%. Mp: 72
oC. 1H NMR (400 MHz, CDCl3, 훿ppm): 7.71 (s, 2H, benothiadiazole H), 2.42 (s, 6H, -CH3-).
13C NMR (100 MHz, CDCl3, 훿ppm): 154.27, 140.53, 119.77 (6C, benothiadiazole C), 20.79
(2C, -CH3-). GC-MS calculated for C8H8N2S (m/z) = 164, found, 164.80.

2.4.4. Preparation of 5,6-bis(bromomethyl)[2,1,3] benzothiadiazole (7)
Compound 6 (4 g, 24.35 mmol), N-bromosuccinimide (NBS) (8.66 g, 48.71 mmol), and
benzoyl peroxide (0.23 g, 0.97 mmol) were dissolved in CCl4 (100 mL) and refluxed for 6 h.
The reaction mixture was cooled and succinimide salt was removed by filtration and the
filtrate was evaporated. The compound 7 was observed in the brown color solid. Yield: 6.5 g,
83.4%. Mp: 80 oC. 1H NMR (400 MHz, CDCl3, 훿ppm): 8.06 (s, 2H, benothiadiazole H), 4.84
(s, 4H, -CH2-). 13C NMR (100 MHz, CDCl3, 훿ppm): 154.52, 138.24, 123.55 (6C,
benothiadiazole C), 30.08 (2C, -CH2-). GC-MS calculated for C8H6Br2N2S (m/z) = 319,
found, 319.86.
2.4.5. Preparation of 5,6-bis(triphenylphosphonium di bromomethyl)[2,1,3] benzothiadiazole
(Acceptor-1 )
Compound 7 (2 g, 6.25 mmol), and triphenylphosphine (3.44 g, 13.13 mmol) were
dissolved in 1:9 ratio of CH3CN (100 mL) and CH2Cl2 (10 mL). The resulting suspension was
stirred at room temperature for overnight. The formation of a colorless precipitate was
filtered and washed twice with diethyl ether. Yield: 4.24, 80%. FT-IR (KBr, ν/cm-1): 3053.3
(aromatic C-H stretch), 1739.7 (C=C bending), 1435.0 (aromatic C-C stretch), 1585.4 (C=N
1
stretch), 742.59 (C-P), 686.6 (C-Br). H NMR (400 MHz, DMSO-d6, 훿ppm): 7.94-7.57 (m,
1
32H, phenyl H), 4.75 (s, 4H, -CH2-). 13C NMR (100 MHz, DMSO-d6, 훿ppm): 152.64,
135.39, 134.07, 133.97, 130.32, 130.20, 129.36, 125.1, 117.53, 116.6 (aromatic C), 30.6 (2C,
-CH2-). HRMS calculated for C44H36Br2N2P2S (m/z) = 844 found, 844.0438.
2.4.6. General procedure for the synthesis of polymers
Acceptor-1 (2.1 g, 2.48 mmol) was dissolved in 100 mL of anhydrous THF. To this
60% sodium hydride (3.96 g, 99.22 mmol) was added as portion wise, and the color of
reaction mixture was changed from colorless to a purple color. After donor-1 or 2 (1.23 g,
4.96 mmol) was added portion wise to the reaction mixture and reflux for overnight. The
reaction mixture was cooled to room temperature, diluted with ice cold water and extracted
with ethyl acetate. After solvent evaporation, the crude product was recrystallized from
isopropanol.
BTTP: Red color solid, FT-IR (KBr, ν/cm-1): 3012 (aromatic C-H stretch), 1656 (-C=C-
1
stretch in conjugation), 1531 (aromatic C=C stretch), 931 (trans-vinylene) H NMR (400

MHz, DMSO-d6, 훿ppm): 7.65-7.59 (br, thiophene H), 7.59-7.57 (br, benzothiadiazole H),
7.57-7.50 (br, vinylene H).
BTTP-CN: Brown colour solid, FT-IR (KBr, ν/cm-1): 3018 (aromatic C-H stretch), 2210 (-
1
CN group), 1739 (C=C-CN stretch), 1587 (aromatic C=C stretch). H NMR (400 MHz,
DMSO-d6, 훿ppm): 7.64-7.59 (br, thiophene H), 7.59-7.57 (br, benzothiadiazole H), 7.57-7.51
(br, vinylene H).
3. Results and Discussion
3.1. Synthesis and characterization of monomers and polymers
The general synthetic strategy for the establishing monomers and two polymers are
outlined in the scheme. 1. The structures of both monomers and target polymers were
confirmed by FT-IR and 1H NMR spectroscopic techniques. Firstly, the thiophene donor type
of intermediate (2) was synthesized from commercially available 2-thiophene
carboxaldehyde (1) using Zn powder, TiCl4 via McMurry coupling reaction as follows to that
reported literature [24]. Newly formed vinyl linkage signal appeared at 7.0 ppm (J =14) in 1H
NMR which indicates the intermediate (2) was in trans-configuration. The cyano containing
intermediate (4) was synthesized from compound (1) and 2-thiopheneacetonitrile (3) using t-
BuOK as a base. Resulting cyano-vinylene bond was confirmed by appearing the sharp
absorption band at 2208.5 in FT-IR. The Donors and acceptor were synthesized from
intermediates (2 & 4) by well-known Vilsmeier-Haack reaction. Both monomers contain
aldehyde functional groups were observed at 1647.20, 1645.28 cm-1 in FT-IR, aldehyde
protons, and carbon signals appeared at 9.80, 9.89, 9.98 and 182, 184.1, 184.7 ppm in 1H and
C13 NMR spectrum. These values were confirmed for the formation of formyl thiophene
group (Donor-1 and 2).
Secondly, in the part of acceptor side, Dimethyl benzothiadiazole (6) was synthesized
from reported literature [25]. Bromomethyl 2,1,3-Benzothiadiazole was firstly synthesized
using N-bromosuccinimide (NBS) reagent and benzoyl peroxide as an initiator. This was
1
confirmed by appearance of -CH2-Br signal at 4.84 ppm in H NMR, and then directly
converted to monomer (M3) by treatment with triphenylphosphine. The structure of M3 was
confirmed by appearing the sharp absorption bands at 742.59 (C-P stretching), 686.66 (C-Br
1
stretching) in FT-IR and 7.94-7.57 ppm (32 phenyl hydrogens of phosphonium salt) in H
NMR spectra.

Synthesis of donor moieties:
Synthesis of acceptor moiety:
Synthesis of polymers:
Scheme 1: Synthetic reaction of donors, acceptors and polymers

3.2. Structural Characterization of the polymers (BTTP and BTTP-CN)
The synthetic procedures of both polymers (BTTP, BTTP-CN) are sketched in
Scheme 1. Both polymers were synthesized from the thiophene dicarbaldehyde monomers
(Donor-1 &2) and benzothiadiazole phosphonium salt monomer (Acceptor) in dry THF
solvent using popular Wittig condensation reaction followed by Sodium hydride as a base for
deprotonation of phosphonium salt. The structural characteristics of both polymers were
verified from FTIR and NMR spectroscopy.
BTTP and BTTP-CN are interesting conjugated conductive polymers containing an
electron pair donating nitrogen atoms. The polymers was investigated by FT-IR spectra
which are shown in Fig. 1. Both polymers (BTTP, BTTP-CN) were showed characteristic
absorption band at 3012.8, 3018.6 cm-1 which indicated for thiophene C-H stretching, 1656,
1730 cm-1 was represented for -C=N- stretching in benzothiadiazole, 1531.4, 1587 cm-1 was
represented for -C=C- stretching. In BTTP-CN, the medium absorption peak at 2220 cm-1
was represented for the –CN group. The absorption at 931, 939 cm-1 was denoted that trans-
vinylene was predominant among newly formed vinylene double bonds. These values are
suggested for the successful reaction of donors with acceptor.
Fig. 1. FT-IR spectra of the polymers
1
Both H NMR spectra of the polymers are shown in Fig. 2. All thiophene protons of
both polymers were shown broad peak signal in between of 7.64-7.59 ppm. The benzene
protons signal of the benzothiadiazole group was formed at 7.59-7.57 ppm. The broad signal
formed at 7.57-7.50 due to vinylene protons. Both polymers were exhibited good solubility in
THF, chloroform, and limited solubility in halo substituted benzenes at room temperature.
Complete solubility could be achieved by elevated temperatures.

Fig. 2. 1H NMR spectra of both polymers.
The number average (Mn), weight average molecular weight (Mw) and polydispersity
index (PDI) were measured by gel permeation chromatography (GPC) against polystyrene
standards using THF as eluent. BTTP has received higher molecular weight (Mn) as 20553 Da
with PDI of 1.41 and for BTTP-CN has been found Mn was 9526 Da with PDI of 1.21
3.5. Optical properties
3.5.1. Absorption spectra
The optical related properties of both polymers were explored by UV-vis absorption
spectroscopy. The absorption spectra of the both polymers were measured in chloroform
solvent (5×10-5 M) and thin films which are shown in Fig. 3 and the values indicated in Table
1. The absorption peaks of both polymers were appeared at short (high energy band)
wavelength because of π-π* transition and long wavelength (low energy band, n-π*) regions
because of internal charge transfer (ICT) [26]. This is the common feature in conjugated
polymers due to donor-acceptor orbital hybridization [27]. In solution, BTTP polymer was
shown absorption peak at 266 nm and BTTP-CN polymer shown absorption at 317 nm which
due to the π-π* transition band. BTTP showed broad absorption peak in the range of 320-550
nm with 403 nm of absorption maxima and BTTP-CN showed absorption peak at 397 nm
related to n-π* transition. Based upon these results unsubstituted vinylene link polymer
(BTTP) was shown 10 nm of bathochromic shift than cyano substituted vinylene polymer
(BTTP-CN). In thin films, both copolymers were displayed similar broadening of absorption
peaks and maxima. BTTP and BTTP-CN exhibited a bathochromic shift in thin film
absorption onset (560 nm and 580 nm). It could be due to solid state effect and aggregation π-

π stacking occurred between polymer chains [28]. The band edge of the polymer (BTTP) thin
film was observed at 560 nm and the corresponding optical band gap was 2.2 eV. But, in the
case of cyano substituent polymer possess the band edge was 580 nm and the corresponding
optical band gap was 2.13 eV. Lesser band gap in the solid state of the polymer enhance
intramolecular charge transfer between thiophene donor and thiazole acceptors.
Fig. 3 (a) Absorption spectra of the polymers in CHCl3 and thin film state (b)Visual
change photos of both polymers under daylight
Figure 4 shows diffuse reflectance (DR) spectra of powdery polymers of BTTP and BTTP-
CN. Broader DR spectra was able to observe for both polymers (BTTP and BTTP-CN) and
observed in the range of 350-500 nm. The absorption band of the BTTP and BTTP-CN were
396 and 392 nm which seems to be shifted to longer wavelengths compared to solution state
of the polymers. These polymers were exhibited the peaks at different position from those
observed with the solution and thin film state which suggest a strong intermolecular
electronic interaction between donor and acceptor moieties.

Fig. 4. Diffuse reflectance (DR) spectra of the polymers
3.5.2. Fluorescence spectra
Fig. 5 depicts the fluorescent emission spectra of both polymers in chloroform and
spin coated films. In a solution state, the polymer without cyano group (BTTP) showed
strong orange fluorescent colour with emission maxima at 585 nm and with cyano polymer
(BTTP-CN) exhibited yellowish fluorescent colour with emission maxima at 520 nm. The
emission spectra of the polymers in film state is much broadened than the emission from thin
films. The excitation spectrum of the both polymers for the emission wavelength gives the
information about π-π* transitions results in more intense fluorescence emission. The
emission maximum of the polymers is blushifted compared to solid state of the polymer
which was noticed at 580 nm and 650 nm for BTTP-CN and BTTP polymers. Fluorescence
emission of cyano substituent polymer is strongly blue shifted than polymer without cyano.
This may be caused by the strong intramolecular charge transfer (ICT) between thiophene
and benzthiadiazole group. ICT is much stronger in cyano containing polymers because of
dicyanovinyl group is much stronger electron acceptor. [29]

(b)
(a)
Fig. 5 (a) Fluorescence spectra of the polymers in CHCl3 and thin film state (b)
Visual change photos of both polymers under UV light
The wave length gap between the absorption maxima and fluorescence maxima is
called the Stokes shift. The luminescence property is depending upon the Stokes shift value.
The decreased luminescence of polymers is due to lower stokes shift, because of self-
absorbing the emitted light. The Stokes shift was determined according to the given formula.
∆λStokes = λmax. emission - λmax. absorption
(1)
Stokes shift of BTTP and BTTP-CN was calculated as 182 nm and 123 nm. Both
polymers were exhibited higher Stokes shift values than previously published thiophene-
thiazole based oligomers [25]. The large Stokes shift is in favor of practical applications since
it can decrease self-quenching and increase the luminescence [30]. From the optical
properties of both polymers, it is noticeable that the interaction between donor and acceptor
backbone greatly depends on several aspects such as attachment of donor-acceptor, their
strength, steric hindrance and planarity of the polymer backbone.

Table. 1 Comparative spectral analysis of both polymers (BTTP and BTTP-CN).
Measurement
Absorption
spectra
Properties
Absorption maxima (nm) 266 ,403
UV-Onset absorption
Optical Band gap (eV)
Emission maxima (nm)
BTTP
BTTP-CN
317,397
580
2.13
520
123
0.85
-0.75
-5.25
-3.65
1.60
560
2.2
585
182
1.00
-0.90
-5.40
-3.50
1.90
Fluorescence
Spectra
Electrochemical 퐸
Stokes Shift (nm)
표푥
(V)
(V)
표푛푠푒푡
푟푒푑
(CV)
퐸
표푛푠푒푡
HOMO (eV)
LUMO (eV)
퐸푔퐸푐 (eV)
Analysis
Bi-exponential
Bi-exponential
Fluorescence
Life time
Lifetime (ns)
τ1 =1.05
τ2 = 2.18
τ3 = Nil
A1 =49.87
A2 =50.13
1.26
τ1 =0.72
τ2 = 3.06
τ3 = Nil
A1 =67.60
A2 =32.40
1.67
Amplitude
χ2
3.5.3. Fluorescence lifetime measurement
Fluorescence lifetime was evaluated to find the time of the present polymer spends
time in the excited state before coming to the ground state. Fig. 6 shows typical fluorescence
lifetime (decay time) spectra of the polymers BTTP and BTTP-CN with the emission
wavelengths of 585 and 520 nm. Both polymers of nanosecond time profiles were calculated
by utilizing a time-correlated single photon counting method [31]. Exploration of the
polymers decay curves confirmed that it could be fitted completely with that two exponential
decay function of the form (2) and tri-exponential decay function of the form (3).
−푡
−푡
휏
휏
2
1
( )
퐹 푡 = 퐴1푒 + 퐴2푒
(2)
(3)
−푡
−푡
−푡
휏
3
휏
1
휏
2
( )
퐹 푡 = 퐴1푒 + 퐴2푒 + 퐴3푒
Where ‘A’ is the amplitude of fluorescence intensity at time zero and ‘τ’ is
fluorescence lifetime. Bi-exponential curves was calculated from the parameters for BTTP
and BTTP-CN which are displayed in Table 1. The assertive first lifetime (τ1) of BTTP is
1.05 ns and a second lifetime τ2 = 2.18 ns have the lowest χ2 fit (1.26). The reduced first
lifetime (τ2) for BTTP-CN is 0.72 ns and a second lifetime τ2 = 3.06 ns have the 1.67 χ2 fit.

The nature of the fit was determined by the examination of the residuals, and the value of the
lower χ2 ratio [31].
Fig. 6. Fluorescence Lifetime spectrum of the polymers BTTP and BTTP-CN
3.6. Electrochemical measurements
The electrochemical properties of both copolymers were investigated by cyclic
voltammetry. By utilizing this technique HOMO and LUMO energy levels of polymers can
be determined. These energy levels are necessary for calculating the electrochemical band
gap of the polymers. The cyclic voltammetry studies were carried out in a 0.1 mol/L
tetrabutylammonium hexafluorophosphate (Bu4NPF6) solution in CH3CN at ambient
temperature using 50 mV/s scan rate under room temperature. An ITO plate used as a
working electrode. It is coated with the polymer thin film by drop casting method. The
Bu4NPF6 used as a supporting electrolyte, Ag/AgCl as a reference electrode and platinum
ec
wire used as a counter electrode. The HOMO, LUMO and electrochemical band gap (Eg )
value of both polymers were estimated using the reported empirical equation [32].
EHOMO = -(Eox+ 4.4)
ELUMO = -(Ered+ 4.4)
Eg= EHOMO -ELUMO.
(4.1)
(4.2)
(4.3)
Fig. 7 shows the cyclic voltammograms of BTTP and BTTP-CN polymers. Clearly,
both polymers have positive (oxidation) and negative (reduction) peaks which indicate the
great combination of donor and acceptor units in the system. While introducing the electron-
withdrawing elements such as cyano group at vinyl position of electron accepting block can

tune the HOMO and LUMO energy levels of the polymers resulted lower band gap. The
onset oxidation (Eox) and reduction (Ered) potentials of BTTP were 1.0 and -0.9 V
respectively. The HOMO and LUMO energy levels were -5.40 and -3.50 eV respectively and
electrochemical energy band gap was 1.9 eV. The onset oxidation (Eox) and reduction (Ered)
potentials of BTTP-CN were 0.85 V and -0.75 V respectively. The HOMO and LUMO
energy levels of BTTP-CN were -5.25 and -3.65 eV with electrochemical energy band gap
was 1.6 eV. The cyano substituted polymer (BTTP-CN) showed significantly reduced
LUMO energy level compared with polymer (BTTP). The HOMO energy levels of the new
polymers were mainly related to the donor moiety but could also be affected by acceptor
moiety. BTTP-CN displayed slightly increased HOMO energy levels compared with BTTP
polymer. Because of lower electrochemical band gap, these polymers could be employed in
solar cell applications.
Fig. 7. Cyclic voltammograms of the polymers (BTTP and BTTP-CN) sample thin films
on ITO glass in 0.1 M Bu4NPF6 of CH3CN solution with a scan rate of 50 mV/s.
3.7. Thermal analysis
Thermogravimetric analysis (TGA) is important and useful dynamic way to
distinguish the degradation nature of the polymers. Thermal stability or degradation for the
conjugated polymers is essential characterization for their potential applications. The thermal
stability of both polymers is displayed in Fig. 8. Two stages of thermal decomposition were
exhibited by both polymers. For BTTP, the first thermal decomposition temperature with
o
o
10% weight loss at 220 C. The second stage of thermal decomposition began at 325 C and

continued up to 800 oC with 75% weight loss. For BTTP-CN, the first thermal decomposition
o
temperature with 10% weight loss at 254 C. The second stage of thermal decomposition
o
o
began at 325 C and continued up to 800 C with 90% weight loss. Among these two
polymers, BTTP-CN has high thermal stability due to a cyano group, because the strong
electron withdrawing nature of cyano group can increase the stabilization of the frontier
molecular orbitals for semiconducting polymeric materials. Furthermore, it extended a strong
intermolecular interaction [33, 34]. Definitely, the thermal stability of both polymers is
capable for their applications in optoelectronic devices.
Fig. 8. TGA curve of BTTP and BTTP-CN at a heating rate of 10 oC min-1 under nitrogen.
3.9. Photovoltaic properties
We have also investigated the potentiality of these thiophene and benzothiadiazole
based conjugated polymers (BTTP and BTTP-CN) as hole transporting materials (HTM) in
hybrid perovskite solar cells (PSC). The general device structure is given in Fig. 9 (left). The
PSC is composed of an FTO/glass substrate covered successively by a thin compact c-TiO2
(50 nm thickness) and then a mesoporous mp-TiO2 layers (200 nm thickness). The solution
containing CH3NH3I + PbI2 is then spin coated on the glass/c-TiO2/mp-TiO2 film, followed
by a thermal annealing to form the perovskite absorbing layer (400 nm thickness). Finally,
hole transport layer is spin coated (200n nm thickness) and a thin layer of Au was deposed by
thermal evaporation to serve as cathode. The energy level alignment of different device
components used in our study is displayed in Fig. 9 (right). The Spiro-OMeTAD (2,2',7,7'-

Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene) without additive is used as
control material and its HOMO/LUMO characteristics are taken from our previous reported
results [35].
Fig. 9. General solar cell device structure (left) and energy level alignment of different
device components (right).
As shown in Fig. 9, the HOMO levels of BTTP and BTTP-CN are a little bit higher
than that of the CH3NH3PbI3 perovskite material, suggesting that hole charge are able to be
transferred from perovskite to the two polymers at their interfaces. In other hand, their
LUMO energy levels are located higher than that of perovskite, suggesting that BTTP and
BTTP-CN could have electron-blocking property. But reasonably, HOMO energy
differences is not so big and we cannot exclude a non-negligible recombination state at
HTM/perovskite.
The perovskite-based solar cells were elaborated using BTTP, BTTP-CN, and
Spiro-OMeTAD as hole-transporting materials. It is well known that pristine organic
semiconducting materials have low conductivity and hole mobility, leading to poor
perovskite solar cell performance. The most popular HTM dopants are
bis(trifluoromethane)sulfoimide (LiTFSI) and tert-butylpyridine (tBP). The latter increases
the mobility of the charge carriers [36] and the former increases the carrier density [37].
However, both contribute also largely to the degradation of the stability of perovskite
material [38,39]. For this reason, developing HTM working without any additive is a
promising approach to enhance the long-term stability of the PSC device.

The J-V curves of the best devices are shown in Fig. 10 and the photovoltaic outputs
are tabulated in the Table 2. The control device using doped Spiro-OMeTAD HTM gave a
photocurrent density (Jsc) of 21.93 mA.cm-2, fill factor (FF) of 0.62 and an open circuit
voltage (Voc) of 0.92 V, corresponding to the power conversion efficiency (PCE) of 12.53 %.
The device using pristine Spiro-OMeTAD without any additive gave poorer photovoltaic
performance (7.55 %), mostly due to lower photocurrent. This demonstrates the effects of
additive in increasing the performance of PSC as reported in our previous work [40]. Herein
the photovoltaic performance of Spiro-OMeTAD based device validated our device
elaboration procedure.
Fig. 10. J-V curves of the devices based on FTO/bl-TiO2/m-TiO2/MAPbI3/HTM/Au
device structure under illumination and in the dark: BTTP (red) and BTTP-CN (blue).
Table 2. Photovoltaic parameters derived from J-V measurements
JSC
VOC
(V)
PCE
(%)
Devices
FF
(mA/cm2)
Spiro-MeOTAD
21.93
0.920
0.620
12.53
Spiro-MeOTAD w/o additive
BTTP in Chloroform
12.69
10.11
0.880
0.780
0.676
0.482
7.55
3.80

BTTP-CN in Chloroform
10.01
0.690
0.503
3.48
The BTTP based device delivered a Jsc of 10.11 mA∙cm-2, a Voc of 0.78 V, and an FF
of 0.48, corresponding to a PCE of 3.80 %. BTTP-CN exhibited a Jsc of 10.01, a Voc of 0.69
V and an FF of 0.50 leading to a PCE of 3.5 %. Despite a better FF compared to that of
BTTP, BTTP-CN photovoltaic performance is poorer than that of BTTP due to lower Jsc
and Voc. Although more effort should be made to understand the role of thiophene and
benzothiadiazole based conjugated polymers BTTP and BTTP-CN HTM layer in the PSC
photovoltaic performance, we thus attributed this difference in photovoltaic performance to
both low charge carrier mobility of pristine BTTP and BTTP-CN and certainly a non-
negligible recombination ratio at HTM/perovskite interface which causes directly the low
photocurrents observed. Moreover, chloroform used as the most efficient HTM solvent is not
the most adequate for high efficient PSC elaboration. However, these preliminary results
show the potentiality of solution processable BTTP and BTTP-CN as HTM for hybrid
photovoltaics.
4. Conclusion
In summary, thiophene and benzothiadiazole based conjugated polymers (BTTP, BTTP-CN)
with and without cyano group has been synthesized with several schematic steps. The
Donors, acceptors and Polymers were characterized using FTIR, NMR, Mass and GPC
technique. These polymers are soluble in common organic solvents such as THF and CHCl3
which allows to use as thin films in the elaboration of electronic devices. BTTP has emitted
strong orange colour and cyano substituted BTTP emitted yellowish colour with maxima of
520 nm. Cyano substituent has placed very important role in the conjugated polymers
(BTTP) to reduced band gap (1.6 eV), fluorescence life time (0.72 ns), higher thermal
stability (325 οC), increased HOMO level (-5.25eV), decreased LUMO level (-3.65). Overall,
both polymers have numerous potential applications in the field of photovoltaics, OLEDs,
and nonlinear optics. Ability of new polymers as hole transporting materials in perovskite
solar cells has been analyzed. BTTP has shown better photovoltaic performance (PCE: 3.8
%) than BTTP-CN and this was very less compared to Spiro-OMeTAD based device. In
future, these polymers maybe doped with various Lewis acid to increase conductivity and
able to improve the photovoltaic performance of perovskite solar cells.

Acknowledgement
This work was financially supported by DST-SERB, New Delhi (Grant no.
SB/FT/CS-140/2013). The authors are grateful to DST/VIT-FIST, VIT University for
providing instrumental facilities.
References
[1] D.H. Yun, H.S. Yoo, S.W. Heo, H.J. Song, D.K. Moon, J.W. Woo, Y.S. Park, Synthesis
and photovoltaic characterization of D/A structure compound based on N-substituted
phenothiazine and benzothiadiazole, J. Ind. Eng. Chem. 19 (2013) 421-426.
[2] S. Goker, G. Hizalan, E. Aktas, S. Kutkan, A. Cirpan, L. Toppare, 2, 1, 3-
Benzooxadiazole, thiophene and benzodithiophene based random copolymers for organic
photovoltaics: thiophene versus thieno [3, 2-b] thiophene as π-conjugated linkers, New J.
Chem. 40 (2016) 10455-10464.
[3] J. Yuan, X. Huang, F. Zhang, J. Lu, Z. Zhai, C. Di, W. Ma, Design of benzodithiophene-
diketopyrrolopyrrole based donor–acceptor copolymers for efficient organic field effect
transistors and polymer solar cells, J. Mater. Chem. 22 (2012) 22734-22742.
[4] M.C. Hwang, J.W. Jang, T.K. An, C.E. Park, Y.H. Kim, S.K. Kwon, Synthesis and
characterization of new thermally stable poly (naphthodithiophene) derivatives and
applications for high-performance organic thin film transistors, Macromolecules. 45 (2012)
4520-4528.
[5] H. Shi, J. Yuan, X. Wu, X. Dong, L. Fang, Y. Miao, F. Cheng, H. Shi, J. Yuan, X. Wu,
X. Dong, L. Fang, Y. Miao, F. Cheng, Two novel indolo [3, 2-b] carbazole derivatives
containing dimesitylboron moieties: synthesis, photoluminescent and electroluminescent
properties, New J. Chem. 38 (2014) 2368-2378.
[6] D. Dang, M. Xiao, P. Zhou, J. Shi, Q. Tao, H. Tan, R. Yang, Manipulating backbone
structure with various conjugated spacers to enhance photovoltaic performance of D–A-type
two-dimensional copolymers, Org. Electron. 15 (2014) 2876-2884.
[7] G. Zuo, Z. Li, M. Zhang, X. Guo, Y. Wu, S. Zhang, Influence of the backbone
conformation of conjugated polymers on morphology and photovoltaic properties, J. Hou,
Polym. Chem. 5 (2014) 1976-1981.
[8]
H.J. Song, J.Y. Lee, E.J. Lee, D.K. Moon, Conjugated polymer consisting of
dibenzosilole and quinoxaline as donor materials for organic photovoltaics, Eur. Polym. J. 49
(2013) 3261-3270.
[9] M.L. Keshtov, D.V. Marochkin, V.S. Kochurov, A.R. Khokhlov, E.N. Koukaras, G.D.
Sharma, New conjugated alternating benzodithiophene-containing copolymers with different
acceptor units: synthesis and photovoltaic application, J. Mater. Chem. A. 2 (2014) 155-171.

[10] B. Zaifoglu, M. Sendur, N.A. Unlu, L. Toppare, High optical transparency in all redox
states: Synthesis and characterization of benzimidazole and thieno [3, 2-b] thiophene
containing conjugated polymers, Electrochim. Acta. 85 (2012) 78-83.
[11] J.H. Kim, K.H. Kim, J. Shin, T.W. Lee, M.J. Cho, D.H. Choi, Electrical and
photoelectrical properties of polymer single nanowire made of diketopyrrolopyrrole-based
conjugated copolymer bearing dithieno [3, 2-b: 2′, 3′-d] thiophene, Synth. Met. 167 (2013)
37-42.
[12] A. Upadhyay, S. Karpagam, Synthesis and photo physical properties of carbazole based
quinoxaline conjugated polymer for fluorescent detection of Ni2+, Dyes. Pigments. 139
(2017) 50-64.
[13] T. Ikai, R. Kojima, S. Katori, T. Yamamoto, T. Kuwabara, K. Maeda, S. Kanoh, Thieno
[3, 4-b] thiophene–benzo [1, 2-b: 4, 5-b′] dithiophene-based polymers bearing optically pure
2-ethylhexyl pendants: Synthesis and application in polymer solar cells, Polymer. 56 (2015)
171-177.
[14] Y. Zou, A. Najari, P. Berrouard, S. Beaupre, B. Reda Aich, Y. Tao, M. Leclerc, A thieno
[3, 4-c] pyrrole-4, 6-dione-based copolymer for efficient solar cells, J.Am. Chem. Soc. 132
(2010) 5330-5331.
[15] L. Huo, J. Hou, S. Zhang, H.Y. Chen, Y. Yang, A Polybenzo [1, 2‐b: 4, 5‐b′]
dithiophene Derivative with Deep HOMO Level and Its Application in High‐Performance
Polymer Solar Cells, Angew. Chem. Int. Ed. 49 (2010) 1500-1503.
[16] X. Huang, G. Zhang, C. Zhou, S. Liu, J. Zhang, L. Ying, Y. Cao, Tailoring π-
conjugated dithienosilole–benzothiadiazole oligomers for organic solar cells, New J. Chem.
39 (2015) 3658-3664.
[17]. M.I. Ahmed, A. Habib, S.S. Javaid. Perovskite solar cells: potentials, challenges, and
opportunities. Int J Photo energy (2015) 2015:592308.
[18]. Z. Liu, Q. Chen, Z. Hong, H. Zhou, X. Xu, N. De Marco, P. Sun, Z. Zhao, Y.B. Cheng,
Y. Yang, Low-temperature TiOx compact layer for planar heterojunction perovskite solar
cells. ACS Appl Mater Interfaces 8 (2016) 11076–83.
[19] F.Cai, J. Cai, L. Yang, W. Li, R.S. Gurney, H. Yi, A. Iraqi, D. Liu, T. Wang, Molecular
engineering of conjugated polymers for efficient hole transport and defect passivation in
perovskite solar cells, Nano Energy,45 (2018)28-36.
[20] Y. Lin, Z.G. Zhang, H. Bai, Y. Li, X. Zhan, A star-shaped oligothiophene end-capped
with alkyl cyanoacetate groups for solution-processed organic solar cells, Chem. Commun.
48 (2012) 9655-9657.
[21] S. Zeng, L. Yin, C. Ji, X. Jiang, K. Li, Y. Li, Y. Wang, D–π–A–π–D type
benzothiadiazole–triphenylamine based small molecules containing cyano on the π-bridge for
solution-processed organic solar cells with high open-circuit voltage, Chem. Commun. 48
(2012) 10627-10629.

[22] Z. Tan, I. Imae, K. Komaguchi, Y. Ooyama, J. Ohshita and Y. Harima, Effects of π-
conjugated side chains on properties and performances of photovoltaic copolymers, Synth.
Met. 187 (2014) 30-36.
[23] A. Casey, Y. Han, Z. Fei, A.J. White, T.D. Anthopoulos, M. Heeney, Cyano substituted
benzothiadiazole: a novel acceptor inducing n-type behaviour in conjugated polymers, J.
Mater. Chem. C. 3 (2015) 265-275.
[24] K. Mahesh, S. Karpagam, Synthesis and optoelectronic properties of thiophene donor
and thiazole acceptor based blue fluorescent conjugated oligomers, J. Fluoresce. 26 (2016)
1457-1466.
[25] Z.F. Shi, H.T. Black, A. Dadvand, D.F. Perepichka, Pentacenobis (thiadiazole) dione,
an n-Type Semiconductor for Field-Effect Transistors, J. Org. Chem.79 (2014) 5858-5860.
[26] P. Leriche, P. Frere, A. Cravino, O. Alévêque, J. Roncali, Molecular engineering of the
internal charge transfer in thiophene− triphenylamine hybrid π-conjugated systems, J. Org.
Chem. 72 (2007) 8332-8336.
[27] P. Sonar, E.L. Williams, S.P. Singh, A. Dodabalapur, Thiophene–benzothiadiazole–
thiophene (D–A–D) based polymers: effect of donor/acceptor moieties adjacent to D–A–D
segment on photophysical and photovoltaic properties, J. Mater. Chem. 21 (2011) 10532-
10541.
[28] Z.G. Zhang, Y. Yang, S. Zhang, J. Min, J. Zhang, M. Zhang, Y. Li, Effect of acceptor
substituents on photophysical and photovoltaic properties of triphenylamine–carbazole
alternating copolymers, Synth.Met. 161 (2011) 1383-1389.
[29] M.S. Liu, X. Jiang, S.Liu, P. Herguth, A.K-Y. Jen, Effect of cyano substitutents on
electron affinity and electron transporting properties of conjugated polymers,
Macromolecules, 35 (2002) 3532-3538.
[30] Z. Gao, Y. Hao, M. Zheng, Y. Chen, A fluorescent dye with large Stokes shift and high
stability: synthesis and application to live cell imaging, RSC Adv. 7 (2017) 7604-7609.
[31] S. Selvakumar, K. Sivaji, A.A. Chakkaravarthi, S. Sankar, Enhanced fluorescence and
time resolved fluorescence properties of p-terphenyl crystal grown by selective self seeded
vertical Bridgman technique, Mater. Let. 61 (2007) 4718-21.
[32] H. Qin, L. Li, Y. Li, X. Peng, J. Peng, Y. Cao, W. Shi, Enhancing the performance of a
thieno [3-4-b] pyrazine based polymer solar cell by introducing ethynylene linkages, Eur.
Polym. J. 48 (2012) 2076-2084.
[33] X. Zhao, X. Zhan, Electron transporting semiconducting polymers in organic
electronics, Chem. Soc. Rev. 40 (2011) 3728-3743.
[34] S.J. Yoon, J.H. Kim, J.W. Chung, S.Y. Park, Exploring the minimal structure of a
wholly aromatic organogelator: simply adding two β-cyano groups to distyrylbenzene, J.
Mater. Chem. 21 (2011) 18971-18973.

[35] T. Putnin, H. Le, T-T. Bui, J.Jakmunee, K. Ounnunkad, S. Péralta, P-H Aubert, F.
Goubard, A. Farcas, Poly(3,4-ethylenedioxythiophene/permethylated β-cyclodextrin)
polypseudorotaxane and polyrotaxane: Synthesis, characterization and application as hole
transporting materials in perovskite solar cells” European Polymer Journal
DOI: 10.1016/j.eurpolymj.2018.06.005
[36] Y. Guo, C. Liu, K. Inoue, K. Harano, H. Tanaka, E. Nakamura, Enhancement in the
efficiency of an organic–inorganic hybrid solar cell with a doped P3HT hole-transporting
layer on a void-free perovskite active layer. J. Mater. Chem. A 2 (2014) 13827–13830.
[37] J. H. Heo, S. H. Im, CH3NH3PbI3/poly-3-hexylthiophen perovskite mesoscopic solar
cells: Performance enhancement by Li-assisted hole conduction Phys. Status Solidi RRL 8,
(2014) 816–821.
[38] N.H. Tiep, Z. Ku, H.J. Fan, Recent Advances in Improving the Stability of Perovskite
Solar Cells, Adv. Energy Mater. 6 (2015) 1–19.
[39] T.A. Berhe, W.-N. Su, C.-H. Chen, C.-J. Pan, J.-H. Cheng, H.-M. Chen, M.-C. Tsai, L.-
Y. Chen, A.A. Dubale, B.-J. Hwang, Organometal halide perovskite solar cells: degradation
and stability, Energy Environ. Sci. 9 (2016) 323–356.
[40] An-Na Cho, Hui-Seon Kim, Thanh-Tuân Bui, Xavier Sallenave, Fabrice Goubard and
Nam-Gyu Park Role of LiTFSI in high Tg triphenylamine-based hole transporting material
in perovskite solar cell RSC Adv. 6 (2016) 68553-68559.