A novel porphyrin dye with phenoxazine as donor unit for efficient dye-sensitized solar cells

Article abstract of DOI:10.1016/j.dyepig.2021.109308

A novel porphyrin dye T-2 with phenoxazine (POZ) as donor unit has been synthesized and utilized for dye-sensitized solar cells (DSSC). Compare with porphyrin dye T-1 (in which triphenylamine as a donor unit), the DSSC based on T-2 exhibited a significant

Full text of DOI:10.1016/j.dyepig.2021.109308

Dyes and Pigments 190 (2021) 109308
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
A novel porphyrin dye with phenoxazine as donor unit for efficient
dye-sensitized solar cells
a
,
1
b
,
1
a
a
d
b,*
Shengzhong Li , Shuangyu Zhang , Shu Mei , Xiangfei Kong , Miao Yang , Wenjun Wu
,
c,
**
a,***
Shuhua Zhang
, Haijun Tan
a
Guangxi Key Laboratory of Electrochemical and Magneto-chemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology,
Guilin, 541004, China
b
School of Chemistry and Molecular Engineering, East China University of Science & Technology, Shanghai, 200237, China
c
College of Chemistry, Guangdong University of Petrochemical Technology, Maoming, Guangdong, 525000, China
d
Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI, 53706, United States
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel porphyrin dye T-2 with phenoxazine (POZ) as donor unit has been synthesized and utilized for dye-
sensitized solar cells (DSSC). Compare with porphyrin dye T-1 (in which triphenylamine as a donor unit), the
Porphyrin dye
Phenoxazine
ꢀ 2
DSSC based on T-2 exhibited a significantly higher Jsc (16.35 mA cm ) and Voc (670 mV) than that of T-1 (9.13
Donor unit
ꢀ 2
mA cm , 610 mV), which attribute to the higher IPCE and
τ
of the device based on T-2. Correspondingly, the T-
Dye-sensitized solar cells
2
-based device achieved a photoelectric conversion efficiency (PCE) of 7.64% (N719, 8.45%). By detailed
investigation of the relationship between structure and performance, we found the butterfly-shaped structure,
stronger electron-donating capability, and the extra alkyl chain of POZ are the main reasons leading to better
performance of T-2 than that of T-1 in the DSSC device.
1
. Introduction
Porphyrin dyes have been attracted much attention because of their
electron-withdrawing acceptors to reduce the HOMO-LUMO band gap
and enhance the ICT process [8]. So far, many electron-rich groups such
as diphenylamine [9,10], triphenylamine [11–15], carbazole [16–18],
indoline [19,20], cyanine [21,22] and phenothiazine [23–27] are
widely used as electron donors in porphyrin dyes to promote the
excellent photovoltaic properties [1,2], and their advantages are mainly
reflected in: (i) A strong light absorption capability from visible to
near-infrared region, (ii) The β-position and Meso-position of the core
are easy to modify, (iii) Fine-tuning of the electronic properties [3].
Since the invention of DSSC by Gr a¨ tzel and co-workers in 1991, various
porphyrin dyes have been synthesized and applied in DSSC [4]. Among
them, SM315 achieves a PCE of 13.0% under simulated sunlight con-
ditions [5]. In addition, the tandem DSSC formed by the metal-free
organic dye SGT-137 (as the top battery) and porphyrin dye SGT-021
2
transmission and injection of electrons toward the surface of TiO .
Among them, the nitrogen-anthracene electron donor has a special
butterfly-shaped configuration, which is widespread adoption for DSSC
[7,28,29]. Xie and co-workers synthesized
a
series of
phenothiazine-based porphyrin sensitizers. A molecular engineering
approach has also been demonstrated to improve the performance of
phenothiazine-based porphyrin sensitizers. For instance, the introduc-
tion of alkyl chain into the donor (D) unit or ortho-positions of the
meso-phenyl moieties is an effective way to suppress dye aggregation
and charge recombination, which improves the photovoltaic behavior of
DSSC [30,31]. Besides, electrochemical, photophysical, and photovol-
taic investigations indicate that the introduction of additional acceptors
can effectively extend the absorption spectra, resulting in better sunlight
(
as the bottom battery) was proved to have an efficiency of 14.64% [6],
which is extremely close to the commercialized target efficiency of
5.0%. It is well-known that rationally optimizing the molecular struc-
1
ture by molecular engineering can effectively improve its performance
of porphyrin dyes [7]. Commonly, the design of porphyrin sensitizers
often includes introducing electron-rich donors and strong
*
Corresponding author.
*
*
* Corresponding author.
** Corresponding author.
E-mail addresses: wjwu@ecust.edu.cn (W. Wu), zsh720108@163.com (S. Zhang), navytan@glut.edu.cn (H. Tan).
1
Shengzhong Li and Shuangyu Zhang contributed equally to this work.
https://doi.org/10.1016/j.dyepig.2021.109308
Received 11 February 2021; Received in revised form 10 March 2021; Accepted 10 March 2021
Available online 16 March 2021
0
143-7208/© 2021 Elsevier Ltd. All rights reserved.

S. Li et al.
Dyes and Pigments 190 (2021) 109308
harvesting [32]. Recently, they reported an alternative approach for
developing efficient DSSC by designing a class of “concerted companion
dyes”, which achieve a remarkable efficiency of 12.4% [33]. This series
of studies provide many essential strategies for the molecular engi-
neering of porphyrin dyes. Our previous work reported that Phenoxazin,
which also belongs to nitrogen anthracene, exhibits better photovoltaic
performance than phenothiazine for DSSC [34].
measurement was performed by a Newport-74125 system (Newport
Instruments). Electrochemical impedance spectroscopy (EIS) was
measured with a two-electrode system in the dark by Electrochemical
Workstation (Zahner IM6e) [39].
3. Results and discussion
Inspired by the discussion above, we introduced the phenoxazine as a
D unit to the porphyrin dye for the first time and prepared a novel zinc
porphyrin dye T-2 (Fig. 1). In addition, we systematically analyzed the
photophysical, electrochemical properties and the performance of T-2 in
DSSC. Furthermore, we simultaneously carried out a comparative
analysis with T-1 (triphenylamine (TPA) as D unit).
3.1. Dye structures and syntheses
The synthesis of dyes T-1 and T-2 are summarized in Scheme 1. The
POZ was synthesized following our published procedure [34], porphyrin
core, and the A- -A unit was synthesized via procedures from the liter-
π
ature [30,40]. The synthetic details are shown in Scheme S1, and the
results of intermediates are provided in the Supporting.
2
. Experimental
Compound 11. Compound 5 (0.75 g, 0.53 mmol), compound 10
(
0.12 g, 0.42 mmol), Pd
2
(dba)
3
(0.19 g, 0.21 mmol) and AsPh
3
(0.28 g,
2
.1. Materials
0.90 mmol) were dissolved in THF (60 mL) and Et
3
N (20 mL). After the
◦
solution was stirred at 55 C under argon for 6 h. The solvent was
removed under reduced pressure and the residue was purified by column
All reagents and chemicals were purchased from Aladdin or Energy
chemical reagent platform and used without further purification. All
solvents were dried and freshly distilled prior to use. All column chro-
matographic separations were performed using Merck silica gel (60–120
mesh).
chromatography on silica gel using petroleum ether/CH
give compound 11 as green powders (0.22 g, yield: 25.5%). H NMR
(CDCl
, 500 MHz, ppm) δ 10.03–10.01 (d, 2H), 9.63–9.60 (d, 2H),
9.00–8.98 (d, 2H), 8.88–8.87 (d, 2H), 8.18–8.16 (d, 1H), 8.09–8.06 (d,
H), 7.99–7.95 (d, 2H), 7.76–7.73 (s, 3H), 7.08–7.04 (d, 4H), 4.01–3.98
2 2
Cl (1:1, v:v) to
1
3
2
(
s, 3H), 3.92–3.89 (m, 8H), 1.35–1.02 (m, 28H), 1.01–0.88 (m, 18H),
2
.2. Device assembly and measurements
0
.86–0.74 (m, 20H), 0.65–0.35 (m, 26H). MS: m/z = 1633.77.
Compound 13a. Compound 11 (83.00 mg, 0.05 mmol), compound
2
The procedure for preparation of TiO electrodes were adapted from
1
3
2a (0.25 g, 0.10 mmol) and CH COOK (14.70 mg, 0.15 mmol) were
that reported by Gr a¨ tzel and co-workers [35] and the detailed processes
of device fabrication for photovoltaic measurements were very similar
to the previous articles [15,36–38]. A screen-printed double layer of
dissolved in THF/H
2
O (33 mL, 10/1, v/v) and Pd(pph
3
)
4
(115.56 mg,
◦
0
.10 mmol) were added at 70 C under argon for 12 h. Then the solvent
was removed under reduced pressure, and the residue was dissolved in
CH Cl and washed with water, dried over anhydrous Na SO and
evaporated. The residue was purified by column chromatography on
silica gel using petroleum ether/CH Cl (1:1, v:v) to give compound 13a
as green powders (74.30 mg, yield: 82.7%). H NMR (CDCl
TiO
2
particles was used as the photoelectrode. A 12- m thick film of
μ
2
2
2
4
1
3-nm-sized TiO
2
particles was first printed on the FTO conducting
◦
glass, which was kept in a clean box for 5 min, and then dried at 125 C
2
2
over 6 min, and further coated by a 5-
μ
m thick second layer of 400-nm
1
3
, 500 MHz,
light-scattering anatase particles. Finally, the electrodes coated with the
ppm) δ 10.16–10.13 (d, 1H), 10.11–10.09 (d, 1H), 9.28–9.24 (d, 1H),
◦
TiO
2
pastes were gradually sintered in a muffle furnace at 275 C for 5
9
1
.12–9.07 (d, 1H), 9.06–9.03 (d, 1H), 9.00–8.97 (d, 1H), 8.96–8.92 (d,
H), 8.88–8.85 (d, 1H), 8.33–8.28 (t, 1H), 8.07–8.21 (t, 2H), 8.18–8.15
◦
◦
◦
min, at 325 C for 5 min, at 375 C for 5 min, at 450 C for 15 min and at
◦
2
5
00 C for 15 min, respectively. The size of the TiO
2
film was 0.25 cm .
(
d, 1H), 8.09–8.04 (d, 1H), 7.96–7.90 (t, 1H), 7.76–7.70 (t, 2H),
◦
These films were immersed into a 40 mM aqueous TiCl
4
solution at 70 C
7
2
.43–7.41 (d, 4H), 7.34–7.31 (d, 1H), 7.24–7.20 (t, 2H), 7.17–7.12 (t,
H), 7.08–7.06 (d, 2H), 7.05–7.04 (d, 2H), 4.03–4.00 (s, 3H), 3.93–3.84
for 30 min, washed with water and ethanol, and then heated again at
◦
4
50 C for 30 min. The films were then immersed into a 300
μM solution
(
m, 8H), 1.25–1.12 (m, 10H), 1.08–0.97 (m, 20H), 0.93–0.86 (m, 10H),
of T-1 or T-2 in a mixture of chloroform and ethanol (volume ratio of 3 :
) for 10 h at room temperature. The seal uses a 45 mm thick Bynel
DuPont) hot melt gasket to fill the electrolyte into the interior space
through a vacuum backfill system. The osmotic electrolyte consisted:
.6 M dimethylpropylimidazolium iodide, 0.05 M I2, 0.1 M LiI, and 0.5
0
.84–0.77 (m, 24H), 0.70–0.62 (m, 8H), 0.61–0.47 (m, 16H), 0.46–0.38
7
(
m, 8H).MS: m/z = 1796.97.
(
Dye T-1. Compound 13a (74.30 mg, 41.35
μ
mol) and LiOH⋅H
2
O
(
69.40 mg, 1.65 mmol) were dissolved in THF (30 mL) and H
2
O (2 mL),
0
◦
respectively. Then the mixed solution was stirred at 55 C under argon
for 6 h. Then the solvent was removed under reduced pressure, and the
M tert-butylpyridine in acetonitrile. 4 parallel cells for each dye mole-
cule will be prepared to obtain more reasonable and credible data.
Under standard AM 1.5 simulated solar irradiation (WXS155S-10),
photocurrent density-voltage (Jꢀ V) curves of solar cell devices were
measured by Keithley 2400 Source Meter Instruments. Monochromatic
incident photon-to-current conversion efficiency (IPCE) spectra
residue was dissolved in CH
anhydrous Na SO and evaporated. The residue was purified by column
chromatography on silica gel using CH Cl /MeOH (20:1, v:v) to give T-1
as green powders (64.95 mg, yield: 88.1%). H NMR (CDCl
2 2
Cl and washed with water, dried over
2
4
2
2
1
3
, 500 MHz,
Fig. 1. Molecular structures of the T-1 and T-2.
2

S. Li et al.
Dyes and Pigments 190 (2021) 109308
Scheme 1. Synthetic routes of T-1 and T-2.
ppm) δ 10.12–10.09 (d, 1H), 10.07–10.03 (d, 1H), 9.05–9.03 (d, 1H),
9
2
.02–9.00 (d, 1H), 8.99–8.96 (d, 1H), 8.95–8.93 (d, 1H), 8.90–8.85 (m,
H), 8.30–8.26 (d, 1H), 8.25–8.20 (d, 2H), 8.16–8.10 (d, 3H), 8.09–8.03
(
d, 2H), 7.93–7.86 (t, 2H), 7.79–7.70 (m, 4H), 7.42–7.38 (m, 6H),
7
.08–7.02 (m, 6H), 3.91–3.87 (t, 8H), 1.25–1.12 (m, 10H), 1.08–0.97
(
m, 20H), 0.93–0.86 (m, 10H), 0.84–0.77 (m, 20H), 0.70–0.62 (m, 8H),
0
.61–0.47 (m, 16H), 0.46–0.38 (m, 8H). MS: m/z = 1782.95.
Compound 13b. Compound 13b was synthesized following the
same procedure as that for compound 13a, except that compound 12b
0.25 g, 0.60 mmol) was used instead of compound 12a. Green powders,
(
1
yield: 48.76 mg, 87.9%. H NMR (CDCl
3
, 500 MHz, ppm) δ 10.18–10.13
(
d, 2H), 9.20–9.14 (d, 1H), 9.07–9.03 (m, 3H), 8.99–8.94 (d, 1H),
8
2
.86–8.84 (d, 1H), 8.35–8.32 (d, 1H), 8.30–8.27 (d, 2H), 8.22–8.19 (d,
H), 8.01–7.95 (t, 3H), 7.78–7.73 (d, 1H), 7.40–7.35 (d, 1H), 7.08–7.04
d, 2H), 6.92–6.88 (d, 2H), 6.75–6.71 (d, 3H), 6.66–6.63 (d, 1H),
(
6
1
0
.56–6.53 (d, 1H), 4.03–4.02 (s, 3H), 3.97–3.76 (m, 8H), 2.07–2.02 (m,
H), 1.35–1.25 (m, 46H), 0.93–0.88 (m, 15H), 0.82–0.77 (m, 15H),
.70–0.61 (m, 8H), 0.55–0.43 (m, 16H). MS: m/z = 1847.04.
Fig. 2. UV–vis absorption spectra of PTZ-3 and PTZ-5 in THF.
Dye T-2. T-2 was synthesized following the same procedure as that
Table 1
Photophysical and electrochemical date of T-1 and T-2.
for T-1, except that compound 13b (48.76 mg, 26.37
instead of compound 13a. Green powders, yield: 41.47 mg, 85.7%. H
NMR (CDCl
, 500 MHz, ppm) δ 10.17–10.13 (d, 1H), 10.11–10.07 (d,
H), 9.07–9.02 (d, 2H), 9.02–8.99 (t, 1H), 8.98–8.94 (d, 1H), 8.89–8.80
μ
mol) was used
1
λabs
/
a
abs
a
pl
a
E0ꢀ 0
/eV
b
EOX
c
∗
E
OX
d
dye
ε
λ
3
max
max
max
ꢀ
1
ꢀ 1
nm
/M cm
/nm
711
/V
/V
1
(
m, 2H), 8.35–8.27 (m, 3H), 8.22–8.20 (d, 1H), 8.02–7.94 (m, 2H),
T-1
T-2
433
648
431
1.05969.25
36702.25
115,595
1.84
1.85
0.61
0.63
ꢀ 1.23
ꢀ 1.22
7
1
.77–7.70 (m, 2H), 7.60–7.54 (t, 1H), 7.53–7.47 (t, 1H), 7.22–7.18 (d,
H), 7.06–7.01 (d, 2H), 6.91–6.88 (d, 1H), 6.75–6.69 (d, 3H), 6.67–6.64
708
6
45
37861.5
(
d, 1H), 6.58–6.53 (d, 1H), 3.99–3.78 (t, 8H), 1.97–1.91 (m, 1H),
1
0
.35–1.25 (m, 46H), 0.93–0.88 (m, 15H), 0.82–0.77 (m, 15H),
.70–0.61 (m, 8H), 0.55–0.43 (m, 16H). MS: m/z = 1833.03.
a
abs
The maximum absorption wavelength (λ
), the maximum molar absorp-
max
abs
pl
tion coefficient (
ε
) and the maximum emission wavelength (λ ) were
max
max
derived from the steady-state absorption-emission spectra of the dye in THF. The
molar absorption coefficient( ) were calculated by the equation
ε
ε = A/(cl),
3
.2. Optical properties
where A is absorbance, c is concentration in moles per liter and l is path length in
centimeters.
Fig. 2 shows the UV–vis absorption spectra of T-1 and T-2 in the
b
The 0-0 transition energy (E0-0) was estimated from the intersection of the
tetrahydrofuran (THF) solution. Table 1 summarize their corresponding
normalized absorption and emission spectra.
abs
c
+
absorption maxima (λ ) and molar absorptivity (
ε
) of Soret and Q
The ground state redox electricity (EOX) was referenced to Fc /Fc.
max
d
∗
∗
bands. These porphyrin dyes exhibit an intensive Soret band at 400–550
The excited redox potential (EOX) was derived from the formula EOX = EOX ꢀ
abs
max
ꢀ 1
ꢀ 1
abs
max
E0ꢀ 0/e without considering the entropy change in the light excitation process.
nm (T-1, λ
= 433 nm,
ε
= 105869.25 M cm ; T-2, λ
= 431 nm;
ꢀ 1
ꢀ 1
ε
= 115,595 M
cm ), due to the characteristic
π
ꢀ π
* transition
transitions of the conjugated molecule and intramolecular charge
transfer from the donor unit to the acceptor unit of dyes. Our spectral
test results show that the two dyes have almost the same spectral
localized mainly at the porphyrin core. A moderate Q-band at 600–750
abs
max
ꢀ 1
ꢀ 1
abs
max
nm (T-1 λ
= 648 nm,
ε
= 36702.25 M cm ; T-2λ
= 645 nm, ε
ꢀ 1
ꢀ 1
=
37861.5 M
cm ), which is attributed to
πꢀ π
* charge-transfer
3

S. Li et al.
Dyes and Pigments 190 (2021) 109308
response range, and the
ε
of T-2 is slightly higher than that of T-1,
especially in the range of 400–600 nm. Moreover, the steady-state
emission spectra of T-1 and T-2 dyes were measured in THF and are
shown in Fig. S12 and Table 1. The optical band gap width (E0ꢀ 0) can be
estimated from the intersections of the normalized UV–visible absorp-
tion spectrum and emission spectrum, as shown in Fig. 3. According to
the transition bandgap formula: E0ꢀ 0 = 1240/λ, the calculated E0ꢀ 0 of
T-1 and T-2 are 1.84 and 1.85 eV, respectively.
3
.3. Electrochemical properties
To obtain the electrochemical properties of T-1 and T-2, we con-
ducted measurements using cyclic voltammetry (CV). Table 1 and Fig. 4
summarize the CV results of T-1 and T-2. Both T-1 and T-2 exhibit
reversible waves for the first oxidation peaks (EOX), corresponding to the
HOMO of the dye and indicating that oxidation happens at the donor.
The estimated ground state oxidation potentials EOX of T-1 and T-2 are
Fig. 4. Cyclic voltammetry of T-1 and T-2 in THF.
0
.61 and 0.63 V, respectively, versus the normal hydrogen electrode
(
NHE). Hence, both T-1 and T-2 show sufficiently higher potentials than
ꢀ
ꢀ
3
redox electrolyte (0.4 V) redox couple, indicating enough
the I /I
ꢀ
ꢀ
driving force for regenerating the oxidized dyes by I /I
3
redox elec-
∗
trolytes. The expression E = EOX ꢀ E0ꢀ 0/e was used to calculate the
OX
∗
excited state oxidation potential (E ) of T-1 and T-2, and the corre-
OX
sponding values are ꢀ 1.71 and ꢀ 1.70 V, respectively. Thus, there are
enough driving forces for injecting electrons from T-1 and T-2 into the
conduction band edge (ECB) of TiO
.4. Theoretical calculations
To gain insight into the molecular structures as well as the influence
2
(ꢀ 0.5 V) (Fig. 5).
3
of different substituents on the electron distribution of dyes T-1 and T-2,
we performed DFT and TD-DFT calculations using the functional basis
set B3LYP/6-31G(d, p). Figs. 6 and 7 show the optimized molecular
structure and frontier molecular orbitals (FMOs) of T-1 and T-2 dyes. As
shown in Fig. 7, the HOMO orbitals are mainly distributed in the donor
unit and the porphyrin macrocycle. In contrast, the LUMO orbitals are
predominantly delocalized over the acceptor unit and the porphyrin
macrocycle. This distribution means that the electrons can be effectively
transported from the HOMO orbital to the LUMO orbital. In other words,
the electronic transfer process from the donor to the benzoic acid
acceptor can be easily transported, followed by facilitating the electron
Fig. 5. Energy diagrams of T-1 and T-2.
.5. Photovoltaic performance of DSSC
The dyes were used to fabricate DSSC, and the corresponding
injection from the dyes to the TiO
2
surface. The simulated UV–vis ab-
sorption spectra of the dyes in THF solvent are presented in Fig. S13 and
the corresponding data are collected in Table S1. The intense Soret band
around 450 nm and moderate Q-band around 600 nm corresponds to the
local excitation of the zinc-porphyrin and intramolecular charge trans-
fer, respectively, which are very consistent with our spectral test results.
3
photovoltaic parameters are summarized in Table 2. Figs. 8 and 9 show
the photocurrentꢀ voltage curves (J-V) and the incident photon-to-
current conversion efficiency (IPCE) action spectra. Both T1 and T2
show a broad IPCE action spectrum from 300 nm to 800 nm, suggesting
that they can effectively convert visible light into photocurrent. The
IPCE values of T-2 are significantly higher than those of T-1, which is
mainly attributed to the higher of T-2 and the extra alkyl chain on POZ,
ε
which can suppress the recombination of interfacial electrical to reduce
the dark current. Therefore, T-2 exhibited higher IPCE and short-circuit
ꢀ 2
current density (Jsc) values of 16.35 mA cm . Open-circuit voltage (Voc
)
is also an essential parameter for DSSC. Compared with T-1 (Voc = 610
mV; PCE = 4.12%), T-2 exhibited higher Voc of 670 mV and PCE of
7
.64%.
3
.6. Electrochemical impedance spectroscopy
To further understand the photovoltaic behavior of DSSC based on
these two dyes, we performed electrochemical impedance spectroscopy
Fig. 3. Normalized electronic absorption and emission spectra of the T-1 and T-
(EIS) in the dark. As we all know, the Voc of DSSC represents the po-
2
in THF.
f 2
tential difference between the quasi-Fermi level (E ) of TiO and the
4

S. Li et al.
Dyes and Pigments 190 (2021) 109308
Fig. 6. Simulated optimized structure structure of dyes.
Fig. 7. Electron cloud distribution of dyes at the B3LYP/6-31G(d,p) level with Gaussian09.
Table 2
ꢀ 2
Photovoltaic parameters of cells measured at an irradiation of 100 mW cm
,
simulated AM 1.5 sunlight.
sc/mA⋅cmꢀ
2
FF%
PCE%
dyes
V
oc/V
J
T-1
0.61 ± 0.03
0.67 ± 0.01
0.71
9.13 ± 0.66
16.35 ± 1.90
16.92
73.45 ± 4.62
70.13 ± 0.7
70.45
4.12 ± 0.28
7.64 ± 0.69
8.45
T-2
N719
Fig. 9. Incident photon-to-electron conversion efficiency (IPCE) spectra of the
dyes T-1 and T-2.
shown in Fig. 10a, the C
which indicates a negligible impact of the conduction band position of
TiO on Voc variation. In addition, the dependence of electron lifetimes
) on bias voltage is plotted in Fig. 10b. In general, a longer electron
lifetime implies a slower charge recombination rate at the dye-sensitized
TiO of T-2 causing higher injected
μ
of the T-1 and T-2 DSSCs are almost identical,
2
(
τ
2
ꢀ electrolyte interface. The longer τ
Fig. 8. J–V characteristics measured under irradiation of 100 mW cmꢀ 2
simulated AM 1.5 sunlight.
electron density (Fig. 10b), which is consistent with that of Voc, ranking
as T-1 < T-2. These results indicate that the charge recombination
process determined the Voc values of DSSC.
redox electrolyte. Since the redox electrolyte is fixed in the experiment,
4
. Conclusions
the change of Voc is related to the value of E
the chemical capacitance (C ). Besides, Voc is in connection with elec-
tron lifetime ( ), which can reflect the injected electron density. As
f
, which can be inferred from
μ
In summary, a novel porphyrin sensitizer (T-2) containing a
τ
5

S. Li et al.
Dyes and Pigments 190 (2021) 109308
2
Fig. 10. TiO capacitance (a) and electron lifetime (b) as a function of potential based on dyes T-1 and T-2.
phenoxazine (POZ) as an electron donor has been designed and syn-
thesized for DSSC. Compared to T-1 with triphenylamine donor unit, T-2
exhibits higher efficiency of 7.64% due to the distinctive structure and
strong electron-donating capability of POZ. Our results indicate that
POZ is a very promising donor unit for developing high-efficiency
porphyrin dyes for DSSC.
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sensitized solar cells with high open circuit voltage performance. J Mater Chem
Shengzhong Li: Synthesized and characterized the dyes, Writing-
original draft. Shuangyu Zhang: Device fabrication and performance
measurement. Shu Mei: Data curation. Xiangfei Kong: Investigation.
Miao Yang: Formal analysis, Writing-review. Wenjun Wu: Device
studies, Formal analysis, Data curation. Shuhua Zhang: DFT Calcula-
tion, Formal analysis. Haijun Tan: Conceptualization, Supervision,
Funding acquisition, Writing-review & editing.
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Dibenzoylmethanato)boron difluoride derivatives containing triphenylamine
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15] Tang Y, Wang Y, Li X, Agren H, Zhu WH, Xie Y. Porphyrins containing a
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Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
4
829–36.
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17] Luo C, Bi W, Deng S, Zhang J, Chen S, Li B, et al. Indolo[3, 2, 1-jk]carbazole
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Acknowledgements
This work was supported by grants from the National Natural Science
Foundation of China (NSFC 21663010), Natural Science Foundation of
Guangxi, China (2015GXNSFBA139029), the special funding for
distinguished experts from Guangxi Zhuang Autonomous Region.
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21] Funabiki K, Mase H, Hibino A, Tanaka N, Mizuhata Sakuragi. Synthesis of a novel
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Appendix A. Supplementary data
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186–92.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2021.109308.
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22] Tang J, Wu W, Hua J, Li J, Li X, Tian H. Starburst triphenylamine-based cyanine
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