Superior Light-Harvesting Heteroleptic Ruthenium(II

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Superior Light-Harvesting Heteroleptic Ruthenium (II) Complexes with Electron-Donating Antennas for High Performance Dye-Sensitized Solar Cells Wangchao Chen, Fantai Kong, Zhao-Qian Li, Jia Hong Pan, Xuepeng Liu, Fuling Guo, Li Zhou, Yang Huang, Ting Yu, and Songyuan Dai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b04411 • Publication Date (Web): 13 Jul 2016 Downloaded from http://pubs.acs.org on July 14, 2016

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ACS Applied Materials & Interfaces

Superior Light-Harvesting Heteroleptic Ruthenium (II) Complexes with

Electron-Donating

Antennas

for

High

Performance

Dye-Sensitized Solar Cells

Wang-Chao Chen,a,b Fan-Tai Kong,*,a Zhao-Qian Li,a Jia-Hong Pan,*,c Xue-Peng Liu,a,b Fu-Ling Guo,a Li Zhou,a Yang Huang,a Ting Yu,a,b and Song-Yuan Dai*,c,a

a

Key Laboratory of Novel Thin Film Solar Cells, Institute of Applied Technology, Hefei Institutes

of Physical Science, Chinese Academy of Sciences, Hefei, 230031, P. R. China b

University of Science and Technology of China, Hefei, 230026, P. R. China

c

Beijing Key Laboratory of Novel Thin Film Solar Cells, North China Electric Power University,

Beijing, 102206, P. R. China

ABSTRACT: Three heteroleptic polypyridyl ruthenium complexes, RC-41, RC-42, and RC-43, with efficient electron-donating antennas in the ancillary ligands were designed, synthesized and characterized as sensitizers for dye-sensitized solar cell. All the RC dye sensitizers showed remarkable light-harvesting capacity and broadened absorption range. Significantly, RC-43 obtained the lower energy metal-ligand charge transfer (MLCT) band peaked at 557 nm with a high molar extinction coefficient of 27 400 M-1 cm-1. In conjunction with TiO2 photoanode of sub-microspheres and iodide-based electrolytes, the DSSCs sensitizing with the RC sensitizers, achieved impressively high short-circuit current density (19.04 mA cm-2 for RC-41, 19.83 mA cm-2 for RC-42, and 20.21 mA cm-2 for RC-43) and power conversion efficiency

1

ACS Paragon Plus Environment


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(10.07% for RC-41, 10.52% for RC-42, and 10.78% for RC-43). The superior performances of RC dye sensitizers were attributed to the enhanced light-harvesting capacity and incident-photon-to-current efficiency (IPCE) caused by the introduction of electron-donating antennas in the ancillary ligands. The interfacial charge recombination/regeneration kinetics and electron lifetime were further evaluated by the electrochemical impedance spectroscopy (EIS) and transient absorption spectroscopy (TAS). These data decisively revealed the dependences on the photovoltaic performance of ruthenium sensitizers incorporating electron-donating antennas.

KEYWORDS: ruthenium sensitizers, electron-donating antennas, light-harvesting, high-efficiency, dye-sensitized solar cells.

1. INTRODUCTION Dye-sensitized solar cells (DSSCs), in which attached dyes sensitize wide-band gap semiconductor, have been intensively studied in recent decades.1-2 In the DSSCs, the dye sensitizer molecules on the surface of metal oxide semiconductor dominate the yield of light-harvesting, separated charges and the photon to current conversion efficiency. A series of dye sensitizer molecules, such as zinc porphyrin dyes3-4 and metal-free organic dyes5-6 have been developed in recent years, whereas ruthenium complex sensitizers7-10 remain the most widely investigated and used due to the broad absorption spectrum,11 high conversion efficiency,12 appropriate energy levels,13-14 2


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and excellent stability.15 The DSSCs based on ruthenium complexes (N719,9 Z907,16 C106,17 and CYC-B1118) have achieved photoelectric conversion efficiencies over 10% under AM 1.5 sunlight illumination (100 mW cm-2) and the highest value of being 12.3%.19 Incorporating electron delocalization donating antenna or hole transport chromophore into a ruthenium polypyridyl complex sensitizer is an advisable approach to increasing the light-harvesting efficiency in MLCT band and red-shifting the absorption spectrum of ruthenium sensitizer. Besides, the introduction of electron-donating antenna can also shift the positive hole on the polypyridyl ligands by intramolecular charge-transfer, and thus debasing the rate of electron recombination between the dye and metal oxide semiconductor surface.14 According to these evidences, some heteroleptic ruthenium polypyridyl sensitizers featuring electron-donating antennas, such as carbazole,20 phenothiazines (PTZ),21 and triphenylamine (TPA)22 have been designed, synthesized and applied to DSSCs. All these dye sensitizers showed good light-harvesting capacities and satisfactory conversion efficiency up to 10% under 1 sun irradiation condition. Based on the aforementioned argument, here we present an investigation on the synthesis, photophysical, electrochemical properties, and solar cell performances of three meticulously designed ruthenium complex sensitizers, coded as RC-41, RC-42 and RC-43

(see

Scheme

1).

All

dyes

RC

comprise

thiocyanato

ligands,

4,4'-dicarboxy-2,2'-bipyridine ligand (acts as the anchoring or electron acceptor group), and strong electron-donating antenna (acts as the electron donating group). 3



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Scheme 1. Molecular Structures of Z907, RC-41, RC-42, and RC-43 Sensitizers

For for the RC-41 dye, phenylcarbazol, a new electron-donating antenna which has similar structure with TPA, is introduced into the bipyridine ligand. In the structure

of

RC-42

dye,

a

stronger

electron-donating

antenna-methoxy-triphenylamine (MeO-TPA) is attached to the bipyridine ligand.23 To further improve the electron donating ability and extend conjugation length of the ancillary bipyridine ligand in RC-42 dye, ethylene-dioxythiophene (EDOT)24,25 is employed as the spacer between the MeO-TPA and bipyridine unit in the case of RC-43 dye. In order to evaluate the photophysical, electrochemical and photovoltaic properties for the novel RC dye sensitizers, Z907,16 which contains long alkyl chains as electron-donating moieties, is used as a benchmark dye through this work. Besides, taking into account the long and bulky electron-donating antennas on the bipyridine, a larger special surface area of TiO2 photoanode should be employed to avoid the serious steric hindrance and interfacial charge recombination. Therefore, in this work, the mesoporous TiO2 microspheres with superior surface area were used as the photoanode material in the DSSC devices instead of the conventional TiO2 4


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nanoparticles.26

2. RESULTS AND DISCUSSION

Synthesis of Ruthenium Sensitizers

Scheme 2. Synthetic Routes for RC Dye Sensitizers

Three heteroleptic ruthenium complexes coded as RC-41, RC-42, and RC-43, which incorporated strong electron-donating antenna substituted bipyridine as the ancillary ligands, were synthesized with a cautious synthetic protocol (shown in Scheme 2). The electron-donating ancillary ligands were obtained from the corresponding boronic acid or boric acid ester with 4,4'-dibromo-2,2'-bipyridine by typical Suzuki coupling reaction. The ruthenium heteroleptic polypyridyl complex was synthesized via the typical one-pot synthetic procedure, then purified through the Sephadex LH-20 column to get the highly pure product. The detailed synthetic route and identification for these dyes with 1H NMR and MALDI-TOF-MS are described in the Supporting Information, which are found to be in good agreement with their structures. 5



Photophysical and Electrochemical Properties of Ruthenium Sensitizers. 3.0

a

RC-41 RC-42 RC-43 Z907

6

Absorption (a.u.)

8

ε (104 M-1 cm-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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4

2

2.5

RC-41 RC-42 RC-43 Z907

b

2.0 1.5 1.0 0.5 0.0

0 400

500

600

700

500

800

600

700

800

Wavelength (nm)

Wavelength (nm)

Figure 1. (a) Electronic absorption spectra of the RC-41, RC-42, RC-43, and Z907 sensitizers in DMF. (b) Electronic absorption spectra of the RC-41, RC-42, RC-43, and Z907 anchored on a TiO2 sub-microspheres thin film (7.5 µm).

The UV-vis absorption spectra of RC-41, RC-42, RC-43, and Z907 in DMF solution are shown in Figure 1a, and the detailed optical data are collected in Table 1. The absorption bands were observed at 371 nm, 404 nm, and 418 nm for RC-41, RC-42, and RC-43 sensitizer, respectively, which can be attributed to the intra-ligand π-π* charge transfer (ILCT) transition of the conjugated bipyridine ligand and high-energy metal-to-ligand charge transfer (MLCT) transition.30 Apart from RC-41 (371 nm), the absorption bands of other two RC sensitizers (404 nm and 418 nm) were obviously red-shifted compared with the benchmark Z907 sensitizer (372 nm). Moreover, all these bands of RC sensitizers obtained apparently increasing molar absorption coefficients (42 870 M-1 cm-1 for RC-41, 48 160 M-1 cm-1 for RC-42, and 64 280 M-1 cm-1 for RC-43) compared with Z907 (11 900 M-1 cm-1), which could be ascribed to 6


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the introduction of the strong electron-donating antennas into the bipyridine ligand. The characteristic lower-energy MLCT absorption bands around 540nm (537 nm for RC-41, 542 nm for RC-42, and 557 nm for RC-43), which were ascribed to the charge transfer from the metal center to the 4,4'-dicarboxy-2,2'-bipyridine ligand, and played an crucial role on the performance of the devices.30 All the low-energy MLCT absorption bands of RC sensitizers were bathochromic-shift compared with that of Z907 (520 nm), suggesting a shrinked band gap of MLCT transition which was beneficial for light-harvesting. The molar extinction coefficients (ε) of the low-energy MLCT absorption bands for RC-41, RC-42, and RC-43 were 19 570 M-1 cm-1, 21 070 M-1 cm-1, and 27 400 M-1 cm-1, which were significantly higher than that of Z907 (12 500 M-1 cm-1). The red shift of MLCT bands and enhanced molar extinction coefficient can be ascribed to the incorporation of electron-donating moieties.31 In comparison of RC-41, the red-shifted MLCT bands for RC-42 and RC-43 could be attributed to the more powerful electron-donating ability of MeO-TPA. Furthermore, the excellent absorption bands for RC-43 compared to RC-42 uncovered the superduper impact from the modified moiety of EDOT.25 Consideration of the consistent surface area being drafted by dyes with diverse light-harvesting efficiency, RC dyes with high molar extinction coefficient allow to higher light harvesting yield, and ultimately, a noteworthy reduction in film thickness in the future. Figure 1b shows the absorption spectra of RC sensitizers adsorbed on TiO2 thin films. When RC sensitizers were anchored on transparent TiO2 thin films, the absorption spectra had similar patterns with those in DMF solution. However, the 7



absorption spectra on the TiO2 electrode were broader and slightly blue-shifted for the low-energy MLCT compared with those in solution. The shift to higher energy can be ascribed to the destabilization in the energy levels of the ground and excited states of the sensitizers on the TiO2 thin films compared with that in DMF solution, resulting from the deprotonation of carboxylic groups in the dye self-assembly process or the interaction of anchoring groups to the TiO2 film.8 The broadened MLCT bands are favorable for harvesting more photons across the solar spectrum, which may generates more substantial photocurrent.14

10 8 -6

Current (10 A)

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a

RC-41 RC-42 RC-43

6 4 2 0 -2 0.4

0.6

0.8

1.0

1.2

Potential (V vs. SCE)

Figure 2. (a) Cyclic voltammetry curves of RC-41, RC-42, and RC-43 with 0.1 M (n-C4H9)4NPF6 DMF solution. (b) The schematic energy levels of RC-41, RC-42, and RC-43.

Table 1. Photophysical and Electrochemical Properties of Sensitizers

Sensitizer

λmax a[nm](ε/ M−1 cm−1)

RC-41

371(42 870) 537(19 570)

0

E

b S+/S

0.76

[V]

E0−0 c[eV] 1.94

8


0

E

d S+/S*

[V]

-1.18

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a

RC-42

404(48 160) 542(21 070)

0.86

1.85

-0.99

RC-43

418(64 280) 557(27 400)

0.90

1.74

-0.84

Z907

372(11 900) 525(12 500)

0.78e

2.17e

-1.39e

Measured in DMF (2 × 10-5 M) at room temperature. bRecorded in DMF/0.1 M TBAP, GC working and Pt

counter electrodes, scan rate = 50 mV s-1 and SCE as the reference electrode, potentials measured vs SCE were converted to normal hydrogen electrode (NHE) cEstimated from the intersection between the absorption and 0

emission spectra in DMF. dCalculated from E

S+/S

-E

0−0.

e

according to ref.33.

To investigated the molecular orbital energy levels of the RC sensitizers, the electrochemical characteristics of these RC dyes were obtained using the cyclic voltammetry (CV) method with a Ferrcene/Ferrocence+ couple as external reference (+0.63 V vs. NHE). The results are given in Figure 2 and Table 1. The cyclic voltammograms indicated that all sensitizers are redox-active, namely, Ru-centered

(oxidation)

and

ligand-centered

(reduction)

processes.

The

0

ground-oxidation potentials (E

S+/S,

corresponding to the HOMO level of sensitizers,

all vs. NHE) of the RC sensitizers (0.76 V for RC-41, 0.86 V for RC-42, and 0.90 V for RC-43) were all more positive than the I-/I3- redox couple potential (0.4 V vs. NHE)32 providing a thermodynamic driving force for dye regeneration efficiently. The 0

excited-state oxidation potentials (E

) corresponding to the LUMO energy levels

S+/S*

were -1.18 V, -0.99 V, and -0.84 V, respectively. The LUMO levels were more negative than the conduction-band potential of TiO2 (-0.5 V vs. NHE),32 indicating a sufficient driving force for electron injection from excited sensitizers to the conduction band of TiO2. Moreover, it should be noted that all RC sensitizers’ HOMO 9



levels are higher than that of Z907 which may be attributed to both the extended conjugation length or the nature of the heterocyclic system and delocalization of the HOMO by incorporation of different electron-donating antennas.14

Photovoltaic Device Characterizations. 100

a

20

15

RC-41 RC-42 RC-43 Z907

10

5

b

80

IPCE (%)

-2

Current Density (mA cm )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

RC-41 RC-42 RC-43 Z907

40 20 0

0 0

200

400

600

800

400

Voltage (mV)

500

600

700

800

Wavelength (nm)

Figure 3. (a) Current density-voltage characterization for photovoltaic devices under AM 1.5G full-sun intensity. (b) The IPCE spectra of DSSC devices.

Table 2. Photovoltaic Properties of DSSCs Measured under AM 1.5G One-Sun

JSC Sensitizer

VOC

η FF

[mA cm-2]

[mV]

RC-41

18.73

0.704

RC-42

19.47

RC-43 Z907

Dye loading

[%]

[10−7 mol cm−2]

0.73

9.62

1.8

0.710

0.73

10.09

1.6

20.06

0.706

0.74

10.48

1.5

17.11

0.746

0.72

9.13

2.2

Irradiation.

10


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The current density-voltage curves of the RC dye sensitizers along with Z907 are shown in Figure 3a. The detailed photovoltaic values for the photovoltaic parameters (short circuit photocurrent density (JSC), open circuit voltage (VOC), fill factor (FF), and power conversion efficiency (η) of all devices are illustrated in Table 2. Encouragingly, all the RC dyes showed remarkable performance under AM 1.5G one

sun

(100

mW·cm-2).

The

solar

cell

sensitized

by

RC-41

(with

phenylcarbazol-substituted ancillary ligand) obtained JSC of 18.73 mA cm-2, VOC of 0.704 V, and η of 9.62%. The device sensitized by RC-42 (with MeO-TPA-substituted ancillary ligand) exhibited JSC of 19.47 mA cm-2 and VOC of 0.710 V, yielding a PCE value of 10.09%. The stronger electron-donating capacity of MeO-TPA for RC-42 could be contributed to the better short-circuit current than phenylcarbazol moiety for RC-41. With MeO-TPA-EDOT-substituted ancillary ligand of RC-43, it gained the best performance in terms of JSC of 20.06 mA cm-2 and VOC of 0.706 V, leading to a PCE value of 10.48%. The significant increase in PCE value for RC-43- compared to RC-42-sensitized solar cells revealed the function of the EDOT moiety in the electron-donating antenna of the ruthenium sensitizer. Although the highest VOC of 0.746 V was obtained, the Z907-sensitized solar cells only got an inferior η of 9.13%, due to the obviously lower JSC of 17.11 mA cm-2 compared to that of RC dyes. The significant increase in JSC demonstrated that the incorporation of strong electron-donating antennas could achieve higher molar extinction coefficient, more efficient electron donation, and stronger hole-transport capacity which may led to higher η than Z907. 11



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To confirm the high generated photocurrent of the RC dyes, the incident photon-to-current conversion efficiency (IPCE) spectra of RC-41, RC-42, RC-43, and Z907-sensitized solar cells are measured. As shown in Figure 3b, for all RC dye sensitizers, in sympathy with the absorption spectra, the broader response regions and red-shifted threshold wavelengths were obtained appreciably than that of Z907. Furthermore, the IPCE of DSSC devices with RC-41, RC-42, and RC-43 as sensitizer showed remarkable IPCE value of about 90% in the plateau region. Significantly, the RC-43 dye sensitizer showed the most efficient sensitization of TiO2 thin film over the whole visible light range extending to 800 nm. Compared to RC-42 and RC-43, however, the RC-41 gained inferior IPCE values in the spectral region from 400 to 450 nm. It may be result from the relatively lower absorption coefficient during this region. As the benchmark dye, however, Z907-sensitized solar cell device obtains a relatively lower IPCE values. Besides, in some cases of conventional ruthenium dye,9,16 a decrease of the IPCE spectrum may be observed around 400 nm resulting from the competitive light absorption of I-/I3- in the electrolyte (just like the IPCE curve of Z907 in Figure 3b). Fortunately, there were still strong absorption band for the RC dyes with electron-donating antennas (42 870 M-1 cm-1 for RC-41, 48 160 M-1 cm-1 for RC-42, and 64 280 M-1 cm-1 for RC-43) at this wavelength. These absorption band could offset the competitive absorption from I-/I3- redox and remedy the gap in the IPCE spectrum. This phenomenon results from both strong photon harvesting capability of electron-donating antennas (the superior molar extinction coefficient of RC dyes) and the red shift in the absorption spectrum of RC dyes 12


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relative to Z907 dye. In summary, it can be concluded that the substitution of electron-donating moieties for long alkyl chains dramatically enhances the absorbed photon-to-current conversion efficiency and furthermore, the capacity to provide photon-generated current. Subsequently, dye desorption processes were measured by detaching the dyes from the TiO2 thin films using the solution consisting of tetrabutylammonium hydroxide (0.5 mL) and DMF (10 mL). The dye loading amounts of RC-41, RC-42, RC-43 and Z907 on TiO2 were 1.8 × 10−7, 1.7 × 10−7, 1.5 × 10−7, and 2.2 × 10−7 mol cm−2, respectively (Table 2). The results further demonstrate that the stronger light-harvesting capacity of RC sensitizers promotes the better JSC and PCE values compared to that of Z907. Considering the possibly serious electron recombination process by the large-sized electron-donating moieties of RC dyes compared to the long alkyl chain of the benchmark dye Z907, all RC dyes showed poorer VOC than Z907. To illustrate this, the electrochemical impedance spectroscopy (EIS)32 and dark current measurements were carried out.

13



45

Rs

40

Rpt

Rct

Cµ

Cµ

RC-41 RC-42 RC-43 Z907

35

-Z'' (Ω )

2

30

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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25 20 15 10 5 0 0

10

20

30

40

50

60

70

Z' (Ω) Figure 4. EIS plots of RC dyes and Z907 sensitized devices measured under dark. Experimental data are represented by dots and solid lines correspond to fitted data. The inset shows the electrical elements of the equivalent circuit in the DSSC.

As shown in Figure 4, the electrochemical impedance spectroscopy (EIS) of RC dyes and Z907-based DSSCs are measured at -0.70 V forward bias in the dark. The EIS spectra of DSSCs based on these dyes show two main semicircles. These two semicircles can be recognized and fitted according to an equivalent circuit. The fitting data results are given in Table 3. Apart from the total series resistance (Rs), the semicircle in the high frequency region represents interface impedance corresponding to charge transfer at the Pt/FTO counter electrode (Rpt/Cµ1), while the one in the low-frequency

region

dyed-TiO2/electrolyte

gives

the

interface

information (Rct/Cµ2)

on

the

related

impedance to

the

at

the

charge

transport/recombination.28 Considering that the fluctuation in charge transfer resistance (Rct) and chemical capacitance (Cµ) can also induce a difference in VOC, the variation of Rct and Cµ2 at different bias potentials is also presented (SI, Figure S1). 14


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The trend in the Rct and Cµ2 lie in the order of Z907 > RC-42 > RC-43 > RC-41, which is exactly consistent with the sequence of VOC. Besides, the electron lifetimes (τn(EIS)), according to the equation τn(EIS) = Rct × Cµ2, were calculated to be 40.8, 48.9, 47.3, and 126.6 ms for RC-41, RC-42, RC-43, and Z907, respectively. The higher

τn(EIS) indicate poor recombination occurring at the dyed-TiO2/electrolyte interface, hence resulting in a higher VOC in genenal.28 Due to the more significantly electron recombination occurred in the dyes with more bulky structure, the inferior VOC values of RC sensitizers are actually correlated with the large dimension electron-donating moieties compared to the alkyl chain in Z907.22 The curves of dark current measurements were displayed in Figure S2.32 Consisting with the results of EIS, the fact that dark current values of all the RC dyes were more negative than the cells based on the dye Z907 implies the higher rate of charge recombination in the RC dyes-based cells.

Table 3. Fitting results of EIS parameters for the DSSCs devices based on the RC dyes and Z907. Sensitizer

Rs [Ω]

Rpt [Ω]

Rct [Ω]

Cµ2 [mF]

τn(EIS) [ms]

RC-41

2.70

7.0

23.1

1.768

40.8

RC-42

2.76

5.6

29.6

1.651

48.9

RC-43

2.77

7.3

28.9

1.635

47.3

Z907

2.72

4.2

53.3

2.375

126.6

15



Based on the discussion above, the efficient interface modification which could fix the defects and improve the performance of RC dyes should be carried out urgently. A typical coadsorbent 1-decylphosphonic acid (DPA)16,22 was added to the dye staining solution. In the presence of DPA as a coadsorbent, better JSC and VOC were obtained obviously (Figure 5 and Table 4). The RC-43 sensitized device, in particular, provided the highest photocurrent (20.21 mA cm-2), appropriate photovoltage (0.731 V), and the best PCE of 10.78%. The solar cells sensitized by RC-41 and RC-42 also showed satisfactory photovoltaic parameters (JSC of 19.04 mA cm-2, VOC of 0.725 V, FF of 0.73, and η of 10.07% for RC-41; JSC of 19.83 mA cm-2, VOC of 0.737 V, FF of 0.72, and η of 10.52% for RC-42). The improved JSC and VOC were caused by the avoided aggregation of these RC dyes with DPA which could decrease the recombination and intermolecular charge transfer. These subsequent improvements reveal the great potential of these dyes with strong electron-donating antennas for DSSC application in the future.30,33-35 -2

Current Density (mA cm )

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Page 16 of 30

20 16

RC-41+DPA RC-42+DPA RC-43+DPA Z907 +DPA

12 8 4 0 0

200

400

600

800

Voltage (mV) Figure 5. J-V characterization for DSSC devices under AM 1.5G full-sunlight intensity. 16


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Table 4. Photovoltaic Parameters of DSSC Devices with the RC and Z907 Sensitizers in the Presence of DPA as Co-adsorbent under Full Sunlight Intensity. JSC Sensitizer

VOC

η FF

[mA cm-2]

[mV]

RC-41

19.04

0.725

0.73

10.07

RC-42

19.83

0.737

0.72

10.52

RC-43

20.21

0.731

0.73

10.78

Z907

17.39

0.752

0.74

9.67

[%]

To further elaborate the charge-separation and dyes’ regeneration, transient absorption spectra (TAS) were measured to observe the interfacial recombination and regeneration kinetics of the excited-state dye molecules with injected electrons in the conduction band of TiO2 or oxidized redox couple in the electrolyte (EL).36 As shown in Figure 6a, a negative peak is found in the region between 400 and 650 nm, which can be assigned to the bleaching of ground-state sensitizer molecules (S).37 The positive peak from 650 to 900 nm can be assigned to an electronic excitation of the dye cation (S+). Therefore, an excited wavelength of 500 nm and a probe wavelength of 750 nm were selected to investigate the decay of S+.

17



1.2

0.008

a

1.0

Normalized ∆ OD

Absorbance Change (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 30

0.000

-0.008

-0.016

RC-43+ACN RC-43+EL

b

0.8 0.6 0.4 0.2

-0.024

0.0

400

500

600

700

800

1E-6

900

Wavelength (nm)

1E-5

1E-4

1E-3

Time (s)

Figure 6. (a) The transient absorption change of dyed TiO2 film in ACN (The recorded time of transient spectrum is 500 ns). (b) The transient absorbance decay kinetics of the RC-43 dye cation (S+) adsorbed on TiO2 films in ACN and the EL with redox species.

In an inert solvent acetonitrile (ACN), the decay of the absorption signal indicates the recombination of TiO2 conduction band electrons with the S+. In the presence of the redox couple (in EL), the absorption decay shows the kinetics of the process that S+ could be regenerated by TiO2 conduction band electrons or by the oxidized redox couple in the EL.38 The transient absorbance decay kinetics of the dye cation of RC-43 adsorbed on TiO2 films in ACN and EL with redox species are shown in Figure 6b. The corresponding illustrations for RC-41 and RC-42 are given in Figure S3. According to the equation OD (∆t) = A0 + A1 e-∆t/τ, in the inert solution ACN, the fitted lifetime (τ) is 11.5 µs, 17.8 µs, and 14.4 µs for RC-41, RC-42, and RC-43, respectively. The absorbance decay was accelerated apparently when ACN was replaced with EL. The corresponding fitted lifetime (τ) are 2.5 µs, 1.4 µs, and 1.8 µs for RC-41, RC-42, and RC-43, respectively. The observation indicates the fact that 18


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the S+ can be regenerated favorably by both redox couple in the EL and the injected electrons in the TiO2 conduction band. These fitted lifetimes suggest the efficient charge separation and dye regeneration between the TiO2/dye/redox electrolyte interfaces. These results, in another aspect, make an explanation for the high JSC of the RC dyes. Long-term stability is very critical to evaluate the new RC dyes for further application. Low-volatility electrolyte (see the Experimental section) based DSSCs devices were used to assess the stability of the new sensitizers under visible light soaking at 60 °C. The photovoltaic performance during the test was recorded in detail. The devices based on all the RC sensitizers behaved similarly during the stability testing.

The

representative

variations

in

the

photovoltaic

parameters

of

RC-43-sensitized solar cells are displayed in Figure 7. The initial photovoltaic parameters (VOC, JSC, FF and PCE) are 0.68 V, 18.2 mA cm-2, 0.72 and 8.81%, respectively. During the test period, all the photovoltaic parameters of the cell changed slightly from the initial values. After the aging process, the value of the efficiency remained 93% of the initial value after 1000 h light soaking. The stable performance demonstrated that the RC sensitizer on TiO2 surface remained robust after long time light soaking.

19


Page 20 of 30

0.7 0.6

JSC (mA cm

-2

)

0.5 20 18 16

FF

0.8 0.6 0.4 PCE (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

VOC (V)


10 8 6

0

200

400

600

800

1000

Time (h)

Figure 7. Stability test photovoltaic parameter variations with aging time for the DSSCs based on RC-43-sensitized TiO2 film with low-volatility electrolyte under visible-light soaking.

3. CONCLUSIONS In summary, we designed and synthesized three new heteroleptic ruthenium sensitizers, RC-41, RC-42, and RC-43, by incorporating electron donating antennas into the ancillary ligands. These new sensitizers exhibited superior light-harvesting capacity. The DSSCs based on RC dyes obtained impressive power conversion efficiency closed to 11% under AM 1.5G one sun (100 mW cm-2). The devices employing RC dyes and a low-volatility electrolyte showed excellent performance and stability under long-term light soaking at 60 °C. These findings provide an alternative route to improving the light-harvesting capability of ruthenium sensitizer as well as the DSSCs performance.

20


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4. EXPERIMENTAL SECTION Materials and General Measurements. The

initiative

reagents

dichloro(p-cymene)

4,4'-dicarboxy-2,2'-bipyridine

were

ruthenium

purchased

(II)

from

dimer

and

Sigma-Aldrich.

4,4'-dibromo-2,2'-bipyridine and (9-phenyl-9H-carbazol-3-yl)boronic acid were purchased

from

TCI

and

employed

as

received.

N,N-bis(4-methoxyphenyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-aniline and N,N-bis(4-methoxyphenyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thieno[3,4 -b]-1,4-dioxin-2-yl)-aniline were prepared according to the literature procedures22. The solvents and other materials used were puriss grade and applied without further refining. 1

H NMR spectra were carried out on Bruker Advance 400 spectrometer. Mass

spectra (MS) were measured with LTQ Orbitrap XL Mass Spectrometer. The UV-Vis spectra of these sensitizers and the dye loaded TiO2 films were obtained by Hitachi spectrophotometer U-3900H. Cyclic voltammetry (CV) were measured on CHI-660d electrochemical analyzer in a typical three-electrode electrochemical cell. A glassy carbon (GC) electrode, a platinum wire, and an SCE were used as working electrode, counter electrode, and reference electrode, respectively. The supporting electrolyte was 0.1 M tetrabutylammonium perchlorate (TBAP) in dimethylformamide (DMF) solution. The scan rate was 50 mV s-1. The morphology of the TiO2 sub-microspheres samples was observed by scanning electron microscopy (FEI XL-30 SFEG coupled to 21



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a TLD) and transmission electron microscopy (JEM-200CX, JEOL).

Photovoltaic Characterization. The incident monochromatic photon-to-current conversion efficiency (IPCE) spectra were recorded on Newport QE/IPCE measurement kit. The photocurrent density-voltage (J-V) characteristics of the solar cells were measured by Newport 3A grade solar simulator. The electrochemical impedance spectroscopy (EIS) was studied using Autolab PGSTAT 302N analyzer (Metrohm, Switzerland) in the frequency region from 50 mHz to 1000 kHz. In conjunction with a nanosecond tunable laser (OPOLette 355II. Opotek, Inc., CA), transient absorption spectra were investigated by laser flash spectrophotometer (LP920, Edinburgh Instruments Ltd. Scotland).

Assembly of Dye-Sensitized Solar Cells (DSSCs). The photoanode films were screen-printed on the fluorine doped SnO2 conducting glass (12−14 Ω per square, TEC 15, USA) through a 34T meshsize screen according to our previous paper.27,

28

Primarily, a 20 nm sized TiO2 particles film with a

thickness of 4 µm was printed on FTO and then coated by 16 µm thick layers of TiO2 sub-microspheres. Then, the TiO2 films were sintered at 450 °C for 30 min in air. After cooling down, the TiO2 thin film electrodes were immersed in an tert-butanol/acetonitrile/DMF (45:45:10, v/v/v) mixed solvent containing 300 µM dye sensitizers (with or without 150 µM 1-decylphosphonic acid, DPA) for 16 h, then cleaned with anhydrous acetonitrile (MeCN) and dried by air flow. By spreading out a 22


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drop of 5 mM H2PtCl6 solution on FTO glass, the counter electrode was prepared and sintered at 450 °C for 25 min. The two electrodes were separated by a thermal adhesive film and sealed by heating. The electrolyte solution was a mixture of 1 M 1,3-dimethyl-imidazolium iodide (DMII), 100 mM LiI, 60 mM I2, 0.5 M TBP and 0.1 M Guanidinium thiocyanate (GuNCS) in a solvent mixture of 85% acetonitrile with 15% valeronitrile by volume. A low volatility electrolyte was applied for long-term stability testing, containing 1 M DMII, 0.15 M I2, 0.5 M N-butylbenzimidazole, and 0.1 M GuNCS in methoxypropionitrile. Prior to measurements the sensitized cells were masked by a square black tape with a 5 × 5 mm2 aperture.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Detailed synthetic route, characterization of synthesized ligands and sensitizers, dark current measurement, and additional EIS and TAS results.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. Phone: +86 55165593222. *E-mail: [email protected]. Phone: +86 1061772407. *E-mail: [email protected]. Phone: +86 1061772268. 23



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Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National High Technology Research and Development Program of China (No.2015AA050602) and Natural Science Foundation of Anhui Province (No.1508085SMF224).

REFERENCES (1) Robertson, N., Catching the Rainbow: Light Harvesting in Dye-Sensitized Solar Cells. Angew. Chem. Int. Ed. 2008, 47, 1012-1014. (2) O’regan, B.; Grätzel, M., A Low-Cost, High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films. Nature 1991, 353, 737-740. (3) Tang, Y.; Wang, Y.; Li, X.; Ågren, H.; Zhu, W.-H.; Xie, Y., Porphyrins Containing a Triphenylamine Donor and up to Eight Alkoxy Chains for Dye-Sensitized Solar Cells: A High Efficiency of 10.9 %. ACS Appl. Mater. Interfaces 2015, 7, 27976-27985. (4) Lu, J.; Li, H.; Liu, S.; Chang, Y.; Wu, H.; Cheng, Y.; Wei-Guang Diau, E.; Wang, M., Novel Porphyrin-Preparation, Characterization, and Applications in Solar Energy Conversion. Phys. Chem. Chem. Phys. 2016, 18, 6885-6892. (5) Mao, M.; Song, Q., The Structure-Property Relationships of D-π-A BODIPY Dyes for Dye-sensitized Solar Cells. Chem. Rec. 2016, 16, 719-733. (6) Srinivasan, V.; Panneer, M.; Jaccob, M.; Pavithra, N.; Anandan, S.; Kathiravan, A., A 24


Page 24 of 30

Page 25 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Diminutive Modification in Arylamine Electron Donors: Synthesis, Photophysics and Solvatochromic Analysis - towards the Understanding of Dye Sensitized Solar Cell Performances. Phys. Chem. Chem. Phys. 2015, 17, 28647-28657. (7) Wu, K. L.; Li, C. H.; Chi, Y.; Clifford, J. N.; Cabau, L.; Palomares, E.; Cheng, Y. M.; Pan, H. A.; Chou, P. T., Dye Molecular Structure Device Open-Circuit Voltage Correlation in Ru(II) Sensitizers with Heteroleptic Tridentate Chelates for Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2012, 134, 7488-7496. (8) Ardo, S.; Meyer, G. J., Photodriven Heterogeneous Charge Transfer with Transition-metal Compounds Anchored to TiO2 Semiconductor Surfaces. Chem. Soc. Rev. 2009, 38, 115-164. (9) Argazzi, R.; Bignozzi, C. A.; Heimer, T. A.; Castellano, F. N.; Meyer, G. J., Long-Lived Photoinduced Charge Separation across Nanocrystalline TiO2 Interfaces. J. Am. Chem. Soc. 1995, 117, 11815-11816. (10) Ozawa, H.; Sugiura, T.; Kuroda, T.; Nozawa, K.; Arakawa, H., Highly Efficient Dye-Sensitized Solar Cell Based on a Ruthenium Sensitizer Bearing a Hexylthiophene Modified Terpyridine Ligand. J. Mater. Chem. A 2016, 4, 1762-1770. (11) Chou, C. C.; Chen, P. H.; Hu, F. C.; Chi, Y.; Ho, S. T.; Kai, J. J.; Liu, S. H.; Chou, P. T., Structural Tuning of Ancillary Chelate in Tri-Carboxyterpyridine Ru(II) Sensitizers for Dye Sensitized Solar Cells. J. Mater. Chem. A 2014, 2, 5418-5426. (12) Yu, Q.; Wang, Y.; Yi, Z.; Zu, N.; Zhang, J.; Zhang, M.; Wang, P., High-Efficiency Dye-Sensitized Solar Cells: The Influence of Lithium Ions on Exciton Dissociation, Charge Recombination, and Surface States. ACS Nano 2010, 4, 6032-6038. (13) Han, W. S.; Han, J. K.; Kim, H. Y.; Choi, M. J.; Kang, Y. S.; Pac, C.; Kang, S. O., Electronic 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Optimization of Heteroleptic Ru(II) Bipyridine Complexes by Remote Substituents: Synthesis, Characterization, and Application to Dye-Sensitized Solar Cells. Inorg. Chem. 2011, 50, 3271-3280. (14) El-Shafei, A.; Hussain, M.; Islam, A.; Han, L., Structure-Property Relationship of Hetero-Aromatic-Electron-Donor Antennas of Polypyridyl Ru (II) Complexes for High Efficiency Dye-Sensitized Solar Cells. Prog. Photovoltaics 2014, 22, 958-969. (15) Huang, J. F.; Liu, J. M.; Su, P. Y.; Chen, Y. F.; Shen, Y.; Xiao, L. M.; Kuang, D. B.; Su, C. Y., Highly Efficient and Stable Cyclometalated Ruthenium(II) Complexes as Sensitizers for Dye-Sensitized Solar Cells. Electrochim. Acta 2015, 174, 494-501. (16) Wang, P.; Zakeeruddin, S. M.; Humphry-Baker, R.; Moser, J. E.; Grätzel, M., Molecular-Scale Interface Engineering of TiO2 Nanocrystals: Improve the Efficiency and Stability of Dye-Sensitized Solar Cells. Adv. Mater. 2003, 15, 2101-2104. (17) Cao, Y. M.; Bai, Y.; Yu, Q. J.; Cheng, Y. M.; Liu, S.; Shi, D.; Gao, F. F.; Wang, P., Dye-Sensitized Solar Cells with a High Absorptivity Ruthenium Sensitizer Featuring a 2-(Hexylthio)thiophene Conjugated Bipyridine. J. Phys. Chem. C 2009, 113, 6290-6297. (18) Chen, C. Y.; Wang, M. K.; Li, J. Y.; Pootrakulchote, N.; Alibabaei, L.; Ngoc-le, C. H.; Decoppet, J. D.; Tsai, J. H.; Gratzel, C.; Wu, C. G.; Zakeeruddin, S. M.; Grätzel, M., Highly Efficient Light-Harvesting Ruthenium Sensitizer for Thin-Film Dye-Sensitized Solar Cells. ACS Nano 2009, 3, 3103-3109. (19) M. Grätzel, Presented at DSC-IC3, 2009, Nara, Japan. (20) Chen, C. Y.; Chen, J. G.; Wu, S. J.; Li, J. Y.; Wu, C. G.; Ho, K. C., Multifunctionalized Ruthenium-Based Supersensitizers for Highly Efficient Dye-Sensitized Solar Cells. Angew. Chem. 26


Page 26 of 30

Page 27 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Int. Ed. 2008, 47, 7342-7345. (21) She, Z.; Cheng, Y.; Zhang, L.; Li, X.; Wu, D.; Guo, Q.; Lan, J.; Wang, R.; You, J., Novel Ruthenium Sensitizers with a Phenothiazine Conjugated Bipyridyl Ligand for High-Efficiency Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 27831-27837. (22) Cao, K.; Lu, J.; Cui, J.; Shen, Y.; Chen, W.; Alemu, G.; Wang, Z.; Yuan, H.; Xu, J.; Wang, M., Chen, Y., Highly Efficient Light Harvesting Ruthenium Sensitizers for Dye-Sensitized Solar Cells Featuring Triphenylamine Donor Antennas. J. Mater. Chem. A 2014, 2, 4945-4953. (23) Jin, Z. Z.; Masuda, H.; Yamanaka, N.; Minami, M.; Nakamura, T.; Nishikitani, Y., Triarylamine-Functionalized Ruthenium Dyes for Efficient Dye-Sensitized Solar Cells. ChemSusChem 2008, 1, 901-904. (24) Chen, C. Y.; Pootrakulchote, N.; Wu, S. J.; Wang, M. K.; Li, J. Y.; Tsai, J. H.; Wu, C. G.; Zakeeruddin, S. M.; Gratzel, M., New Ruthenium Sensitizer with Carbazole Antennas for Efficient and Stable Thin-Film Dye-Sensitized Solar Cells. J. Phys. Chem. C 2009, 113, 20752-20757. (25) Chen, C. Y.; Wu, S. J.; Li, J. Y.; Wu, C. G.; Chen, J. G.; Ho, K. C., A New Route to Enhance the Light-Harvesting Capability of Ruthenium Complexes for Dye-Sensitized Solar Cells. Adv. Mater. 2007, 19, 3888-3891. (26) Lou, X. W. D.; Archer, L. A.; Yang, Z., Hollow Micro-/Nanostructures: Synthesis and Applications. Adv. Mater. 2008, 20, 3987-4019. (27) Li, Z.-Q.; Ding, Y.; Mo, L.-E.; Hu, L.-H.; Wu, J.-H.; Dai, S.-Y., Fine Tuning of Nanocrystal and Pore Sizes of TiO2 Submicrospheres toward High Performance Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 22277-22283. 27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(28) Ding, Y.; Zhou, L.; Mo, L. e.; Jiang, L.; Hu, L.; Li, Z.; Chen, S.; Dai, S., TiO2 Microspheres with Controllable Surface Area and Porosity for Enhanced Light Harvesting and Electrolyte Diffusion in Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2015, 25, 5946-5953. (29) Chen, Y.; Huang, F.; Chen, D.; Cao, L.; Zhang, X. L.; Caruso, R. A.; Cheng, Y. B., Effect of Mesoporous TiO2 Bead Diameter in Working Electrodes on the Efficiency of Dye-Sensitized Solar Cells. ChemSusChem 2011, 4, 1498-1503. (30) Chen, W.; Kong, F.; Liu, X.; Guo, F.; Zhou, L.; Ding, Y.; Li, Z.; Dai, S., Effect of Electron-Donor Ancillary Ligands on The Heteroleptic Ruthenium Complexes: Synthesis, Characterization, and Application to High Performance Dye-Sensitized Solar Cells. Phys. Chem. Chem. Phys. 2016, 18, 11213-11219. (31) Vougioukalakis, G. C.; Philippopoulos, A. I.; Stergiopoulos, T.; Falaras, P., Contributions to the Development of Ruthenium-Based Sensitizers for Dye-Sensitized Solar Cells. Coord. Chem. Rev. 2011, 255, 2602-2621. (32) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H., Dye-Sensitized Solar Cells. Chem. Rev. 2010, 110, 6595-6663. (33) Mishra, A.; Pootrakulchote, N.; Wang, M. K.; Moon, S. J.; Zakeeruddin, S. M.; Gratzel, M.; Bauerle, P., A Thiophene-Based Anchoring Ligand and Its Heteroleptic Ru(II)-Complex for Efficient Thin-Film Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2011, 21, 963-970. (34) Shi, Y. B.; Liang, M.; Wang, L. N.; Han, H. Y.; You, L. S.; Sun, Z.; Xue, S., New Ruthenium Sensitizers Featuring Bulky Ancillary Ligands Combined with a Dual Functioned Coadsorbent for High Efficiency Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2013, 5, 144-153. (35) Han, L.; Islam, A.; Chen, H.; Malapaka, C.; Chiranjeevi, B.; Zhang, S.; Yang, X.; Yanagida, 28


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M., High-Efficiency Dye-Sensitized Solar Cell with a Novel Co-Adsorbent. Energy Environ. Sci. 2012, 5, 6057-6060. (36) Daeneke, T.; Mozer, A. J.; Uemura, Y.; Makuta, S.; Fekete, M.; Tachibana, Y.; Koumura, N.; Bach, U.; Spiccia, L., Dye Regeneration Kinetics in Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2012, 134, 16925-16928. (37) Sabatini, R. P.; Eckenhoff, W. T.; Orchard, A.; Liwosz, K. R.; Detty, M. R.; Watson, D. F.; McCamant, D. W.; Eisenberg, R., From Seconds to Femtoseconds: Solar Hydrogen Production and Transient Absorption of Chalcogenorhodamine Dyes. J. Am. Chem. Soc. 2014, 136, 7740-7750. (38) Hsu, H.-Y.; Cheng, C.-W.; Huang, W.-K.; Lee, Y.-P.; Diau, E. W.-G., Femtosecond Infrared Transient Absorption Dynamics of Benzimidazole-Based Ruthenium Complexes on TiO2 Films for Dye-Sensitized Solar Cells. J. Phys. Chem. C 2014, 118, 16904-16911.

29



Table of contents

Electron donating antenna N N NC S N Ru N NC S

HOOC

20

HOOC

16

-2

J (mA cm )

e-

ee-

e-

N N NC S N Ru N NC S

HOOC

HOOC

e-

TiO2

12

RC-42 η = 10.52%

4

RC-43 η = 10.84%

0 0 N N

N C S

600

800

N N C S

N

OCH3

OCH3 H3CO

H3CO

HOOC HOOC

400

N

Ru

HOOC

200

Voltage (mV)

HOOC

e-

RC-41 η = 10.16%

8

N

N

N

N N N CN N S C S Ru

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 30

O O

30


S

Superior Light-Harvesting Heteroleptic Ruthenium(II

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