Comparative analysis of triarylamine and phenothiazine sensitizer donor units in dye-sensitized solar cells

Article abstract of DOI:10.1039/c6cc09178d

A homologous set of dyes that differ only in the donor fragments, namely phenothiazine (PTZ) and triarylamine (TPA) units, were evaluated in dye-sensitized solar cells (DSSCs). The novel PTZ-based dye differs from the TPA-based dye in that it contains a sulfur bridge that planarizes two aromatic rings and enables higher dye loading and higher stability in the oxidized form. These positive features notwithstanding, the superior absorptivity of devices sensitized by TPA-based dyes resulted in significantly higher power conversion efficiencies (PCEs) than those sensitized by PTZ-based dyes.

Full text of DOI:10.1039/c6cc09178d

ChemComm
View Article Online
View Journal
COMMUNICATION
Comparative analysis of triarylamine and
phenothiazine sensitizer donor units
Cite this:DOI: 10.1039/c6cc09178d
in dye-sensitized solar cells†
Received 17th November 2016,
Accepted 20th January 2017
Valerie A. Chiykowski, Brian Lam, Chuan Du and Curtis P. Berlinguette*
DOI: 10.1039/c6cc09178d
rsc.li/chemcomm
A homologous set of dyes that differ only in the donor fragments,
Given the long-standing interest of our program in developing
namely phenothiazine (PTZ) and triarylamine (TPA) units, were robust dyestuffs,8,37–40 we set out to better understand the under-
evaluated in dye-sensitized solar cells (DSSCs). The novel PTZ-based lying chemistry of dyes containing the PTZ units by contrasting it
dye differs from the TPA-based dye in that it contains a sulfur bridge with the more established TPA unit. We compare herein the
that planarizes two aromatic rings and enables higher dye loading performance of the novel dye (E)-2-cyano-3-(5-(4-(3,7-dimethoxy-
and higher stability in the oxidized form. These positive features 10H-phenothiazin-10-yl)phenyl)thiophen-2-yl)acrylic acid (PTZ)
notwithstanding, the superior absorptivity of devices sensitized by with the structurally related compound (E)-3-(5-(4-(bis(4-methoxy-
TPA-based dyes resulted in significantly higher power conversion phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid41 (TPA)
efficiencies (PCEs) than those sensitized by PTZ-based dyes.
in DSSCs (Fig. 1). There are literature precedents for dyes bearing
the PTZ unit in DSSCs,42–44 and these studies have shown that
There are four key classes of light harvesting materials that have linking the p-bridge to the para-carbon of the PTZ unit increases
proven to be effective in dye-sensitized solar cells1,2 (DSSCs): dye aggregation and undesirable charge recombination relative
quantum dots,3–5 ruthenium complexes,1,6–10 porphyrins,11–15 and to dyes where the p-bridge is linked to the PTZ through the
metal-free ‘‘donor–p-bridge–acceptor’’ (D–p–A) molecules.16–22 An nitrogen atom (Scheme S1, ESI†).45,46 We therefore confined this
appealing aspect of the latter class of dyes is the potential to study to the analysis of PTZ through the nitrogen atom. The
circumvent the need for rare or toxic metals. However, state-of-the- p-bridge was selected on the basis that thiophene is widely used
art organic dyes currently produce power conversion efficiencies in organic dyes and has been shown to broaden the absorption
(PCEs) that are often below 10%, with few exceptions,23,24 and thus envelope of chromophores.17,47,48 The structure–property analysis
further advances are needed.2
detailed herein shows that the sulfur tether of PTZ leads to higher
The triphenylamine (TPA) motif is one of the most extensively stability in the oxidized form, which is proven through direct
studied donor units in D–p–A dyes owing to its broad spectral comparisons of PTZ and TPA both in solution (electrochemically)
absorption and electrochemical stability in the oxidized form.25–33 and immobilized on TiO2 (spectroelectrochemically). PTZ exhibits
Indeed, organic dyes bearing the TPA unit produce some of the much higher dye-loading relative to TPA, but these features do not
highest PCEs of organic chromophores reported to date in DSSCs.16 compensate for the blue-shifted absorption of PTZ that precludes
Phenothiazine (PTZ) is structurally analogous to the TPA unit, with the generation of meaningful photocurrents.
the exception of a sulfur bridge that links two phenyl rings. This
The novel dye PTZ was synthesized in accordance with
bridge serves to increase the planarity of the two aromatic rings and related procedures (Fig. S1, ESI†).47,49,50 The PTZ unit, P1,
therefore imparts a starkly different electronic structure relative to was accessed through an Ullmann condensation of two primary
the TPA unit.34 One key outcome of planarizing the aromatic rings amines prior to the addition of the sulfur-bridge to form P2.
is a higher redox stability in the oxidized form due to delocalization
of p-electrons,35 a feature that has been used effectively to avoid
over-charging in lithium-ion batteries.36
Departments of Chemistry and Chemical & Biological Engineering, The University of
British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1, Canada.
E-mail: cberling@chem.ubc.ca
† Electronic supplementary information (ESI) available: Experimental procedures,
1H and 13C NMR spectra, mass spectra, dye-loading studies, and spectroscopic and
Fig. 1 Molecular structures of the TPA and PTZ dyes investigated here.
time-dependent DFT data. See DOI: 10.1039/c6cc09178d
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
Table 1 Summary of spectroscopic and electrochemical properties for
TPA and PTZ dyes
A brominated phenyl ring was added to P2 to yield the tertiary
amine P3 by an Ullmann condensation catalyzed by copper
powder. A palladium-catalyzed Suzuki coupling was used to
isolate P4 prior to addition of the cyanoacrylic acid anchoring
group by a Knoevenagel condensation to yield the PTZ dye. The
E(S+/S*)e
a
b
c
d
lmax
lFluor
E1/2
E0–0
Dye
(nm)
(nm)
(V vs. NHE)
(eV)
(V vs. NHE)
TPA
501 (2.8)
411 (1.3)
531
572
0.97
0.78
2.23
2.56
À1.26
À1.78
TPA dye was synthesized using previously reported literature PTZ
procedures.41 The intermediate products and final dyes were
a
Corresponds to the maximum wavelength of the lowest-energy
1
structurally characterized by H and 13C NMR spectroscopies,
as well as high-resolution mass spectrometry (see the ESI†).
Density functional theory (DFT) was used to compare the
geometries and electronic structures of PTZ and TPA. This analysis
confirmed that the sulfur bridge of PTZ holds the phenothiazine
donor unit perpendicular to the p-bridge, thereby disrupting the
conjugation of the highest occupied molecular orbital (HOMO) on
the donor unit and the lowest unoccupied molecular orbital
(LUMO) that is localized to the cyanoacrylic acid. The coplanarity
of the p-bridge with the pinwheel orientation of the TPA groups for
TPA yields a HOMO delocalized over the donor, acceptor and
bridge portions of the molecule (Fig. 2a). These differences
in orbital overlap help explain the much higher extinction
coefficients recorded for TPA (e = 2.8 Â 104 MÀ1 cmÀ1) relative
to PTZ (e = 1.4 Â 104 MÀ1 cmÀ1) recorded in solution UV-visible
absorption experiments (Fig. 2b and Table 1). The restricted
geometry of PTZ also leads to a forbidden HOMO - LUMO
transition that is expected at 760 nm but is not experimentally
observed. The lowest energy band, with a maximum at 411 nm,
for PTZ instead corresponds to a higher energy HOMOÀ3 -
LUMO transition (Fig. S4, ESI†).
absorption band; e in units of 104 MÀ1 sÀ1 indicated in parentheses.
b
Maximum wavelength of the emission band after excitation at lmax
.
c
+
TPAꢀ /TPA0 and PTZꢀ+/PTZ0 redox couples in 0.1 M n-NBu4PF6 electro-
lyte solution at 50 mV sÀ1 and referenced against Ag/AgCl in saturated
d
KCl solutions (+197 mV vs. NHE). E0-0 determined from intersection
e
of normalized absorption and emission spectra. Calculated using the
relationship: E(S+/S*) = E1/2 À E0–0
.
Fig. 3 (a) Cyclic voltammograms for TPA and PTZ recorded in 0.1 M
n-NBu4PF6 MeCN solutions at room temperature. (b) Temporal change in
UV-vis absorption at 748 and 625 nm for the one-electron oxidized forms
of TPA and PTZ, respectively, immobilized on TiO2. The dyes were each
oxidized by applying a bias E1/2 +100 mV for 1 min in 0.1 mM n-NBu4PF6 in
MeCN. The first data points (i.e., t = 0 s) correspond to the data recorded
after the applied bias was removed. Dashed lines indicate t1/2
.
Cyclic voltammograms recorded for each dye in MeCN
solution revealed that the dye+/dye redox potentials are at +0.78
and +0.97 V vs. NHE for PTZ and TPA, respectively (Fig. 3a and the dye cation (TPA+ or PTZ+). The decay of the absorption band
Table 1). The reduction potential for PTZ is positively shifted due intensity as a function of time was measured following the removal
to the electron-rich sulfur tether increasing the planarity and of the applied bias (Fig. 3b). The PTZ+ persisted the longest in the
conjugation throughout the PTZ unit, thereby stabilizing the oxidized form with a half-life (t1/2) of 10 min, while the t1/2 for TPA+
oxidized form of the dye. The E1/2 value for PTZ is near the was merely 3.5 min. These results supported our hypothesis that
threshold for regeneration by iodide (the redox potential for PTZ+ would exhibit greater oxidative stability.
the I2 À/IÀ couple is +0.8 V vs. NHE8,51) which can potentially
stunt dye regeneration (vide infra), but efficient dyes with similar desorption of the respective sensitized TiO2 substrates in basic
potentials are known.52
media and subsequent spectrophotometric quantification. The
The dye loadings for each of the dyes were determined by
ꢀ
The stabilities of both dyes in the oxidized form were analyzed PTZ dye exhibited approximately twice the dye loading coverage
by spectroelectrochemical techniques. The working electrode (i.e., than TPA (Table S1, ESI†). This stark difference is attributed to
TPA or PTZ adsorbed to TiO2) was held at a potential +100 mV the smaller molecular volume occupied by the tethered donor
greater than the sensitizer redox potential for 1 min, a time period unit on PTZ. Higher dye loading for PTZ relative to TPA was also
that yielded long-wavelength absorption maxima corresponding to observed when co-adsorbed with chenodeoxycholic acid (CDCA)
coabsorbent, and thus we conclude that higher concentrations
of PTZ on TiO2 are not merely due to dye aggregation.
The two dyes were evaluated in the DSSC with an iodine-based
electrolyte system and platinized counter electrode (Table 2). The
current–voltage profiles and the corresponding metrics are provided
in Fig. 4. The short-circuit current density ( Jsc, 13.3 mA cmÀ2
)
measured for TPA was significantly higher than that measured for
PTZ (8.2 mA cmÀ2) with CDCA. This stark difference can be
rationalized by the much broader absorption envelope for TPA
relative to PTZ, but we cannot rule out that the HOMO of the
PTZ dye as too high in energy to be regenerated by IÀ.2,8,39,53 The
open-circuit potential, Voc, is also higher for TPA, presumably
Fig. 2 (a) Calculated frontier orbitals of optimized structures for TPA and
PTZ dyes plotted at an absolute isovalue of 0.05; and (b) UV-visible
absorption spectra for TPA and PTZ dyes recorded in MeCN.
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017

View Article Online
ChemComm
Communication
Table 2 Dye-sensitized solar cell performance under 1.5 AM (1 sun)
illumination for TPA and PTZ
Notes and references
¨
1 B. O’Regan and M. Gratzel, Nature, 1991, 353, 737.
Jsc (mA cmÀ2
12.3 Æ 0.5
)
Voc (mV)
Fill factor (FF) Z (%)
2 A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson, Chem.
Rev., 2010, 110, 6595–6663.
Dye
TPA
0.760 Æ 0.003 0.76 Æ 0.01
0.781 Æ 0.003 0.72 Æ 0.02
0.709 Æ 0.003 0.73 Æ 0.01
0.745 Æ 0.001 0.75 Æ 0.01
6.28 Æ 0.87
7.14 Æ 0.12
3.90 Æ 0.04
5.57 Æ 0.02
¨
3 M. Gratzel, Inorg. Chem., 2005, 44, 6841–6851.
TPA+CDCA 13.3 Æ 0.2
4 P. K. Santra and P. V. Kamat, J. Am. Chem. Soc., 2012, 134, 2508–2511.
5 R. Wang, Y. Shang, P. Kanjanaboos, W. Zhou, Z. Ning and E. H. Sargent,
Energy Environ. Sci., 2016, 1–14.
6 M. K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, N. Vlachopoulos,
M. Graetzel and P. Liska, J. Am. Chem. Soc., 1993, 115, 6382–6390.
PTZ
7.9 Æ 0.1
PTZ+CDCA 8.2 Æ 0.1
The I3À/IÀ electrolyte solution composed of 1.0 M DMII, 60 mM I2,
0.5 M tert-butylpyridine, 0.05 M NaI and 0.1 M GuNCS in a mixed
solvent system of acetonitrile and valeronitrile (85 : 15; v/v). Dye solution
contains 0.25 mM dye and 0.25 mM CDCA. Data correspond to average
cell values with standard deviations derived from no fewer than three
cells.
´
¨
7 M. K. Nazeeruddin, P. Pechy and M. Gratzel, Chem. Commun., 1997,
1705–1706.
8 P. G. Bomben, K. C. D. Robson, B. D. Koivisto and C. P. Berlinguette,
Coord. Chem. Rev., 2012, 256, 1438–1450.
9 F. Gao, Y. Wang, J. Zhang, D. Shi, M. Wang, R. Humphry-Baker, P. Wang,
¨
S. M. Zakeeruddin and M. Gratzel, Chem. Commun., 2008, 2635.
10 S. Ito, N.-L. C. Ha, G. Rothenberger, P. Liska, P. Comte, S. M. Zakeeruddin,
´
¨
P. Pechy, M. K. Nazeeruddin and M. Gratzel, Chem. Commun., 2006,
4004–4006.
11 S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B. F. E. Curchod,
N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin
¨
and M. Gratzel, Nat. Chem., 2014, 6, 242–247.
12 Y. Xie, Y. Tang, W. Wu, Y. Wang, J. Liu, X. Li, H. Tian and W.-H. Zhu,
J. Am. Chem. Soc., 2015, 137, 14055–14058.
13 C. Y. Lee, C. She, N. C. Jeong and J. T. Hupp, Chem. Commun., 2010,
46, 6090.
14 W. M. Campbell, A. K. Burrell, D. L. Officer and K. W. Jolley, Coord.
Chem. Rev., 2004, 248, 1363–1379.
15 A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran,
M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin
Fig. 4 Current–voltage curves for DSSCs with the indicated sensitizers
under 1.5 AM illumination using an I3À/IÀ redox mediator.
¨
and M. Gratzel, Science, 2011, 334, 629–634.
16 W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan
and P. Wang, Chem. Mater., 2010, 22, 1915–1925.
17 D. P. Hagberg, T. Marinado, K. M. Karlsson, K. Nonomura, P. Qin,
G. Boschloo, T. Brinck, A. Hagfeldt and L. Sun, J. Org. Chem., 2007,
72, 9550–9556.
18 K. C. D. Robson, K. Hu, G. J. Meyer and C. P. Berlinguette, J. Am.
Chem. Soc., 2013, 135, 1961–1971.
because of the higher concentration of minority carriers in TiO2
in the case of the TPA dye. The lower energy of the TPA HOMO
level is also expected to facilitate faster regeneration of the oxidized
dye, which can also improve the measured photovoltages.18,54–56
A
difference in recombination with the oxidized electrolyte species
(I3À) does not appear to be responsible for the differences in
voltages because the more highly loaded PTZ molecules on the
TiO2 surface would be expected to increase the photovoltage,
which is not observed here. Preliminary stability studies were
carried out by subjecting cells containing TPA and PTZ to constant
illumination at AM 1.5 (1 Sun) and 45 1C for 150 h in a light-
soaking chamber and periodically collecting Voc measurements
(Fig. S5, ESI†). TPA shows a slightly faster rate of performance
decline with 87% of initial Voc after 150 h of light-soaking. PTZ
maintained 91% of the open-circuit potential over the same
period. Now that PTZ has been identified as a redox stable
organic dye, further studies on how this stability translates into
cell stability under illumination and high temperatures will be
carried out.57
We investigated the PTZ donor unit in a DSSC and bench-
marked it against the more widely used TPA donor unit using a
novel PTZ dye molecule. The planar PTZ geometry enables
higher dye coverage and higher stability in the oxidized form
relative to TPA. The stabilities of the two analogous N-linked
dyes were compared for the first time, herein, using spectro-
electrochemistry. However, the N-linked PTZ dyes are not
ideal sensitizers because the TPA unit has a higher optical
cross section and absorbs light at longer wavelengths. The
nominal thermodynamic driving force for dye regeneration by
IÀ also needs to be considered when evaluating dyes with this
PTZ unit.
19 K. Hu, K. C. D. Robson, C. P. Berlinguette and G. J. Meyer, Thin Solid
Films, 2014, 560, 49–54.
20 N. Zhou, K. Prabakaran, B. Lee, S. H. Chang, B. Harutyunyan,
P. Guo, M. R. Butler, A. Timalsina, M. J. Bedzyk, M. A. Ratner,
S. Vegiraju, S. Yau, C.-G. Wu, R. P. H. Chang, A. Facchetti, M.-C. Chen
and T. J. Marks, J. Am. Chem. Soc., 2015, 137, 4414–4423.
21 D. Zhou, Q. Yu, N. Cai, Y. Bai, Y. Wang and P. Wang, Energy Environ.
Sci., 2011, 4, 2030.
22 D.-Y. Chen, Y.-Y. Hsu, H.-C. Hsu, B.-S. Chen, Y.-T. Lee, H. Fu,
M.-W. Chung, S.-H. Liu, H.-C. Chen, Y. Chi and P.-T. Chou, Chem.
Commun., 2010, 46, 5256.
23 W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan
and P. Wang, Chem. Mater., 2010, 22, 1915–1925.
24 Z. Yao, M. Zhang, H. Wu, L. Yang, R. Li and P. Wang, J. Am. Chem.
Soc., 2015, 137, 3799–3802.
25 M. Liang and J. Chen, Chem. Soc. Rev., 2013, 42, 3453.
26 S. J. C. Simon, F. G. L. Parlane, W. B. Swords, C. W. Kellett, C. Du,
B. Lam, R. K. Dean, K. Hu, G. J. Meyer and C. P. Berlinguette, J. Am.
Chem. Soc., 2016, 138, 10406–10409.
27 K. Hu, K. C. D. Robson, E. E. Beauvilliers, E. Schott, X. Zarate,
R. Arratia-Perez, C. P. Berlinguette and G. J. Meyer, J. Am. Chem. Soc.,
2014, 136, 1034–1046.
28 C. S. Karthikeyan, H. Wietasch and M. Thelakkat, Adv. Mater., 2007,
19, 1091–1095.
29 H. J. Snaith, C. S. Karthikeyan, A. Petrozza, J. Teuscher, J.-E. Moser,
¨
M. K. Nazeeruddin, M. Thelakkat and M. Gratzel, J. Phys. Chem. C,
2008, 112, 7562–7566.
30 K. Willinger, K. Fischer, R. Kisselev and M. Thelakkat, J. Mater.
Chem., 2009, 19, 5364.
31 K. C. D. Robson, B. D. Koivisto and C. P. Berlinguette, Inorg. Chem.,
2012, 51, 1501–1507.
32 K. C. D. Robson, B. Sporinova, B. D. Koivisto, E. Schott, D. G. Brown
and C. P. Berlinguette, Inorg. Chem., 2011, 50, 6019–6028.
33 K. Hu, A. D. Blair, E. J. Piechota, P. A. Schauer, R. N. Sampaio, F. G. L.
Parlane, G. J. Meyer and C. P. Berlinguette, Nat. Chem., 2016, 8, 853–859.
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
34 R. K. Konidena, K. R. J. Thomas, S. Kumar, Y.-C. Wang, C.-J. Li and 46 A. S. Hart, C. B. K C, N. K. Subbaiyan, P. A. Karr and F. D’Souza, ACS
J.-H. Jou, J. Org. Chem., 2015, 80, 5812–5823. Appl. Mater. Interfaces, 2012, 4, 5813–5820.
35 W. Zhu, Y. Wu, S. Wang, W. Li, X. Li, J. Chen, Z.-S. Wang and 47 C. Bonnier, D. D. Machin, O. K. Abdi, K. C. D. Robson and
H. Tian, Adv. Funct. Mater., 2010, 21, 756–763. B. D. Koivisto, Org. Biomol. Chem., 2013, 11, 7011.
36 S. Ergun, C. F. Elliott, A. P. Kaur, S. R. Parkin and S. A. Odom, Chem. 48 K. C. D. Robson, B. D. Koivisto, T. J. Gordon, T. Baumgartner and
Commun., 2014, 50, 5339–5341. C. P. Berlinguette, Inorg. Chem., 2010, 49, 5335–5337.
37 G. Li, P. G. Bomben, K. C. D. Robson, S. I. Gorelsky, C. P. Berlinguette 49 M. V. Jovanovic and E. R. Biehl, J. Org. Chem., 1984, 49, 1905–1908.
and M. Shatruk, Chem. Commun., 2012, 48, 8790.
38 G. Li, K. Hu, K. C. D. Robson, S. I. Gorelsky, G. J. Meyer, C. P. Berlinguette
and M. Shatruk, Chem. – Eur. J., 2014, 21, 2173–2181.
50 S.-H. Lee, C. T.-L. Chan, K. M.-C. Wong, W. H. Lam, W.-M. Kwok and
V. W.-W. Yam, J. Am. Chem. Soc., 2014, 136, 10041–10052.
51 G. Boschloo and A. Hagfeldt, Acc. Chem. Res., 2009, 42, 1819–1826.
39 K. C. D. Robson, P. G. Bomben and C. P. Berlinguette, Dalton Trans., 52 F. M. Jradi, X. Kang, D. O’Neil, G. Pajares, Y. A. Getmanenko,
2012, 41, 7814.
P. Szymanski, T. C. Parker, M. A. El-Sayed and S. R. Marder, Chem.
Mater., 2015, 27, 2480–2487.
53 S. Tatay, S. A. Haque, B. O’Regan, J. R. Durrant, W. J. H. Verhees,
40 P. G. Bomben, K. C. D. Robson, P. A. Sedach and C. P. Berlinguette,
Inorg. Chem., 2009, 48, 9631–9643.
˜
41 Q.-Y. Yu, J.-Y. Liao, S.-M. Zhou, Y. Shen, J.-M. Liu, D.-B. Kuang and
C.-Y. Su, J. Phys. Chem. C, 2011, 115, 22002–22008.
J. M. Kroon, A. Vidal-Ferran, P. Gavina and E. Palomares, J. Mater.
Chem., 2007, 17, 3037–3044.
42 Z. Iqbal, W.-Q. Wu, Z.-S. Huang, L. Wang, D.-B. Kuang, H. Meier and 54 F. Li, J. R. Jennings and Q. Wang, ACS Nano, 2013, 7, 8233–8242.
D. Cao, Dyes Pigm., 2016, 124, 63–71.
43 Z.-S. Huang, H. Meier and D. Cao, J. Mater. Chem. C, 2016, 4,
55 J. R. Jennings, Y. Liu and Q. Wang, J. Phys. Chem. C, 2011, 115,
15109–15120.
2404–2426.
56 W. B. Swords, S. J. C. Simon, F. G. L. Parlane, R. K. Dean, C. W.
Kellett, K. Hu, G. J. Meyer and C. P. Berlinguette, Angew. Chem.,
2016, 128, 6060–6064.
44 J.-S. Luo, Z.-Q. Wan and C.-Y. Jia, Chin. Chem. Lett., 2016, 27,
1304–1318.
45 H.-H. Gao, X. Qian, W.-Y. Chang, S.-S. Wang, Y.-Z. Zhu and 57 V. A. Chiykowski, B. Lam, C. Du and C. P. Berlinguette, Chem.
J.-Y. Zheng, J. Power Sources, 2016, 307, 866–874.
Commun., 2016, DOI: 10.1039/c6cc09992k.
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017