Synthesis of series of low band gap small organic molecules and evaluation of their solar cell activity

Article abstract of DOI:10.14233/ajchem.2016.19931

Organic solar cells have attracted much attention in the recent years but still in search of devices with efficiency comparable to that of silicon solar cells. In this view, a series of highly conjugated imidazolinone molecules were synthesized by a simple in situ coupling method, which resulted in high yield (85-95 %) of the products compared to the traditional method of synthesis. UV-visible studies performed in varying solvents differing in polarity, showing shift in their spectra with change in polarity. The band gap calculated thereafter ranged between 2.8-3.1 eV showing their potential for use in photovoltaic cell. Studies of the I-V characteristics of the photovoltaic devices fabricated with the newly synthesized molecules were performed. The devices with naphthalene substituent showed the highest power conversion efficiency of 0.1 % compared to others, thereby opening up room for use in organic solar cells.

Full text of DOI:10.14233/ajchem.2016.19931

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Asian Journal of Chemistry; Vol. 28, No. 10 (2016), 2223-2227
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19931
Synthesis of Series of Low Band Gap Small Organic
Molecules and Evaluation of their Solar Cell Activity
2
G. SHARMA1,* and J.G. HANDIQUE
1Department of Engineering Chemistry, Institute of Engineering and Technology, Dibrugarh University, Dibrugarh-786 004, India
2Department of Chemistry, Dibrugarh University, Dibrugarh-786 004, India
*Corresponding author: E-mail: gitaleesharma@dibru.ac.in
Received: 26 February 2016;
Accepted: 19 May 2016;
Published online: 30 June 2016;
AJC-17971
Organic solar cells have attracted much attention in the recent years but still in search of devices with efficiency comparable to that of
silicon solar cells. In this view, a series of highly conjugated imidazolinone molecules were synthesized by a simple in situ coupling
method, which resulted in high yield (85-95 %) of the products compared to the traditional method of synthesis. UV-visible studies
performed in varying solvents differing in polarity, showing shift in their spectra with change in polarity. The band gap calculated
thereafter ranged between 2.8-3.1 eV showing their potential for use in photovoltaic cell. Studies of the I-V characteristics of the photovoltaic
devices fabricated with the newly synthesized molecules were performed. The devices with naphthalene substituent showed the highest
power conversion efficiency of 0.1 % compared to others, thereby opening up room for use in organic solar cells.
Keywords: Organic solar cells, Imidazolinone, Band gap, Power conversion efficiency.
Literature reports reveal that small conjugated molecules
like imidazolinones as active layer in device fabrication has
proved to be promising. The reason for this positivity is its
flexibility to molecular property alteration, bio-degradable
ability and user friendliness [10].
We report here the synthesis of nine highly conjugated
imidazolinone molecules by a novel method, which resulted
in high yield of the products. UV-visible studies were performed
in solvents varying in their polarity to find the band gap of the
active layer. The devices showed photovoltaic effect when
exposed to light and their current-voltage (I-V) characteristics
studied. The results showed the potential of these compounds
to be used in organic solar cells (OSCs).
INTRODUCTION
Solar energy has been identified round the globe as an
area of significance in providing solutions to the problem of
meeting future energy needs. Today the most promising tool to
make use of solar energy is its direct conversion into electrical
energy in photovoltaic cells. But until now the photovoltaic
cell have been dominated by solid state junction devices, often
made of silicon. Though the power conversion efficiency of
inorganic solar cells has gone up to 44.7 % in lab [1], their
high energy consumption at fabrication and cost intensiveness
has created a snag to their use in research and development.
The limitations of the inorganic solar cells has been challenged
by a new generation of photovoltaics based on organic com-
pounds. Organic solar cells with π-conjugated materials as
active layer has attracted much attention as a renewable energy
source owing to their low energy consumption at fabrication,
compatibility with flexible substrates, environment friendly
and unlimited variability [2-5].
The recent surge in organic/polymer solar cell research began
with the pioneering work by Tang [6] who developed bilayer
organic semiconductors with an efficiency of around 1 %.
Subsequently, Spanggaard and Krebs devised the first polymer/
C60 based cell [7]. But the power conversion efficiency of organic
solar cells is only 8.4 % in lab and tandem organic solar cell,
11.5 % thereby opening up room for further research [8,9].
EXPERIMENTAL
Detection method: The purity of the compounds was
checked by TLC (ethyl acetate/hexane, 1:9). IR spectra of
samples (solid powders) were recorded on a Shimadzu IR
spectrometer. 1H and 13C NMR spectra were obtained on JNM-
ECS400 spectrometer with TMS as the internal standard and
CDCl3 as the solvent. Elemental analysis was carried on a
EuroEA ElementalAnalyser. Melting points were determined
on melting point apparatus and are not corrected. UV-visible
spectra were recorded on a Double Beam JASCO spectro-
photometer in 2 × 10-5 M methanolic solution.

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2224 Sharma et al.
Asian J. Chem.
General procedure for the preparation of compounds
(a-h): A mixture of oxazolone (1 g, 4.2 mmol), aromatic amine
{naphthylamine (0.31 g, 2.2 mmol) or 4-aminoazobenzene
(0.45 g, 2.3 mmol)} and ZnCl2 (0.18 g, 1.3 mmol) in 10 mL
THF was refluxed at 80-110 °C for 1 h. TLC (10 % acetone/
hexane) check was performed for determining the progress of
the reaction. After 1.5 h, anhydrous ZnCl2 (0.38 g, 2.8 mmol)
and aromatic aldehyde {1-naphthaldehyde (0.55 g, 3.5 mmol)
and 9-anthraldehyde (0.23 g, 1.1 mmol)} and 10 mL THF
was added to the reaction mixture and the reflux continued for
another 3 h at 80-110 °C. TLC showed single spot confirming
the formation of product. The products were recrystallized
with ethyl acetate and hexane.
Orange crystals;Yield 80 %; m.p.: 168-169 °C; 1H NMR (400
MHz, CDCl3): δ 5.66 (d, J = 16.3 Hz, 1H, =CHAr), 6.58 (d, J
= 8.0 Hz, 1H, ArH), 6.66 (d, J = 16.3 Hz, 1H, =CHAr), 7.19
(d, J = 8.2 Hz, 2H, ArH), 7.30 (dd, J = 8.4 Hz, 2.0 Hz, 1H,
ArH), 7.36 (d, J = 8.6 Hz, 1H, ArH), 7.58 (d, J = 8.8 Hz, 1H,
ArH, 7.64 (s, 1H, =CHAr), 7.66 (m, 4H, ArH), 7.67 (m, 4H,
ArH), 7.91 (m, 9H, ArH); 13C NMR (400 MHz, CDCl3): δ
168, 164, 142, 136, 135.5, 134.2, 134, 133.7, 133.4, 132.3,
131.4, 130.9, 129.2, 128.5, 128.3, 128, 126.2, 125.9, 125.6,
125.4, 125.3, 125.1, 124.6, 123.7, 123.4, 120.7, 118.7, 112,
109.4; IR (KBr, νmax, cm–1): 3053, 1716, 1627, 1578, 1405,
918, 776, 734; Anal. calcd. (%) for C40H26N2O: C: 87.25; H,
4.76; N, 5.09; Found: C: 87.21; H, 4.76; N, 5.05.
5-Benzylidene-3-naphthalen-1-yl-2-(2-naphthalen-1-
yl-vinyl)-3,5-dihydro-imidazol-4-one (a): Yellow powder;
Yield 80 %; m.p.: 143-144 °C; 1H NMR (400 MHz, CDCl3): δ
5.60 (d, J = 16.2 Hz, 1H, =CHAr), 6.55 (d, J = 7.8 Hz, 1H,
ArH), 6.61 (d, J = 16.2 Hz, 1H, =CHAr), 7.16 (d, J = 8.0 Hz,
2H, ArH), 7.21 (m, 3H, ArH), 7.28 (d, J = 8.4 Hz, 2H, ArH),
7.36 (d, J = 8.5 Hz, 1H, ArH), 7.55 (d, J = 8.6 Hz, 2H, ArH),
7.60 (s, 1H, =CHAr), 7.66 (m, 4H, ArH),7.68 (m, 4H, ArH);
13C NMR (400 MHz, CDCl3): δ 168, 164, 142, 136, 135.5,
134.9, 134.5, 134, 133.4, 132.3, 130.9, 128.5, 128.4, 128,
127.7, 126.2, 126, 125.9, 125.6, 125.4, 124.6, 123.4, 120.7,
118, 112, 109; IR (KBr, νmax, cm–1): 3057, 1718, 1688, 1641,
1510, 1405, 771, 799, 691; Anal. calcd. (%) for C32H22N2O:
C: 85.31; H, 4.92; N, 6.22; Found: C: 85.28; H, 4.90; N, 6.18.
2-(2-Anthracen-9-yl-vinyl)-5-benzylidene-3-naphthalen-
1-yl-3,5-dihydro-imidazol-4-one (b): Dark Yellow powder;
Yield 85 %; m.p.: 162-163 °C;. 1H NMR (400 MHz, CDCl3):
δ 5.61 (d, J = 16.1 Hz, 1H, =CHAr), 6.58 (d, J = 8.0 Hz, 1H,
ArH), 6.67 (d, J = 16.1 Hz, 1H, =CHAr), 7.20 (d, 8.3 Hz, 2H,
ArH), 7.30 (d, J = 8.5 Hz, 2H, ArH), 7.25 (m, 3H, ArH), 7.65
4-[1-Naphthalen-1-yl-2-(2-naphthalen-1-yl-vinyl)-5-
oxo-1,5-dihydro-imidazol-4-ylidenemethyl]-benzaldehyde
(e): Red Powder;Yield 90 %; m.p.: 160-161 °C; 1H NMR (400
MHz, CDCl3): δ 5.65 (d, J = 16.4 Hz, 1H, =CHAr), 6.58 (d,
J = 7.8 Hz, 1H, ArH), 6.68 (d, J = 16.4 Hz, 1H, =CHAr), 7.17
(d, J = 8.0 Hz, 2H, ArH), 7.27 (dd, J = 8.2 Hz, 1.8 Hz, 1H,
ArH), 7.36 (d, J = 8.5 Hz, 1H, ArH), 7.49 (d, J = 8.7 Hz, 2H,
ArH), 7.56 (d, J = 8.8 Hz, 1H, ArH), 7.63 (s, 1H, =CHAr),
7.67 (m, 4H, ArH), 7.69 (m, 4H, ArH), 7.76 (d, J = 8.7 Hz,
2H, ArH), 9.87 (s, 1H, -CHO); 13C NMR (400 MHz, CDCl3):
δ 190, 168, 164, 142, 140.7, 136, 135.9, 135.5, 134.5, 134.2,
133.4, 132.3, 130.9, 129.6, 128.5, 138.3, 128, 126.7, 126.2,
125.9, 125.6, 125.4, 124.6, 124.4, 123.7, 123.4, 120.7, 118.7,
112, 109.4; IR (KBr, νmax, cm–1): 3253, 3052, 2920, 1674, 1602,
1501, 1379, 825, 771, 540; Anal. calcd. (%) for C33H22N2O2:
C: 82.83; H, 4.63; N, 5.85; Found: C: 82.80; H, 4.62; N, 5.80.
4-[2-(2-Anthracen-9-yl-vinyl)-1-naphthalen-1-yl-5-
oxo-1,5-dihydro-imidazol-4-ylidenemethyl]-benzaldehyde
(f): Red powder;Yield 80 %; m.p.: 175-176 °C; 1H NMR (400
MHz, CDCl3): δ 5.66 (d, J = 16.4 Hz, 1H, =CHAr), 6.58 (d,
J = 8.1 Hz, 1H, ArH), 6.68 (d, J = 16.4 Hz, 1H, =CHAr), 7.20
(d, J = 8.3 Hz, 2H, ArH), 7.48 (d, J = 8.5 Hz, 2H, ArH), 7.64
(s, 1H, =CHAr), 7.67 (m 4H, ArH), 7.78 (d, J = 8.5 Hz, 2H,
ArH), 7.92 (m, 9H, ArH), 9.88 (s, 1H, -CHO); 13C NMR (400
MHz, CDCl3): δ 190, 168, 164, 142, 140.7, 136, 135.9, 134.5,
134.2, 133.7, 132.3, 131.4, 129.6, 129.2, 128.3, 126.7, 126.2,
125.9, 125.6, 125.3, 125.1, 124.6, 123.4, 120.7, 118.7, 109.4;
IR (KBr, νmax, cm–1): 3255, 3050, 1713, 1674, 1627, 1597,
1501, 1377, 825, 771, 542; Anal. calcd. (%) for C37H24N2O2:
C: 84.07; H, 4.58; N, 5.30; Found: C: 84.05; H, 4.53; N, 5.27.
4-[2-(2-Naphthalen-1-yl-vinyl)-5-oxo-1-(4-phenylazo-
phenyl)-1,5-dihydro-imidazol-4-ylidenemethyl]-benzaldehyde
(s, 1H, =CHAr), 7.66 (m, 4H, ArH), 7.90 (m, 9H, ArH); 13
C
NMR (400 MHz, CDCl3): δ 168, 164, 142, 136, 134.9, 134.2,
134, 133.7, 132.3, 131.4, 129.2, 128.4, 128.3, 127.7, 126.2,
125.9, 125.6, 125.3, 125.1, 124.6, 123.4, 120.7, 118.7, 112,
109.4; IR (KBr, νmax, cm–1): 3055, 2925, 2856, 1717, 1631,
1518, 1437, 923, 774, 691; Anal. calcd. (%) for C36H24N2O:
C: 86.38; H, 4.83; N, 5.60; Found: C: 86.34; H, 4.80; N, 5.58.
3-Naphthalen-1-yl-5-naphthalen-1-ylmethylene-2-(2-
naphthalen-1-yl-vinyl)-3,5-dihydro-imidazol-4-one (c):
Orange crystals;Yield 90 %; m.p.: 154-155 °C; 1H NMR (400
MHz, CDCl3): δ 5.65 (d, J = 16.4 Hz, 1H, =CHAr), 6.58 (d, J
= 7.9 Hz, 1H, ArH), 6.68 (d, J = 16.4 Hz, 1H, =CHAr), 7.18
(d, 8.0 Hz, 2H, ArH), 7.27 (dd, J = 8.2 Hz, 1,8 Hz, 1H, ArH),
7.28 (dd, J = 8.2 Hz, 1.8 Hz, 1H, ArH), 7.36 (d, J = 8.5 Hz,
1H, ArH), 7.37 (d, J = 8.5 Hz, 1H, ArH), 7.55 (d, J = 8.6hz,
1H,ArH), 7.56 (d, J = 8.6 Hz, 1H,ArH), 7.64 (s, 1H, =CHAr),
7.66 (m, 4H, ArH), 7.67 (m, 4H, ArH), 7.69 (m, 4H, ArH); 13C
NMR (400 MHz, CDCl3): δ 168, 164, 142, 136, 135.5, 134.5,
134.2, 133.4, 132.3, 128.5, 128.3, 128, 126.2, 125.9, 125.4,
125.6, 125.4, 124.6, 123.7, 123.4, 120.7, 118.7, 112, 109.4;
IR (KBr, νmax, cm–1): 3242, 3001, 1699, 1652, 1507, 1437,
774, 694, 605; Anal. calcd. (%) for C36H24N2O: C: 86.38; H,
4.83; N, 5.60; Found: C: 86.35; H, 4.80; N, 5.55.
1
(g): Red powder; Yield 88 %; m.p.: 150-151 °C; H NMR
(400 MHz, CDCl3): δ 5.65 (d, J = 16.4 Hz, 1H, =CHAr), 6.68
(d, J = 16.4 Hz, 1H, =CHAr), 7.27 (dd, J = 8.2 Hz, 1.8 Hz,
1H, ArH), 7.36 (d, J = 8.5 Hz, 1H, ArH), 7.46 (m, 3H, ArH),
7.49 (d, J = 8.7 Hz, 2H, ArH), 7.55 (d, J = 8.6 Hz, 1H, ArH),
7.58 (d, J = 8.8 Hz, 1H, ArH), 7.64 (s, 1H, =CHAr), 7.67 (m,
4H, ArH), 7.76 (d, J = 9.0 Hz, 2H, ArH), 7.84 (d, J = 8.6 Hz,
2H, ArH), 7.91 (d, J = 8.6 Hz, 2H, ArH), 7.93 (d, J = 8.6 Hz,
2H, ArH), 9.87 (s, 1H, -CHO); 13C NMR (400 MHz, CDCl3):
δ 190, 168, 164, 152.5, 148.1, 140.7, 136, 135.9, 135.5, 133.4,
132.3, 130.9, 130.7, 129.6, 128.8, 128.5, 128, 126.7, 125.9,
125.6, 125.4, 123.7, 123.4, 122.9, 122.7, 120.7, 112; IR (KBr,
2-(2-Anthracen-9-yl-vinyl)-3-naphthalen-1-yl-5-
naphthalen-1-ylmethylene-3,5-dihydro-imidazol-4-one (d):
ν
max, cm–1): 3263, 3050, 1671, 1598, 1503, 1380, 828, 768,

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Vol. 28, No. 10 (2016)
Synthesis of Series of Low Band Gap Small Organic Molecules 2225
694, 544;Anal. calcd. (%) for C35H24N4O2: C: 78.93; H, 4.54,;
N, 10.52; Found: C: 78.90; H, 4.50; N, 10.48.
and terephthaldehyde were synthesized in bulk (Scheme-I)
[11].
4-[2-(2-Anthracen-9-yl-vinyl)-5-oxo-1-(4-phenylazo-
phenyl)-1,5-dihydro-imidazol-4-ylidenemethyl]benzal-
dehyde (h): Red powder; Yield 82 %; m.p.: 170-171 °C; H
O
R
O
1
Benzaldehyde/
naphthaldehyde/
terepthaldehyde
110 oC / 2 h
OH
CH3
N
O
NMR (400 MHz, CDCl3): δ 5.66 (d, J = 16.3 Hz, 1H, =CHAr),
6.66 (d, J = 16.3 Hz, 1H, =CHAr), 7.45 (m, 3H, ArH), 7.47
(d, J = 8.6 Hz, 2H, ArH), 7.65 (s, 1H, =CHAr), 7.76 (d, J =
8.8 Hz, 2H, ArH), 7.83 (d, J = 8.5 Hz, 2H, ArH), 7.90 (d, J =
8.5 Hz, 2H, ArH), 7.92 (d, J = 8.4 Hz, 2H, ArH), 7.94 (m, 9H,
ArH), 9.88 (s, 1H, -CHO); 13C NMR (400 MHz, CDCl3): δ
190, 167, 163, 152.5, 148.1, 140.7, 140.4, 136, 135.9, 134.5,
133.7, 132.3, 131.4, 130.7, 129.6, 129.2, 128.8, 128.3, 126.7,
126.2, 125.9, 125.3, 125.1, 122.9, 122.7, 120.7, 112; IR (KBr,
HN
Ac2O / NaOAc
H3C
O
R = H, Ph, PhCHO
Oxazolone (X)
Acetylglycine
Scheme-I: Preparation of substituted oxazolone
The third step includes the in situ synthesis of the highly
conjugated imidazolin-5-one compounds in presence of an
inert solvent THF by Lewis acid catalyzed vinylogous conden-
sation [12] (Scheme-II).
After the synthesis of eight products by in situ method, a
fourth step Aldol condensation reaction was performed with
compound e and acetone as the starting materials in order to
introduce further conjugation to e (Scheme-III). The reason for
selecting e as the starting material was its high yield compared
to the others. The results showed the formation of the aldol
product.
UV-visible studies of all the compounds in solution state
were performed in a double beam JASCO spectrophotometer.
Compound c exhibited a λmax value of 439 nm, which provided
the lowest band gap value of 2.83 eV compared to all other
compounds. The results of UV-visible studies for all the nine
compounds in methanol are depicted in Table-1.
ν
max, cm–1): 3263, 3052, 1674, 1597, 1501, 1379, 976, 828,
767, 697; Anal. calcd. (%) for C39H26N4O2: C: 80.39; H, 4.50;
N, 9.62; Found: C: 80.35; H, 4.48; N, 9.60.
Procedure for the preparation of compound (i): 2 M
NaOH (1 mL, 1.74 mmol) was added slowly under stirring
condition to compound e (0.5 g, 1.05 mmol) in 10 mL ethanol.
To the reaction mixture acetone (0.2 mL, 3.44 mmol) was
added and stirring continued for 45 min. The reaction mixture
was cooled in ice-cold water bath followed by filtration. The
residue was washed with ice-cold solution of 5 % acetic acid
and ethanol and then dried overnight in air. TLC (10 % acetone/
hexane) showed single spot confirming the formation of
product.
3-Naphthalen-1-yl-2-(2-naphthalen-1-yl-vinyl)-5-[4-
(3-oxo-but-1-enyl)-benzylidene]-3,5-dihydro-imidazol-4-
one (i): Dark yellow;Yield 80 %; m.p.: 190-191 °C; 1H NMR
(400 MHz, CDCl3): δ 2.0 (s, 1H, -OH), 3.03 (d, J = 7.5 Hz,
1H, -CH), 5.04 (t, J = 7.1 Hz, 2H, -CH2), 5.65 (d, J = 16.4 Hz,
1H, =CHAr), 6.58 (d, J = 7.8 Hz, 1H, ArH), 6.68 (d, J 16.4
Hz, 1H, =CHAr), 7.14 (d, J = 8.2 Hz, 2H, ArH) 7.17 (d, 8.0
Hz, 2H, ArH), 7.23 (d, J = 8.2 Hz, 2H, ArH), 7.23 (d, J = 8.2
Hz, 2H, ArH); 7.27 (dd, J = 8.2 Hz, 1.8 Hz, 1H, ArH), 7.36 (d,
J = 8.5 Hz, 1H, ArH), 7.44 (m, 3H, ArH), 7.56 (d, J = 8.7 Hz,
1H, ArH), 7.63 (s, 1H, =CHAr), 7.67 (m, 4H, ArH), 7.69 (m,
4H, ArH), 7.89 (d, J = 8.4 Hz, 2H, ArH) 13C NMR (400 MHz,
CDCl3): δ 197.6, 169, 160, 142.5, 140.1, 137.4, 136, 135.5,
134.5, 134.2, 133.8, 133.4, 132.9, 132.3, 130.9, 128.6, 128.5,
128.4, 128.3, 128, 127.2, 126.4, 126.2, 125.9, 125.6, 125.4,
124.6, 123.7, 123.4, 120.7, 118.7, 112, 109.4, 69.2, 48.4; IR
(KBr, νmax, cm–1): 3300, 3229, 3050, 1674, 1597, 1500, 1375,
809, 770, 542; Anal. calcd. (%) for C41H30N2O3: C: 80.39; H,
4.50; N, 9.62; Found: C: 80.35; H, 4.48; N, 9.60.
Device fabrication and electrical characterization:The
photovoltaic devices were fabricated using the formula: ITO
(130 nm) || WPTA (90 nm) || PEDOT:PSS (60 nm) || Organic
layer (100 nm) ||Al (100 nm). The current-voltage (I-V) charac-
teristics of the photovoltaic solar cell were measured using a
Keithley model 2420 source meter under day sunlight of 100
mW/cm2 illumination. The solar illumination was measured
by using a lux meter. In this study, the film thickness of the W-
PTA and PEDOT:PSS layer was controlled by varying the weight
percent of their solutions during the spin-coating process while
all other experimental conditions, such as rpm (3000 rpm) for
30 s and annealing temperature (115 °C), were fixed. The spin
coating rpm of the organic layer was maintained at 1000 rpm
for 60 s.
Table-2 shows a comparison of the I-V characteristics of
the photovoltaic devices fabricated with nine different organic
molecules.
Table-2 showed that the power conversion efficiency of
the devices made with the nine molecules are in the order of
Dc > Db > Dd > Dh > Dg > Da > De > DI > Df. The reason for
device “Dc” showing the highest power conversion efficiency
is because of the highest conjugation of compound “c” com-
pared to all other imidazoline molecules used for devising the
organic solar cell devices. The I-V characteristics of the device
Dc is shown in Fig. 1.
RESULTS AND DISCUSSION
Synthesis: Design and synthesis of nine highly conjugated
molecules in three steps are reported. Firstly, acetylglycine
was prepared by the traditional method [11]. Next oxazolone
with three different aldehydes, benzaldehyde, naphthaldehyde
TABLE-1
UV-VISIBLE STUDIES OF ALL THE NINE COMPOUNDS SYNTHESIZED
Compounds
max (nm)
Band gap
a
b
c
d
e
f
g
h
i
355
3.50
430
2.96
439
2.83
405
3.07
330
3.76
278
4.47
333
3.73
344
3.61
279
4.45
λ

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2226 Sharma et al.
Asian J. Chem.
O
N
O
N
N
N
Napthaldehyde
Napthaldehyde
Anhy
ZnCl
(a)
(c)
Napthylamine
Napthylamine
X (R=H)
X (R=Ph)
1
2
2
O
O
N
N
reflux 1hr
N
N
9-Anthraldehyde
9-Anthraldehyde
0
at 90-110 C
(d)
(b)
OHC
OHC
O
O
N
N
N
N
Napthaldehyde
Napthaldehyde
N
N
X (R=PhCHO)
2
(g)
Anhy
ZnCl
2
(e)
N
Napthylamine
4-Phenylazo-phenylamine
reflux 1hr
0
O
at 90-110 C
OHC
N
OHC
O
N
9-Anthraldehyde
9-Anthraldehyde
N
N
N
(h)
(f)
Scheme-II: Preparation of π-conjugated imidazolinone compounds
TABLE-2
I-V CHARACTERISTICS OF THE NINE DEVICES
Power conversion
efficienc (η, %)
Organic solar
cell device
Power maximum
(Pmax
VOC [V]
JSC [mA cm-2]
Fill factor
)
Da
Db
Dc
Dd
De
Df
Dg
Dh
Di
0.25
1.60
3.60
0.43
0.15
0.09
0.07
0.28
0.10
1.00
0.98
0.90
0.94
0.95
0.95
0.92
1.00
0.95
0.27
0.29
0.29
0.30
0.31
0.31
0.31
0.30
0.31
0.07
0.46
0.95
0.12
0.04
0.03
0.02
0.08
0.03
0.007
0.050
0.100
0.010
0.004
0.003
0.002
0.008
0.003
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
O
O
N
N
Aldol condensation
acetone
Compound e
(i)
Scheme-III: Preparation of the aldol product of e
The bad gap values as observed from Table-1 also satisfies
this justification as compound “c” shows the lowest band gap
value of all. The WPTA layer in between the ITO and PEDOT:
PSS layer could function as a stairway for hole transport in
polymer solar cells.
0
0
1
2
3
4
5
Voltage (V)
Fig. 1. I-V curve of the device Dc