Synthesis and Characterization of Novel Î²-Bis(N,N-diarylamino

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Synthesis and Characterization of Novel #-Bis(N,Ndiarylamino) Substituted Porphyrin for Dye-Sensitized Solar Cells under One Sun and Dim Light Conditions Kamani Sudhir K Reddy, Yu-Chieh Liu, Hsien-Hsin Chou, Kannankutty Kala, Tzu-Chien Wei, and Chen-Yu Yeh ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14457 • Publication Date (Web): 31 Oct 2018 Downloaded from http://pubs.acs.org on October 31, 2018

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ACS Applied Materials & Interfaces

Synthesis and Characterization of Novel β-Bis(N,N-diarylamino) Substituted Porphyrin for Dye-Sensitized Solar Cells under One Sun and Dim Light Conditions Kamani Sudhir K. Reddy,a Yu-Chieh Liu,b Hsien-Hsin Chou,a Kannankutty Kalab, Tzu-Chien Wei,*b and Chen-Yu Yeh*a,c aDepartment bDepartment cResearch

of Chemistry, National Chung Hsing University, Taichung 402, Taiwan

of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan

Center for Sustainable Energy and Nanotechnology (RCSEN) and Innovation and

Development Center of Sustainable Agriculture (IDCSA), National Chung Hsing University, Taichung 402, Taiwan E-mail: [email protected], [email protected] Abstract In this work, we have synthesized a novel porphyrin dye named SK7, which contains two N,N-diarylamino moieties at two beta-positions as electron-donating units and one carboxy phenylethynyl moiety at meso-position as an electron-withdrawing, anchoring group. This novel dye was tested for the application in dye-sensitized solar cells (DSSCs). The light-harvesting behavior for SK7 and YD2 have been investigated by using UV-vis absorption and density functional calculation. The electron transport properties at TiO2/dye/electrolyte interface for SK7 and YD2-based devices were evaluated by the electrochemical impedance spectroscopy. X-ray crystallographic characterization is conducted to understand the influence of two N,N-diarylamino units at two beta-positions. The PCEs ca. 6.54% under one sun illumination (AM1.5G), and ca. 19.72% under T5 light source, were noted for SK7 dye. The performance of SK7 is comparable to dye YD2 which contains only one N,N-diarylamino moiety at meso-position (ca. 7.78% and ca. 20.00% under one sun and T5 light, respectively). Keywords: β-substituted porphyrin, dye-sensitized solar cells, dim light, X-ray crystallography, density functional theory.

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1

Introduction Presently, crystalline silicon solar cells (c-SiSCs) are holding major share in the

commercial market of solar cells, although they have several disadvantages.1 For instance, the high-cost to manufacture big module, long energy recovery time, tedious synthetic procedure to manufacture crystalline silicon (c-Si)2 and poor cell performances under indoor light conditions. Recently, a new solar cell technology called perovskite solar cells (PSCs) is introduced, started with PCE of ca. 3.8% in 20093 now they are at 21.2%,4 its growth in such a short span of time is unprecedented.5 Though they are excellent light-to-electricity converting devices, they are also acknowledged to have noticeable drawbacks such as instability and toxicity.6 Because of their ease of fabrication, low-cost of manufacture,7-9 and the possibility to utilize colorful,10 flexible11 modules as decorative power converting windows,12-15 dye-sensitized solar cells (DSSCs) are undoubtedly the ideal candidates to compete with either c-SiSCs or PSCs, when it comes to mainstream commercial applications.16 A large number of dyes were reported with excellent performances under one sun (AM 1.5G) illumination,17 like ruthenium complexes,18-19 zinc porphyrins,17,

20-23

and metal-free organic dyes.24 Interestingly, the dyes categorized as zinc

porphyrins are holding benchmark efficiencies22 and high stability of these devices is an added advantage.14,

25-30

A few of such porphyrin-based sensitizers with >10% power conversion

efficiencies (PCEs) are YD2,31 YD2-o-C8,32 GY50,33 LD14,34 XW9- XW11,35 XW15-XW17,35 ZnPBAT,36 SM371 and SM315.37 Zinc porphyrin-based sensitizers with donor and acceptor entities (push-pull) are well documented,22-23, 30 because of their excellent capability of capturing and converting incident lightto-electricity. They are also very interesting chromophores for researchers as the availability of four meso- and eight beta-positions for any synthetic modifications, most importantly, the incorporation of donor or acceptor entities at meso-position is easy to access with high yields via palladium catalyzed cross coupling reactions.38 For instance, aforementioned dyes such as YDseries, LD-series, XW-series, and SM-series were based on the attachment of donor or acceptor moieties at meso-positions. However, the exploration of dyes with donor moiety at meso-position is outdated, due to no further enhancement in PCE based on this strategy. On the other hand, betafunctionalized dyes with moderate cell performances were started reporting few years ago.39-43 Dong-Ho Kim and co-workers reported vinylene- and diene-bridged acceptors at beta-position 2 ACS Paragon Plus Environment

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with PCE of 3.60% (5.30%) and 7.50% (8.20%) by using iodide/triiodide (Cobalt(II/III)) redox couple, respectively.44-46 The idea of incorporating acceptor entities at beta-carbons has been employed by the aforementioned studies, but incorporating one or two donor moieties at betacarbons is yet to be explored. A close look into the benchmark dyes such as YD-series, GY-series, and SM-series reveal that a N,N-diarylamino donor entity at meso-position is the most common electron-donating group, and this donor plays a significant role in charge separation, which in turn gives enhanced VOC values. Owing to its rich electron donating ability, flexibility, excellent charge separation character, and possibility to introduce additional long alkyl/alkoxy chains at para- or meta-positions of N-phenyl rings; this donor entity has got a great deal of interest. Although its substitution at meso-position is highly successful, no exploration of such a donor at beta-position for DSSC application is reported until now.47 A monoarylamino substitution at beta-position is recently reported,48 but only a PCE of ca. 1.45% was noted. To overcome this gap, we have designed a novel dye with two N,N-bis(4-hexylphenyl)amine moieties positioned at two symmetrical beta-carbons of zinc porphyrin and named it as SK7 (Figure 1). The Soret band of this dye is expected to split as two strong electron donating groups were placed at two betapositions,49 which would fill up the dip between the Soret and Q bands. In addition, this dye would sufficiently block the contact of redox mediator toward the TiO2, as it has four hexyl chains on the donor moieties. This novel dye SK7 was tested for photovoltaic properties under one sun illumination, and the results were compared with those of benchmark dye YD2. The chemical structures of SK7 and YD2 were shown in Figure 1. Twenty first century has welcomed a paradigm shift in consumer-based microelectronic devices and considered as the golden period for such electronic devices, best example of its kind is Internet of Things (IoTs).50-51 The tiny amount of electricity (10 – 100 µW) required for their continuous run,52 can be supplied through DSSCs.13, 53 Because of this reason, we have also tested the photovoltaic properties of SK7 and YD2 under dim light environments. A PCE of ca. 19.72% and ca. 15.42% for SK7, and a PCE of ca. 20.00% and ca. 16.47% for YD2, were achieved under T5 fluorescent tube and commercial LED lamp, respectively. The large Pout values under these indoor light sources indicate that the device based on SK7 is competitive when compared with that of YD2.



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R R R

R R

N

R

N N

N

N

N

N

N

Zn N

SK7

Zn

N N

R=

C6H13

YD2 COOH

COOH

Figure 1. Chemical structures of SK7 and YD2. 2 2.1

Results and discussion Synthesis of SK7 As shown in Scheme 1, Grignard reagent mediated acylation of bis(1H-pyrrol-2-

yl)methane (2) with 3,5-di-tert-butylbenzoylchloride (1) gave 5,5'-methylenebis(1H-pyrrole-5,2diyl))bis((3,5-di-tert-butylphenyl)methanone (3) with 54% yield.54-56 The compound 3 was then brominated by using bromine, to get 5,5'-methylenebis(4-bromo-1H-pyrrole-5,2-diyl))bis((3,5-ditert-butylphenyl)methanone (4) with 46% yield.55 The brominated di-ketone 4 was first reduced to corresponding diol (5) by using excess equivalents of NaBH4 in THF:MeOH (3:1, v/v), followed by isolating the corresponding diol (5) as a crude product.55 This diol (5) was combined with 2,2'-(3-(triisopropylsilyl)prop-2-yne-1,1-diyl)bis(1H-pyrrole) (6) in dry CH3CN, and condensed by using trifluoroacetic acid, then oxidized with DDQ to get β-bis-brominated porphyrin (7), which was purified by using short-plug silica gel flash column chromatography.55 The free base porphyrin (7) was then metallated by using Zn(OAc)2·2H2O to get compound 8. A Buchwald-Hartwig amination of compound 8 with N,N-bis(4-hexylphenyl)amine (9) was carried out to get compound 10 with 33% - 41% yield,31-32, 57 the crystal structure of compound 10 was given in Figure 2. The silyl protection on terminal acetylene group of compound 10 was removed by using 1M TBAF ([CH3(CH2)3]4NF) as fluoride ion source, then a Sonogashira cross coupling reaction32, 58 was performed on this de-protected compound 10 with 4-iodobenzoic acid to get the desired novel dye SK7 in 62% yield. We have tried to grow the crystal for SK7 dye, however, it was unsuccessful as the solubility of SK7 is high. This dye SK7 was synthesized under four steps post condensation/oxidation, and the only limitation of this synthetic procedure is low yield (19%) 4 ACS Paragon Plus Environment

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for condensation/oxidation. Synthetic procedure for YD2 can be seen elsewhere,31, 49, 59-60 and the synthetic procedures for compound 1, and compound 6, were given in Scheme S1, and Scheme S2 , respectively, in Supporting Information. (i), (ii) N H

N H

O N H

2

3

N O H

(iii)

COCl

BrBr

1

O N H

N O H

4

(iv) 6 N H C6H13

R=

N H

+

BrBr HO N H

Si

N

(v) (7), (vi)

C6H13

R

R

N N Zn N N

R (viii)

SK7

5 N OH H

R

Br

Br (vii)

N N Zn N N

H N

N N Zn N N

10

+ C6H13 8

Si

Si

C6H13 9

HO O

Scheme 1. Synthesis of SK7. (i) 1 M EtMgBr, THF (ii) 1, THF, 54% (iii) Br2, CHCl3, 45.8%. (iv) NaBH4, THF : MeOH, 0 0C → rt (v) Trifluoroacetic Acid, DDQ, acetonitrile, rt, 19%. (vi) Zn(OAc)2, CH2Cl2:Methanol (1/0.5, v/v), 95%. (vii) 9, NaH (60%), Pd(OAc)2, DPEPhos, Toluene, 41%. (viii) TBAF, Pd2(dba)3, ASPh3, NEt3, THF, 62%. a The synthetic procedures of compound 1, and 6 are given in Supporting Information. 2.2

X-ray crystallographic details of intermediate compound 10 and comparison with DFT optimized geometries A single crystal was grown for the intermediate compound 10 by slowly diffusing methanol

into CH2Cl2 solution, to understand the influence of two beta-substituted N,N-diarylamino units on the 24 atom mean plane of the porphyrin cycle. The solved crystal structure (one methanol molecule was chelated with zinc) was shown in Figure 2 (CCDC 1855658), in which zinc atom is placed at 0.280 Å above the mean plane, distance of Zn and N(1-4) is between 2.051 Å and 2.075 Å. The mean plane deviation of the solved single crystal of compound 10 was compared with the DFT optimized geometry, a formal diagram was given in Figure 3a, 3b. Strong intramolecular steric congestion between the hydrogens of C36, C40, C48, C52, C60, C64, C72, C76 (of N,N5 ACS Paragon Plus Environment


diarylamino moieties) and the hydrogens of C10 (meso), C7, C13 (beta), has slightly caused to deviate the plane of the porphyrin to some extent. However, the porphyrin containing the N,Ndiarylamino unit at meso-position instead of beta-position has caused negligible deformations to all atoms from 24 atom mean plane of the porphyrin ring (Figure S1). The possible dihedral angles (Ψ) between the N,N-diarylamino units at beta or meso-positions and the 24 atom mean plane of the porphyrin ring were shown in Figure S2 and Table S2. As can be seen, Ψ1, Ψ2 of betasubstituted one is lower than the Ψ1 of the meso-substituted one, which implies that the electronic communication between the beta-substituted donor moieties and porphyrin unit will obviously be superior to the electronic communication between the meso-substituted donor moiety and porphyrin unit.

Figure 2. ORTEP diagram of intermediate compound 10 (ellipsoids were drawn at 50% probability level, terminal alkyl chains of N,N-diarylamine, tert-butyl groups of meso-phenyl rings were omitted for clarity). The X-ray crystallographic details of compound 10 are deposited at CCDC 1855658.


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a)

b)

N5 +0.217

-0.562

+0.216 +0.089 +0.093

+0.257 +0.150 +0.100

+0.150 +0.092

-0.558

-0.172

+0.136

+0.073

+0.177

N2 +0.025 +0.032 +0.136

+0.015

+0.254

+0.290

+0.172

+0.190

+0.216 +0.077 +0.226

N3

+0.041

+0.102 +0.070

Zn +0.187

+0.009 -0.014 N

+0.125 +0.012 N1

+0.016 +0.181 N4 +0.035

+0.291 N6

-0.328

-0.220

Zn +0.280

1

-0.317

-0.194 +0.033

+0.042 +0.013 N

N5

-0.367

N3

N2

+0.092

-0.249

N6

4

+0.010 +0.083

0.120

-0.192

-0.259

Figure 3. Formal diagram indicating the deviations (Å) of the selected atoms from 24 atom mean plane of the porphyrin macrocycle, for single crystal structure (a) and DFT optimized structure (b) of compound 10. 2.3

Photophysical and electrochemical properties As shown in Figure 4, the UV-visible absorption spectrum of SK7 has four absorption

maxima (λmax), as expected, the Soret band of SK7 dye splits into two peaks with λmax at 424 nm (1.54 / ε =105 M-1 cm-1), and 491 nm (1.00). The replacement of hydrogen atom/atoms at beta or meso-positions with electron rich donor entities would alter the Gouterman Four Orbital model, as a result, one would expect perturbations to the degeneracy of a1u/a2u or eg orbitals. For instance, dyes YD14 and YD15 bearing two N,N-diarylamino moieties have shown split in their Soret band,60 similar observations were also witnessed in the case of ZnPBAT-type dyes.36, 61 Whereas, the dye YD2 had only three absorption maxima, a Soret-band at 444 nm (1.79) and two Q-bands at 589 nm (0.10) and 645 nm (0.27). As can be seen in Figure 4, the broad absorption spectrum (400 – 680 nm) of SK7 dye may benefit to enhance the light harvesting efficiency by capturing additional photons at this region, when compared with YD2 dye. Although SK7 is bearing two N,N-bis(4-hexylphenyl)amino moieties at two beta-positions, which is extending the πconjugation, we did not notice any redshift for Soret- or Q- bands, when compared with YD2. As seen in Figure S3 the absorption wavelengths of SK7 and YD2 are in close conjunction with the 7 ACS Paragon Plus Environment


emission wavelengths of incident light, i.e., either T5 or LED light. A detailed discussion about the origin of the split for Soret band of SK7 dye was given in theoretical investigation. The UVvisible absorption spectra of SK7 and YD2 loaded in TiO2 surface were given in Figure S5, in Supporting Information.

Figure 4. UV-visible absorption spectra of SK7 and YD2 performed at 25 oC using dry THF. Table 1. Photophysical and electrochemical properties of SK7 and YD2. E1/2ox / E1/2red b E0-0 c EHOMO ELUMO λmax (ε) a / 5 -1 -1 (V vs NHE) (V vs NHE) (V vs NHE) (V vs NHE) nm (10 M cm ) 424 (1.54) 491 (1.00) +0.88, +1.18d / SK7 1.91 0.88 -1.03 597 (0.25) 1.09 643 (0.14) 444 (1.79) +0.89, +1.29d / YD2 1.89 0.89 -1.01 589 (0.10) 1.09 645 (0.27) a Molar absorption coefficient values were calculated from UV-visible absorption spectra recorded in dry THF at 25 oC. b Oxidation and reduction potentials of SK7 were obtained from cyclic voltammetry experiments recorded at 25 oC in dry THF, 0.1 M TBAPF6 solution was used as the electrolyte. The potentials of YD2 were obtained from ref 50. c The optical band gaps were obtained from the formula E0-0 – 1240/λonset (Figure S4). d the potential was reported as Epa. Dye

To understand the electrochemical properties of SK7, we have performed cyclic voltammetry experiments at 25 oC by using THF as the solvent, which contains 0.1 M (nBu)4N]PF6 as an electrolyte. As shown in Figure 5a, SK7 has exhibited two oxidation potentials (Eox1 = +0.88 V and Epa = +1.18 V) and one reduction potential (Ered = -1.09 V). The first and second oxidation potentials of YD2 reported are at Eox1 = +0.89 V and Epa = +1.29 V, respectively, 8 ACS Paragon Plus Environment

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and reduction potential (Ered) is at -1.09 V.60 The comparison of electrochemical properties between SK7 and YD2 reveal that SK7 has a slight cathodic shift of 0.01 V for Eox1. The first reduction of both the dyes occur at the same potential. The schematic energy level diagrams of SK7 and YD2 were shown in Figure 5b, which reveal that the LUMO energy levels of both the dyes are located far negative than that of the Fermi level of TiO2 and the driving forces for charge injection (ΔGinj) from excited state (LUMO) of SK7 and YD2 are -0.53 eV and -0.51 eV, respectively. The HOMO energy levels of both the dyes are positive than iodide-based redox couple and the driving forces for charge regeneration (ΔGreg) of oxidized SK7 and YD2 are -0.48 eV and -0.49 eV, respectively. The calculated driving forces for charge injection and dye regeneration indicate that SK7 dye is feasible to the working model of DSSCs and nearly similar to that of YD2. The absorption and electrochemical data along with the HOMO and LUMO energy levels are listed in Table 1.

Figure 5. (a) Cyclic voltammogram of SK7 in THF containing 0.1 M (n-Bu)4N]PF6 at 25 oC, potentials were calibrated with respective to ferrocene/ferrocenium (0.63 V vs NHE). (b) Energy level diagrams of SK7 and YD2. 2.4

Theoretical investigation Table 2 displays frontier orbitals for YD2 and SK7 and model compound ZnP. A group of

the molecular orbitals HOMO-1, HOMO, LUMO and LUMO+1 for ZnP clearly represents the Gouterman Four Orbitals.62 For YD2, the HOMO (and HOMO-2) mainly populated at substituted electron-donating diarylamino group at porphyrin meso-5-position due to significant π contributions of ZnP HOMO on meso carbons. In the case of beta-bis-aminated SK7, while HOMO is also populated on porphyrin and the two diarylamino entities, it is originated from orbital 9 ACS Paragon Plus Environment


mixing of amines and  orbitals of ZnP core. On the other hand, SK7 and YD2 have quite resemble frontier unoccupied orbitals for functionalization of electron-withdrawing ethynylbenzoic acid occurs both at porphyrin meso-15-position. Compared to mono-substituted YD2, substitution of two diarylamino groups also result in slightly higher HOMO of SK7.

Figure 6. Experimental and TDDFT simulated UV-vis absorption spectra. The vertical excitation behavior for both porphyrin dyes were examined theoretically via TDDFT calculation at the same level (shown in Table 3). Figure 6 compares the UV-vis absorptions in THF and simulated spectra according to TDDFT results. The lowest-energy S0→S1 excitation is at 1.89 eV for YD2 and at 1.92 eV for SK7, which meets the experimental spectroscopic observations. For YD2, the Q-band is mainly composed of S0→S1 excitation (f = 0.30) containing prominent charge-transfer character, whereas much localized S0→S5 (f = 1.25) and S0→S6 (f = 0.67) excitations constitute of Soret band. This phenomenon also quite resembles our previous conclusion on meso-substituted derivatives.63 In the case of SK7, substitution occurs at both meso- and beta-positions, which will undoubtedly affect the corresponding electronic structure and vertical excitation behavior. As a result, splitting of Soret band leads to a new broad band at ca. 450 - 550 nm for SK7. This is mainly composed of S0→S3 (f = 0.29) and S0→S6 (f = 0.62) excitations where a large component of localized π-π* transitions participate in addition to charge-transfer transitions, as shown in Table 3 and Figure 6. Slightly blue shifted Soret band also occurs for SK7 and is mainly composed of S0→S8 and S0→S9 transitions (f = 1.22 and 0.71, respectively). Note that for Q-band of the porphyrin dyes, the major (S0→S3) transition for SK7 is 10 ACS Paragon Plus Environment

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higher in energy and possesses more localized character, i.e., HOMO‒x→LUMO+1, compared to relative non-localized S0→S1 transition (HOMO→LUMO) for YD2. This is probably indicative of drawback for SK7 considering the electron injection. Table 2. The Frontier molecular orbital diagrams of dyes ZnP, YD2, and SK7.a ZnP

YD2

LUMO +3

aFrontier

SK7 -0.68

-0.60

LUMO+2

-0.54

-1.47

-1.39

LUMO+1

-2.15

-2.20

-2.10

LUMO

-2.15

-2.53

-2.37

HOMO

-5.22

-4.79

-4.68

HOMO-1

-5.22

-5.25

-4.84

HOMO-2

-6.37

-5.28

-5.06

HOMO-3

-6.31

-5.39

HOMO-4

-6.42

-6.23

molecular orbitals for YD2 and SK7. Orbital energies are shown in unit of eV. 11 ACS Paragon Plus Environment


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Table 3. Time-dependent DFT results of YD2 and SK7.a YD2 State Energy (eV/nm)

f

SK7 MO Component

State Energy (eV/nm)

f

MO Component

S1

1.89 / 656

0.30 H → L (90%)

S1

1.92 / 646

0.08 H → L (89%)

S2

2.09 / 594

0.01 H → L+1 (73%)

S2

2.03 / 613

0.10 H-1 → L (57%)

S3

2.22 / 560

0.29 H-2 → L (44%)

H-1 → L (26%) S3

2.32 / 534

0.06 H-2 → L (76%) H-1 → L+1 (22%)

H → L+1 (29%) H-1 → L (24%)

S4

2.43 / 511

0.04 H-2 → L+1 (52%)

S4

2.33 / 532

H-1 → L (33%)

0.04 H-1 → L+1 (71%) H-3 → L (21%)

H → L+1 (14%) S5

2.95 / 421

1.25 H → L+2 (47%)

S5

2.45 / 506

H-1 → L+1 (33%) S6

3.03 / 409

0.03 H-2 → L+1 (70%) H-3 → L (26%)

0.67 H-2 → L+1 (42%)

S6

2.47 / 502

H-1 → L (36%)

0.62 H-2 → L (45%) H → L+1 (22%) H-3 → L+1 (21%) H-1 → L (11%)

S7

2.95 / 421

0.01 H → L+2 (87%)

S8

3.04 / 408

1.22 H-3 → L+1 (54%) H-1 → L+2 (22%)

S9

3.08 / 403

0.71 H-3 → L (43%) H-2 → L+1 (17%) H-1 → L+1 (16%)

S10

3.19 / 389

0.01 H-5 → L (67%) H-1 → L+2 (24%)

aH:

HOMO; L: LUMO; f: oscillator strength.


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2.5

Photovoltaic properties

Figure 7. (a) J-V Curves of SK7 and YD2 under one sun illumination, and (b) IPCE spectra of SK7 and YD2. The J-V characteristics of the devices based on SK7 and YD2 dyes under one sun illumination were shown in Figure 7a, where SK7 has shown JSC of 13.25 mA cm-2, VOC of 0.663 V, and FF of 0.745, which translate to a PCE of 6.54%. This PCE of SK7 is 16% lesser than that of YD2 (PCE of 7.78% with JSC of 15.42 mA cm-2, VOC of 0.694 V, and FF of 0.727), under similar test conditions. As can be seen in Table S3, the amount of dye loading on TiO2 surface for SK7 is nearly half to the amount that was loaded for YD2. The trend of dye loading for SK7 is consistent at different thickness levels of TiO2 layer (Table S3), when compared with the same of YD2 under similar immersion period. Figure 8 shows the box plots of photovoltaic parameters vs different thickness levels of TiO2 layer for the DSSCs fabricated by SK7 and YD2 dyes, under one sun illumination. As thickness of TiO2 layer reaches to 15 µm both the devices have shown maximum PCE values, which is also directly proportional to the amount of dye loading. Even though the dye loading for SK7 is nearly half of the amount to that of YD2, the corresponding device has still achieved 84% PCE to that was observed for YD2-based device. The incident photon-to-current conversion efficiency (IPCE) graphs for SK7- and YD2-based devices were shown in Figure 7b, where the IPCE profile echoes the trend that was noticed in UV-visible absorption spectrum, i.e., the 50 nm redshifted wavelength for YD2 over SK7. Though IPCE response of SK7 is blue shifted, its intensity between 380 and 650 nm is higher than that of YD2, this could be beneficial under artificial light illuminations (T5 or LED). Typical porphyrins such as YD2, shows a dip in 13 ACS Paragon Plus Environment


absorption between Soret and Q bands, as expected, such a dip is significantly mitigated in the case of SK7, thanks to the presence of split Soret band between 400 and 550 nm. The IPCE response of SK7 between 600 and 750 nm is weaker than that of YD2, which is consistent with its less intense Q-bands in UV-visible absorption profile (Figure 4) and less dye loading of SK7. Bearing aforementioned advantages and limitations, SK7-based device still manages to compete with YD2-based device, by means of PCE, under similar test conditions. Above-mentioned discussion indicates that device based on the novel dye SK7 shows relatively competitive performance with that of benchmark dye YD2.

Figure 8. Box plots of photovoltaic parameters vs Thickness of TiO2. (a) Current density vs Thickness of TiO2 (b) Voltage vs Thickness of TiO2 (c) Fill factor vs Thickness of TiO2 and (d) PCE vs Thickness of TiO2 layer under one sun illumination. 14 ACS Paragon Plus Environment

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Table 4. Photovoltaic parameters of devices based on SK7 and YD2 dyes, measured under 1.5G illumination. Dye Loading JSC VOC η JSC c FF -8 -2 b -2 (10 mol cm ) (mA cm ) (V) (%) (mA cm-2) 6.08 13.25 0.663 0.745 6.54 SK7 11.06 (±0.13) (±0.23) (±0.02) (±0.02) (±0.19) 9.48 15.42 0.694 0.727 7.78 YD2 13.06 (±0.02) (±0.13) (±0.00) (±0.00) (±0.06) a The device parameters shown here are with respective to the champion cells. b The thickness of Dye a,

TiO2 surface of the device parameters shown here is 15 µm, we also fabricated the devices with two more thickness levels of TiO2, i.e., 9 µm and 12 µm. The corresponding results were tabulated in Table S3, in Supporting Information. c JSC values were calculated from IPCE response.



Figure 9. Logarithmic dependence of (a) charge recombination resistance (b) capacitance and (c) electron lifetime at the open circuit potential of DSSCs based on SK7 and YD2. To understand the electron transport behavior of the devices at TiO2/dye/electrolyte interface, we are encouraged to test electrochemical impedance spectroscopy experiments. The devices were measured under dark condition and probed by a bias voltage in the range of 0.45 0.575 V. Raw EIS data were fitted with transmission-lined model64-65 and the inforamtion of interfacial charge recombination resistance (Rct), chemical capacitance (Cμ) and electron lifetime (τ0) can be obtained and then show in a logarithmic plot (Figure 9). It can be seen that YD2-based deivce has both higher Rct and Cμ than those of SK7-based device among the applied voltage range, resulting in higher τ0 based on the formula τ0 = Rct∙Cμ. Since both devices were composed of same materials except sensitizers, the different EIS parameters must come from the structure of the sensitizer. SK7 dye is designed to be bulky with two N,N-bis(4-hexylphenyl) amine moieties at two beta-positions, but undesired rigidness of zinc porphyrin ring jeopardises the adsorption amount on mesoporous TiO2 matrix. The loosely anchored SK7 could not form a satisfactory coverage on TiO2 surface and hence lead to severe recombination loss of photoelectrons with triiodide ions in the electrolyte.


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Figure 10. Photovoltaic parameters under dim light conditions. (a) JSC vs Illuminance (b) VOC vs Illuminance (c) PCE vs Illuminance and (d) Power input vs power output under T5 and LED light sources (300 – 6000 lux) for devices based on SK7 and YD2 dyes. 17 ACS Paragon Plus Environment


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Photovoltaic properties of SK7 and YD2 based devices under T5 and LED light sources (300 – 6000 lux) were tested. The corresponding J-V parameters were presented in Figure 10 and the data were tabulated in Table 5. Both the devices show maximum PCEs (ηmax) under 6000 lux intensity from T5 fluorescent tube or commercial LED lamp. The corresponding J-V curves were shown in Figure 11. The device based on SK7 has shown JSC of 0.739 mA cm-2, VOC of 0.584 and FF of 0.778 under T5 fluorescent tube at 6000 lux, which translate to a PCE of 19.7%, the cell with this PCE in turn will yield a Pout of 335 µW cm-2. These photovoltaic parameters of SK7 were in tight competition with that of benchmark dye YD2. It is worth noting that, excellent performances of DSSCs under several indoor light conditions are a function of how best the absorption wavelengths of the dyes used to fabricate the DSSCs match with the emission wavelengths of incident light sources used to measure the PCEs. Note that emission spectra of indoor light sources carry intense photon flux at visible region (Figure S3). In the case of SK7 dye, unlike under one sun it can absorb more photons under dim light, as it carries an additional Soret band at 450 – 550 nm, which will capture more photons from incident indoor light sources. As the result, the PCE of SK7-based device under T5 fluorescent lamp is equal to nearly 97% to that of YD2 (note that under 1 sun it is 84%). Interestingly, both the devices have also shown good performances under LED light source too. The PCEs of 15.5% (JSC = 0.613 mA cm-2, VOC = 0.582 and FF = 0.779) and 16.5% (JSC = 0.626 mA cm-2, VOC = 0.604 and FF = 0.785) were noted, for SK7 and YD2-based devices. As can be seen in Table 4, Table 5, the JSC values of SK7 (either under 1 sun or under LED light) is lower to that of YD2. This can be mainly attributed to poor dye loading on TiO2 surface, and partially due to the symmetry breakage of the direction of electrons driving from donor to acceptor within the molecule and weak absorption at Q-band region as a result poor IPCE response at longer wavelength region. It is expectable to increase the cell performance of SK7 over YD2, if the dye loading of SK7 on TiO2 reaches equal or nearly equal to that of YD2. The trends of PCEs under indoor light sources (T5 of LED) are directly proportional to the increase in the order of illuminance, i.e., the higher the illuminance the higher the PCE. This trend echoes to that was noted in existing literature.13-14, 53, 66-67 Table 5. Photovoltaic parameters under 6000 lx intensity of T5 fluorescent tube and commercial LED lamps for the devices based on SK7 and YD2 dyes. Dye a

JSC

VOC

FF 18

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η

Pout

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(mA cm-2)

(µW cm2) d SK7 b 0.739 (±0.002) 0.584 (±0.001) 0.778 (±0.002) 19.7 (±0.055) 335 (0) b YD2 0.721 (±0.000) 0.602 (±0.002) 0.783 (±0.003) 20.0 (±0.159) 340 (0) SK7 c 0.613 (±0.001) 0.582 (±0.002) 0.779 (±0.002) 15.4 (±0.096) 277 (0) c YD2 0.626 (±0.000) 0.604 (±0.002) 0.785 (±0.003) 16.5 (±0.135) 296 (0) a we tested the intensities of incident lights ranging between 300 and 6000 lux. b The parameters are under 6000 lux intensity from T5 fluorescent tube. c The parameters are under 6000 lux intensity from commercial LED lamp. d The Pin is 1.70 and 1.86 mW cm-2 for T5 fluorescent tube and commercial LED lamp, respectively, at 6000 lux of intensity. (V)

(%)

Figure 11. J-V curves of SK7, YD2 (under T5 and LED light sources at the illuminance of 6000 lux). 3

Conclusion We have successfully synthesized a novel dye named SK7 with two N,N-bis(4-

hexylphenyl)amino entities positioned at two beta-carbons. At first, we have synthesized beta-bisbrominated Zn porphyrin, followed by a Buchwald-Hartwig amination and a Sonogashira cross coupling reactions were performed in a sequential manner to get this novel dye. The N,N-bis(4hexylphenyl)amino units on beta-carbons has caused to slightly deviate the 24 atom mean plane of the porphyrin ring. This novel dye SK7 has showed a split Soret band between 400 and 550 nm, i.e. the dip between the Soret and Q bands is filled up, giving better light absorption capability. The device based on SK7 has achieved around 84% of the PCE when compared with that was achieved by benchmark dye YD2, under one sun illumination. Whereas, under T5 fluorescent tube the same device has achieved 97% of PCE when compared with that was achieved by YD2-based device, this highly competitive performance of SK7 under dim light is expectable as it carries split 19 ACS Paragon Plus Environment


Soret band between 400 and 550 nm, which would harvest additional photons of incident indoor light over YD2. It can be expected that the cell performance of SK7-related porphyrin dyes would be greatly enhanced as the dye adsorption on TiO2 is improved and this can be achieved by suitable modification of the SK7 structure. 4 4.1

Experimental section General information All the reagents were purchased from the available commercial sources and used without

any further purification unless otherwise noted. The solvents CH2Cl2, CHCl3, and CH3OH were dried using CaH2 and distilled freshly whenever required. The solvent THF was dried by using sodium/benzophenone method. The electrolyte tetrabutylammonium hexafluorophosphate ([(nBu)4N]PF6) was recrystallized twice from absolute ethanol and dried for 48 h under reduced pressure. Column chromatography was performed on silica gel with 70-230 mesh purchased from Merck. 1H and 13C NMR spectroscopic experiments were performed on a Varian spectrometer at the frequency of 400 MHz and 100 (or 150) MHz, respectively. The UV-visible absorption and emission spectra for porphyrins were measured at Varian Cary 50 spectrophotometer and JASCO FP-6000 spectrofluorometer, respectively. ESI mass spectra were recorded on a Bruker APEX II spectrometer (operating in the positive ion detection mode). The cyclic voltammetry experiments were measured on a three-electrode system consisting BAS glassy carbon (0.07 cm2) disk as working electrode, Ag/AgCl (saturated) as reference electrode and platinum wire as auxiliary electrode. The Ag/AgCl reference electrode was separated from the bulk solution by a double junction filled with an electrolyte solution (0.1M [(n-Bu)4N]PF6). The reported potentials are against Ag/AgCl and calibrated the accuracy of the potentials with respective to standard ferrocene/ferrocenium (Fc/Fc+) couple, which occurs at E1/2 = ca. +0.63 V vs Ag/AgCl. The glassy carbon working electrode was polished during each experiment freshly on a 0.03 μm alumina spread on Buehler felt pad and washed with deionized water and dry THF. The reproducibility of individual potential values were noticed to be within ±5 mV. 4.2

Synthetic procedures of SK7

Compound 3: In a three neck round bottom flask, di(1H-pyrrol-2-yl)methane (2) (1.8 g, 12.23 mmol) was dissolved in THF (28 mL), freshly prepared 1M EtMgBr (61.5 mL, 61.5 mmol, in dry 20 ACS Paragon Plus Environment

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THF) was added for 30 min at room temperature, and stirred for another 30 min. Freshly prepared 3,5-di-tert-butylbenzoyl chloride (1)49-51 (15.40 g, 61.5 mmol) in THF (14 mL) was then added dropwise to the above reaction vessel for 30 min at room temperature, and stirred for another 45 min. The reaction mixture was quenched with saturated NH4Cl solution at 0 oC. The quenched solution was extracted with CH2Cl2 and the organic layer was dried using anhydrous MgSO4, the volatile solvents were removed under reduced pressure. The crude compound was subjected to silica gel column chromatography eluting with CH2Cl2:EtOAc (9.6:0.4, v/v) to yield compound 3 (1.89 g, 54%, white solid). 1H NMR (400 MHz, CDCl3): δ 10.29 (bs, 2H, NH), 7.70 (d, 4H, J = 2.0 Hz, phenyl-2-H), 7.60 (t, 2H, J = 2.0 Hz, phenyl-4-H), 6.75 (dd, J = 2.4 Hz, 2H, pyrrole-3-H), 6.20 (dd, J = 2.6 Hz, 2H, pyrrole-4-H) 4.18 (br, 2H, CH2), 1.34 (s, 36H, C(CH3)3; 13C NMR (100 MHz, CDCl3): δ 185.80, 150.85, 138.14, 137.13, 131.55, 125.88, 123.73, 121.07, 110.30, 35.15, 31.60 ; ESI-HRMS: m/z calcd for C39H50N2O2 578.3872, found 579.3943 [M+1]+. Compound 4: In a three neck round bottom flask was taken compound 2 (1.2 g, 2.07 mmol) in CHCl3 (30 mL), a nitrogen balloon was equipped, and liquid bromine (0.20 mL, 3.98 mmol, 1.92 eq) was added dropwise at 0 oC. This reaction mixture was quenched within 15 min by using cold water. The resulting solution was extracted with the CH2Cl2, and washed with NaHCO3 and Na2S2O3, sequentially. The collected organic layer was dried using anhydrous MgSO4 and concentrated to dryness under reduced pressure, beige colored crude compound was recrystallized with CH2Cl2 and CH3OH to get required compound 4 (1.4 g, 45.8%). 1H NMR (400 MHz, CDCl3): δ 11.33 (br, 2H, Py-NH), 7.62 (br, 4H, phenyl), 7.59 (br, 2H, phenyl), 6.68 (d, J = 2 Hz, 2H), 4.24 (s, 2H, py-CH2-py), 1.31 (s, 36H, C(CH3)3);

13C

NMR (100 MHz): δ 185.91, 150.99,150.82,

138.08, 137.34, 131.51, 130.73, 125.93, 123.85, 121.20, 110.37, 35.14, 31.60; ESI-HRMS: m/z calcd for C39H48Br2N2O2 734.2082, found 735.2159 [M+1]+. Compound 7 and 8: In a three neck round bottom flask, compound 4 (0.4 g, 0.54 mmol) in THF (26 mL) and methanol (9 mL) was taken and maintained inert atmosphere. Sodium borohydride (1.02 g, 27.15 mmol) was added portion wise into the reaction mixture for 30 minutes at 0 0C. The resulting solution was stirred for 30 minutes at room temperature. The TLC shows absence of diketone 4 and formation of di-alcohol 5. The reaction mixture was quenched by using saturated NH4Cl solution, and the di-alcohol 5 was extracted with CH2Cl2. The organic layer was dried using anhydrous MgSO4 and evaporated to dryness under reduced pressure. This crude di-alcohol 5, 21 ACS Paragon Plus Environment


along with compound 6 (0.176 g, 0.540 mmol) was degassed for 15 min, and taken into two-neck round bottom flask. Freshly dried acetonitrile (216 mL) was added to the reaction mixture, and the TFA (0.524 mL, 6.858 mmol) was added dropwise under dark condition. This solution was stirred for 15 minutes and DDQ (0.367 g, 1.62 mmol) was added. The resulting suspension was stirred for another one hour. Triethylamine (5mL) was added to quench TFA, and the solvent was evaporated under reduced pressure and pass through short plug silica gel column to get crude free base porphyrin 7. The crude compound was metallated using Zn(OAc)2 (10 eq). After metalation, the solvent was removed under reduced pressure and the crude compound was subjected to silica gel column chromatography eluting CH2Cl2:hexane (1:2, v/v) to yield compound 8 (50 mg, 11.5%, overall yield for three steps). 1H NMR (400 MHz, CDCl3): δ 10.44 (s, 1H, meso-position), δ 9.80 (d, J = 4.4 Hz, 2H, β-position), δ 9.029 (s, 2H, β-position,), δ 9.00 (d, J = 4.8 Hz, 2H, β-position), 8.01 (d, 4H, J = 1.6, meso-phenyl), δ 7.83 (t, J = 1.6 Hz, 2H, meso-phenyl), δ 1.55 (m, 36H, C(CH3)3), δ 1.43 (m, 21H, isopropyl-H); 13C NMR (100 MHz, CDCl3): δ δ 153.21, 149.15, 146.09, 140.95, 133.93, 133.26, 131.63, 129.62, 123.10, 121.87, 121.62, 114.97, 109.41, 102.58, 101.47, 35.31, 32.01, 29.93, 19.34, 12.13; ESI-HRMS: m/z calcd for C59H70Br2N4SiZn, 1086.3007, found 1089.4000 [M+1]+. Compound 10: In a three neck round bottom flask under inert atmosphere was taken compound 10 (0.160 g 0.147 mmol), Pd(OAc)2 (0.013 g, 0.058 mmol), DPEPhos (0.039 g, 0.073 mmol), 60% NaH (0.141 g, 5.916 mmol), and dry diarylamine (0.496 g 1.47 mmol). The components were degassed for 15 min, and equipped with N2 balloon, dry THF (5 mL) was added to this reaction vessel. Stirred the resulting suspension for 5 hours under refluxing temperature. The TLC shows clear conversion of starting material to product, and cooled the reaction to room temperature and filtered the solids through celite pad. The filtrate was concentrated under reduced pressure and subjected to silica gel column chromatography CH2Cl2:hexanes (1:3, v/v) to yield required diamine 10 (0.190 g, 41%,). 1H NMR (400 MHz, CDCl3): δ 9.80 (s, 1H, meso-position), 9.68 (d, J = 4.8 Hz, 2H, β-position), 8.91 (d, J = 4.4 Hz, 2H, β-position), 8.25 (s, 2H, β-position), 7.92 (d, J = 2 Hz, 4H, meso-phenyl), 7.63 (s, 2H, meso-phenyl-p-position), 7.13 (d, J = 8.4 Hz, 8H, Nphenyl), 6.99 (d, J = 8.4 Hz, 8H, N-phenyl), 2.49 (t, J = 7.6 Hz, 2H, N-phenyl-p-hexyl-CH2), 1.511.28 (m, 66H, N-phenyl-p-hexyl; 36H, C(CH3)3), 0.89 (t, J = 6.8 Hz, 12H, N-phenyl-p-hexylCH3). 13C NMR (150 MHz, CDCl3): δ 151.98, 151.43, 150.18, 149.70, 148.66, 147.35, 144.64, 141.21, 141.17, 137.34, 135.36, 132.49. 130.34, 129.75, 129.10, 128.94, 123.78, 123.49, 122.15, 22 ACS Paragon Plus Environment

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120.67, 117.76, 109.66, 102.38, 99.91, 96.96, 35.43, 35.21, 34.94, 31.75, 31.73, 31.69, 31.67, 31.57, 29.69, 29.23, 29.99, 22.65, 22.63, 19.13, 14.13, 14.11, 11.91; ESI-HRMS: m/z calcd for C107H138N6SiZn, 1600.0077, found 1601.2005 [M+1]+. FTIR (ATR) νmax: 2949, 2869, 2144, 1695, 1595, 1501, 1461, 1288, 1001, 797, 711 cm-1. SK7: In a single neck round bottom flask, compound 10 (0.085 g, 0.053 mmol) was taken in dry THF (8 mL) and degassed for 5 min then equipped with N2 balloon. To this solution 1M TBAF (0.069 g, 0.265 mmol) was added and stirred for 15 minutes. The solution was quenched with water and extracted into CH2Cl2. The organic layer was dried using anhydrous MgSO4, and the volatile solvents were evaporated to dryness under reduced pressure. The crude compound along with Pd2(dba)3 (0.0049 g, 0.0054 mmol), AsPh3 (0.016 g, 0.0530 mmol), 4-iodobenzoic acid (0.065 g, 0.265 mmol) were taken into schlenk flask, and degassed for 10 min. A N2 balloon was equipped and dry THF:NEt3 (9:1, v/v) was added to the reaction mixture and stirred the suspension for 3 hours at refluxing temperature. The solids were filtered through short-plug celite pad and evaporated the volatile solvents to dryness under reduced pressure. The crude compound was subjected to silica gel column chromatography eluting with CH2Cl2:CH3OH (19:1, v/v) to get the title compound SK7 (50 mg, 62%). 1H NMR (400 MHz, CDCl3): δ 9.81 (s, 1H, meso-position), 9.71 (d, J = 4.8 Hz, 2H, β-position), 8.96 (d, J = 4.4 Hz, 2H, β-position), 8.25 (s, 2H, β-position), 8.24 (d, J = 8.4 Hz, 2H, phenylethynyl), 8.09 (d, J = 8.4 Hz, 2H, phenylethynyl), 7.95 (d, J = 1.6 Hz, 4H meso-phenyl-o-position), 7.65 (s, 2H, meso-phenyl-p-position), 7.14 (d, J = 8 Hz, 8H, Nphenyl), 7.00 (d, J = 8 Hz, 8H, N-phenyl), 2.50 (t, J = 7.6 Hz, 8H, N-phenyl-p-hexyl-CH2), 1.59 – 1.29 (m, 36H, N-phenyl-p-hexyl; 36H, C(CH3)3), 0.90 (t, J = 6.8 Hz, 12H, N-phenyl-p-hexyl); 13C NMR (150 MHz, CDCl3): δ 170.44, 151.69, 150.18, 148.77, 147.36, 144.62, 141.06, 137.47,132.68, 131.34, 130.39, 130.01, 129.30, 128.98, 128.29, 125.01, 123.85, 123.42, 122.55, 120.72, 117.75, 102.79, 98.56, 96.82, 95.04,35.44, 34.97, 31.73, 31.69, 31.57, 29.69, 29.24, 22.65, 14.13; ESI-HRMS: m/z calcd for C105H122N6O2Zn, 1563.8954, found 1563.8992 [M+1]+. FTIR (ATR) νmax: 3018, 2970, 1740, 1505, 1367, 1215, 1077 cm-1. 4.3

Device fabrication

In the section of device fabrication process, all material and reagents were purchased from available commercial sources and were almost 99% pure. The standard protocol of device fabrication was implemented, which started with the cleaning process of the transparent 23 ACS Paragon Plus Environment


conducting glass (FTO) by super-sonicating with detergent, deionized water, and acetone sequentially. The general DSC device consists of a TiO2 deposited photoanode and a platinum-covered counter electrode sealed together by a piece of hot melt adhesive film known as Surlyn. In the preparation for photoanode, a nanocrystalline transparent TiO2 film (using Ti-2105 paste bought from Eternal Co, Taiwan) and a scattering layer (using Ti-2325 paste bought from Eternal Co. Taiwan) with moderate thickness were deposited in sequence by screen-printing onto a clean fluorine doped tin oxide (3.1 mm thick, 13 Ω/square, 8% haze). The TiO2 covered photoanode was progressively sintering at elevated temperature up to 500 oC, sustained for 30 minutes, and then cooling down to the ambient temperature. The active area of TiO2 film is 0.16 cm2. After post-treatment with 40 mM TiCl4 solution at 70 oC for 30 minutes, the photoanode was annealed at 450 oC for 30 minutes. After cooling down to the room temperature, the TiO2 film was then dipped into the porphyrin solution for 2 hrs to let the dye adherence on to the film. The sensitized photoanode was well prepared after removing the saturate dye-attached anode in succession with ethanol rinsing and keeping dry by air gun flow. On the other hand, the platinum-deposited photocathode was prepared by two-step dip coating method as interpreted that, a fluorine-doped tin oxide glass (2.2 mm thick, 8Ω/square) was immersed into the surfactant agent at 70 oC for 5 minutes, then poly-N-vinyl-2pyrrolidone-capped platinum nanocluster dispersion (PVP-Pt) at 45 oC for 5 minutes in sequence and then rinsed by the deionized water. Subsequently, the already platinum-covered substrate was sintered at 325 oC for 30 minutes. The preceding work for preparing the PVP-Pt nanocluster dispersion was reported in previous study.68-69 The sandwich-type DSC device was assembled by sealing a piece of already dye-loaded photoanode and a piece of platinum deposited counter electrode together with a hot melt film (Surlyn, 30μm) at 120 °C and then injecting the wellprepared electrolyte into the hole-drill on the counter electrode side. In order to avoid the electrolyte leakage problem, a feasible encapsulation method was used by sealing the electrolyte injection hole with the Surlyn sheet and a thin glass sheet at high temperature of 120 °C. The dye solution with molar concentration of 0.15 mM was prepared by dissolving porphyrin into the mixture of 1:1 tetrahydrofuran and ethanol (v/v) and then adding the 0.3 mM chenodeoxycholic acid (CDCA) as co-adsorbent into the dye solution. The shielding mask of 0.36 cm2 was attached on the illuminating side of the device. The electrolyte consisted of 0.07M LiI, 1M PMII, 0.05M I2, 0.05M TBP in acetonitrile/valeronitrile (85:15, v/v). 24 ACS Paragon Plus Environment

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4.4

Device characterization under one sun and EIS measurement

In this study, the photovoltaic characteristics of DSC device under AM 1.5 G solar irradiation (intensity of 100 mW cm-2) were measured by the solar simulator machine (PEC-L15, Peccell Technologies, Inc. Yokohama, Japan) equipped with 700 W short-arc Xenon lamp as the illuminating source and the computer-controlled digital source meter (Keithley 2400C) as currentvoltage interpreter. Concerning the calibration of light-intensity, a Si-KG3 filtered solar cell as reference cell was used. The incident photon-to-current conversion efficiency (IPCE) measurement was conducted by using IPCE machine (PEC-S20, Peccell Technologies, Inc. Yokohama, Japan), which was equipped with monochromatic light illumination from 150 W Xenon lamp. The Si photodiode cell (S1337-1010BQ) as reference cell was used for spectral calibration. The EIS measurements were operated by employing a computer-controlled electrochemical interface workstation (Schlumberger SI-1286) combined with a HF frequency response analyzer (Schlumberger SI-1255). The frequency range was set up from 100 kHz to 0.1 Hz and the AC amplitude as 10 mV. During the EIS measurment, the DSC device was placed under the dark environment and the impedance data were simultaneously recorded as the function of applied DC bias ranged from 0 V to X V equivalent to the open-circuit voltage of DSCs. The data were then compiled and fitted by Z-View software in employment with a relevant equivalent circuit. 4.5

Device characterization under dim light

In this section of J-V characteristics under dim light environment, a customized instrument equipped with a mobile elevated platform, which was enclosed around with black shade curtain was used. About the inside part of the instrument, an upper stage placed with an exchangeable light fixture, could be manually height-controllable. The indoor lightning resource are T5 fluorescent lamp (FH14D-EX/T, China Electric Mfg Corporation, Taiwan) and LED-planar (FOP/A/40W/757/U/ 2Χ2, EVERLIGHT). The bottom platform was embedded with a calibrated spectroradiometer (ISM-Lux, Isuzu Optics, Japan). In the preceding work, the light calibration has already conducted for the precise detection of incident light intensity. The required set of the incident light intensity could be achieved by tuning the height of light fixture, equipped to the appropriate position. Afterward, the DSC device was put close to the calibrated spectroradiometer, 25 ACS Paragon Plus Environment


then the I-V measurment was conducted and interpreted by the digital source meter (Keithley 2400C) associated with the program-installed PC.

Conflict of interest The authors declare no conflict of interest. Acknowledgements C.-Y.Y. is grateful for the financial support for this work from the Ministry of Science and Technology (MOST) in Taiwan with Grant No. MOST 107-2113-M-005-010-MY3, and the “Innovation and Development Center of Sustainable Agriculture” from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan. T.-C.W. is grateful for the financial support for his work from the MOST in Taiwan with grant No. MOST 106-2119-M-007-025-MY3 and MOST 1052628-E-007-012-MY3. Supporting information The supporting information was included with synthetic procedures of intermediates, extended scientific figures, and tables that supports the main text of the article.


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5

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Synthesis and Characterization of Novel Î²-Bis(N,N-diarylamino

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