Naphtho[2,3-c][1,2,5]thiadiazole and 2H-Naphtho[2 ... - ACS Publications

Subscriber access provided by UNIV OSNABRUECK

Article

Naphtho[2,3-c][1,2,5]thiadiazole and 2H-Naphtho[2,3-d][1,2,3]triazoleContaining D–A–#–A Conjugated Organic Dyes for Dye-Sensitized Solar Cells Yung-Sheng Yen, Jen-Shyang Ni, Wei-I Hung, Chih-Yu Hsu, Hsien-Hsin Chou, and Jiann-T'suen Lin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b00806 • Publication Date (Web): 19 Feb 2016 Downloaded from http://pubs.acs.org on February 23, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38

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

ACS Applied Materials & Interfaces

Naphtho[2,3-c][1,2,5]thiadiazole and 2HNaphtho[2,3-d][1,2,3]triazole-Containing D–A–π–A Conjugated Organic Dyes for Dye-Sensitized Solar Cells Yung-Sheng Yen,* Jen-Shyang Ni, Wei-I Hung, Chih-Yu Hsu, Hsien-Hsin Chou, Jiann-T′suen Lin Institute of Chemistry, Academia Sinica, 115 Nankang, Taipei, Taiwan. KEYWORDS: dye-sensitized solar cells, organic sensitizer, Naphtho[2,3-c][1,2,5]thiadiazole, 2H-Naphtho[2,3-d][1,2,3]triazole, D–A–π–A

ABSTRACT: Dipolar dyes comprising an arylamine as the electron donor, a cyanoacrylic acid as electron acceptor, and an electron deficient naphtho[2,3-c][1,2,5]thiadiazole (NTD) or naphtho[2,3-d][1,2,3]triazole (NTz) entity in the conjugated spacer, were developed and used as the sensitizers in dye-sensitized solar cells (DSSCs). The introduction of the NTD unit into the molecular frame distinctly narrows the HOMO/LUMO gap with electronic absorption extending to >650 nm. However, significant charge trapping and dye aggregation were found in these dyes. Under standard global AM 1.5 G illumination, the best cell photovoltaic performance achieved

ACS Paragon Plus Environment

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

Page 2 of 38

6.37% and 7.53% (~94% relative to N719-based standard cell) without and with CDCA coadsorbent, respectively. Without CDCA, the NTz dyes have higher power conversion efficiency (7.23%) than NTD dyes due to less charge trapping, dye aggregation and better dark current suppression.

Introduction Since the innovative report by Grätzel and co-worker in 1991,1 dye-sensitized solar cells (DSSCs) have attracted considerable attention due to their low cost of production, high incident solar light to electricity conversion efficiency and facile cell fabrication. Among the components used in DSSCs, the sensitizer definitely plays a very critical role in the device performance. Quite a few DSSCs sensitized by polypyridyl Ru(II) complexes have achieved remarkably high conversion efficiencies exceeding 11% under air mass (AM) 1.5 illumination.2-6 More recently, porphyrin-based DSSCs have achieved a record high efficiency of 13.0%, which surpasses that of ruthenium dyes-based DSSCs.7 These two types of dyes are of high cost and/or hard to purify. In comparison, metal-free dyes are of lower cost and more flexible in molecular design. Moreover, the intense optical absorption of metal-free dyes is advantageous for solid state DSSCs because thinner TiO2 film is needed to facilitate electron transport. This characteristic also benefits fabrication of co-sensitized DSSCs with metal-free dyes absorbing in the complementary spectral regions.8-11 Considerable progress has been made on metal-free organic dye sensitizers12-20 and impressively high efficiency over 14% has been achieved.21 A typical organic dye has a donor–π bridge–acceptor (D–π–A) skeleton, which exhibits an intramolecular charge-transfer (ICT) transition from the donor to the acceptor upon


2

Page 3 of 38

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


photoirradiation. In order to broaden the absorption spectra of the sensitizers in the visible and near-IR region, D–A–π–A type dyes with an additional electron-accepting group in the conjugated spacer is an efficient approach for red shifting the absorption spectra.22-23 The D–A– π–A configuration not only is instrumental to modulate the absorption spectra, but also improves the photovoltaic performances and stability of organic sensitizers. In our earlier report, we developed metal-free sensitizers with an electron-deficient benzothiadiazole (BT) unit in the conjugated spacer,24 and found that the BT unit effectively shifted the electronic absorption band to a longer wavelength. However, the efficiency was far from satisfactory, and the best photonto-electricity conversion efficiency of the DSSCs reported only reached ~70% of the standard cell based on cis-Ru(NCS)2(dcbpy) (dcbpy = 2,2′-bipyridyl-4,4′-dicarboxylate). Later, we25 and others26-32 found that much improved efficiencies could be achieved with BT-based sensitizers after appropriate modification of the conjugated spacer. We and others also found that replacement of the BT unit by a less electron deficient benzotriazole (BTz) unit improved the power conversion efficiencies.33-36 Based on the D–A–π–A dyes developed in our group with different

elecron

deficient

entities

such

as

BT,24,25

BTz,36

cyanovinyl

entity,37

pyrido[2,1,3]thiadiazole38 and 2H-[1,2,3]triazolo[4,5-c]pyridine,39 we found that the Mulliken charges of the second acceptor in the S0 → S1 transition was an useful semi-empirical index for the electron injection efficiency of the dye molecule and the cell efficiency as well, i.e., the cell efficiency drops as the Mulliken charge of elecron deficient entity goes more negative. Fused-heteroaromatic acenes are popularly used for electronic devices due to their fascinating optical and electronic properties.40 Compared with benzothiadiazole (BT) and benzotriazole (BTz), naphtho[2,3-c][1,2,5]thiadiazole (NTD) and 2H-naphtho[2,3-d][1,2,3]triazole (NTz) have an additional benzene ring fused in the skeleton and have a narrower HOMO/LUMO gap (Figure


3


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 4 of 38

S1). NTD entity has been used for organic light-emitting diodes41-43 and organic thin film transistors44 due to its good ambipolar transporting property. To our knowledge, both NTD and NTz have not been used for the sensitizers of DSSCs yet. In continuation of our studies on D–A– π–A type dyes, we decided to incorporate NTD and NTz units in the conjugated spacer as the second electron acceptor. Therefore, we conducted a systematic study on the NTD- and NTzbased sensitizers for DSSC applications. Herein we report the synthesis, physical properties and DSSC performance of new dyes based on NTD and NTz.

EXPERIMENTAL DETAILS Materials and instruments. All chemicals were obtained from Alfa Lancaster, Acros and Aldrich. The solvents were dried over sodium or CaH2 and distilled before use. Unless otherwise specified, all the reactions were performed under nitrogen atmosphere using standard Schlenk techniques. TiO2 paste was purchased from Solaronix S. A., Switzerland. 1

H NMR spectra were recorded on a Bruker 300-MHz, 400-MHz or 500-MHz spectrometer.

Absorption spectra were recorded on a Cary 50 probe UV-Vis spectrophotometer. All chromatographic separations were carried out on silica gel (60M, 230-400 mesh). Mass spectra (FAB) were recorded on a VG70-250S mass spectrometer. Elementary analyses were performed on a Perkin-Elmer 2400 CHN analyzer

Synthesis of 1a. In a 100 mL flask,1,4-dibromo-2,3-diaminonaphthalene (3.500 g, 11.08 mmol) is dissolved in 46 mL of anhydrous pyridine and then 2.62 mL (23.3 mmol) of thionylaniline and 14.0 mL (111 mmol) of chlorotrimethylsilane are added. The reaction was heated at 80 °C overnight with stirring. After cooling the reaction to room temperature, 20 mL of


4

Page 5 of 38

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


ethanol is added to the mixture. The precipitate is filtered, washed with ethanol and then recrystallized from a mixture of ethanol and chloroform to give orange needles. (2.97 g, yield: 70%). 1H NMR (400 MHz, CDCl3): δ 8.40 (2H, dd, J = 7.2 Hz, 3.2 Hz), 7.59 (2H, dd, J = 7.2 Hz, 3.2 Hz). 13C NMR (100 MHz, CDCl3): δ 149.8, 132.8, 128.6, 128.1, 127.7, 126.9, 112.0.

Synthesis of 1b. To a solution of 1,4-dibromo-2,3-diaminonaphthalene (3.16 g, 10.0 mmol) in 30 mL of AcOH, was added a solution of NaNO2 (3.0 g, 33.0 mmol) in 15 mL of H2O. The mixture was stirred for another 20 min at room temperature, the precipitate obtained was collected by filtration and washed with water to afford 4,9-dibromo-1H-naphtho[2,3d][1,2,3]triazole (NTz) as brown powder. The crude was used as such without further purification. 4,9-dibromo-1H-naphtho[2,3-d][1,2,3]triazole (NTz) (2.53 g, 7.74 mmol) was dissolved in DMF (30 mL), and with rapid stirring under nitrogen was added triethylamine (1.25 mL, 8.9 mmol) over 5-10 min. After stirring for 1 h, 1-bromohexane (1.25 mL, 8.9 mmol) was added dropwise. The reaction was allowed to stir at room temperature for 12 h. On completion of the reaction, the DMF was removed under reduced pressure and extracted with DCM (3 × 100 mL). The organic layers were combined and dried using MgSO4 and finally purified by column chromatography using a dichloromethane/hexane mixture as the eluent. 1H NMR (CDCl3, 400 MHz): δ 8.35 (dd, J = 7.2 Hz, 3.3 Hz, 2H), 7.52 (dd, J = 7.2 Hz, 3.3 Hz, 2H), 4.91 (t, J = 7.5 Hz, 2H), 2.28-2.18 (m, 2H), 1.44-1.28 (m, 6H), 0.87 (t, J = 7.2 Hz, 3H).

13

C NMR (CDCl3, 100

MHz): δ 142.1, 130.7, 126.5, 126.4, 108.2, 57.9, 30.9, 30.0, 26.0, 22.1, 13.7. MS (FAB) m/z : 410.20 (M+). Anal. Calcd for C16H17Br2N3: C, 46.74; H, 4.17; N, 10.22. Found: C, 46.65; H, 4.10; N, 10.15.


5


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 6 of 38

Synthesis of 2a. A mixture of 1a (0.94 g, 2.73 mmol) and 4-(hexyloxy)-N-(4(hexyloxy)phenyl)-N-(4-(tributylstannyl)phenyl)aniline (2.0 g, 2.74 mmol), PdCl2(PPh3)2 (0.02 g, 0.03 mmol) and dry DMF were loaded into a two-necked flask under nitrogen atmosphere and stirred overnight at 80 oC. After cooling, it was quenched with aqueous KF and extracted with diethyl ether. The organic extracts were washed with brine and dried over anhydrous MgSO4. The crude product was purified by column chromatography using a dichloromethane/hexane mixture as the eluent. 1H NMR (CDCl3, 400 MHz): δ 8.41 (d, J = 9.0, 1 H), 8.12 (d, J = 9.0 Hz, 1H), 7.56-7.51 (m, 1H), 7.39 (d, J = 8.4 Hz, 2H), 7.38-7.34 (m, 1H), 7.18 (d, J = 8.8 Hz, 4H), 7.07 (d, J = 8.4Hz, 2H), 6.86 (d, J = 8.8 Hz, 4H), 3.93 (t, J = 6.6 Hz, 4H), 1.79-1.72 (m, 4H), 1.47-1.27 (m, 12H), 0.91-0.87 (m, 6H).

13

C NMR (CDCl3, 100 MHz): δ 155.8, 151.0, 150.9,

148.9, 140.0, 132.8, 132.1, 131.9, 131.1, 128.0, 127.7, 127.3, 127.1, 126.2, 118.4, 115.3, 110.3, 68.1, 31.5, 29.2, 25.6, 22.5, 13.9. FAB-HRMS calcd for C40H42BrN3O2S: 708.2175, Found: 708.2159.

Synthesis of 2b. It was synthesized by the same procedure as described above for 2a. 1H NMR (CDCl3, 400 MHz): δ 8.43 (d, J = 8.8 Hz, 1H), 8.10 (d, J = 8.8 Hz, 1H), 7.56 (dd, J = 8.4 Hz, 5.6 Hz, 1H), 7.46 (d, J = 8.4 Hz, 2H), 7.39 (dd, J = 8.4 Hz, 5.6 Hz, 1H), 7.31 (t, J = 8.0 Hz, 4H), 7.25-7.23 (m, 6H), 7.08 (t, J = 8.0 Hz, 2H). MS (FAB) m/z : 508.1 (M+).

Synthesis of 2c. It was synthesized by the same procedure as described above for 2a. 1H NMR (CDCl3, 500 MHz): δ 8.37 (d, J = 10.0 Hz, 1H), 8.19 (d, J = 10.0 Hz, 1H), 7.49 (d, J = 10.0 Hz, 2H), 7.48-7.45 (m, 1H), 7.31 (t, J = 10.0 Hz, 1H), 7.21 (d, J = 10.0 Hz, 4H), 7.11 (d, J = 10.0 Hz, 2H), 6.89 (d, J = 10.0 Hz, 4H), 4.87 (t, J = 5.0 Hz, 2H). 3.94 (t, J = 5.0 Hz, 4H), 2.23-2.17 (m,


6

Page 7 of 38

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


2H), 1.82-1.76 (m, 4H), 1.50-1.28 (m, 18H), 0.98-0.95 (m, 9H). 13C NMR (CDCl3, 75 MHz): δ 155.8, 148.6, 143.0, 142.3, 140.2, 131.8, 131.0, 130.5, 128.5, 127.2, 127.0, 126.4, 126.3, 124.6, 118.8, 115.3, 106.3, 68.1, 57.7, 31.5, 31.1, 30.2, 29.2, 26.2, 25.7, 22.5, 22.3, 13.9, 13.8. FABHRMS calcd for C46H55BrN4O2: 774.3505, Found: 774.3566.

Synthesis of 3a. A mixture of 2a, 2-tributylstannyl-5-dioxolanyl thiophene, PdCl2(PPh3)2 and dry DMF was heated to 85 oC for 8 h. After cooling, it was quenched with aqueous KF and extracted with diethyl ether. The organic extracts were washed with brine and dried over anhydrous MgSO4. The resulting dioxolane derivative was suspended in glacial acetic acid (15 mL) and heated to 50 ºC. After a clear solution is formed 1 mL of water was added and maintained at 50 ºC for 5 h. The crude product was purified by column chromatography using a dichloromethane/hexane mixture as the eluent to give 3a. 1H NMR (CDCl3, 300 MHz): δ 10.03 (s, 1H), 8.22-8.18 (m, 2H), 7.97 (d, J = 4.0 Hz, 1H), 7.55 (d, J = 4.0 Hz, 1H), 7.45 (d, J = 8.8 Hz, 2H), 7.42-7.34 (m, 2H), 7.19 (d, J = 8.8 Hz, 4H), 7.08 (d, J = 8.8 Hz, 2H), 6.87 (d, J = 8.8 Hz, 4H), 3.94 (t, J = 6.6 Hz, 4H), 1.82-1.73 (m, 4H), 1.48-1.33 (m, 12H), 0.92-0.89 (m, 6H).

13

C

NMR (CDCl3, 75 MHz): δ 182.9, 156.0, 151.3, 147.1, 145.0, 140.0, 136.1, 132.0, 131.7, 131.2, 127.9, 127.7, 127.5, 126.1, 126.0, 119.7, 118.4, 115.4, 68.2, 31.6, 29.3, 25.7, 22.6, 14.0. MS (FAB) m/z : 739.20 (M+). FAB-HRMS calcd for C45H45N3O3S2: 739.2898, Found: 739.2864.

Synthesis of 3b. It was synthesized by the same procedure as described above for 3a. 1H NMR (CDCl3, 300 MHz): δ 10.16 (s, 1H), 8.18 (dd, J = 6.9 Hz, 3.6 Hz, 1H), 8.12 (d, J = 8.2 Hz, 2H), 7.89 (dd, J = 6.9 Hz, 3.6 Hz, 1H), 7.82 (d, J = 8.2 Hz, 2H), 7.46 (d, J = 8.4 Hz, 2H), 7.387.33 (m, 2H), 7.20 (d, J = 8.2 Hz, 4H), 7.10 (d, J = 8.4 Hz, 2H), 6.87 (d, J = 8.2 Hz, 4H), 3.94 (t,


7


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

J = 6.6 Hz, 4H), 1.82-1.73 (m, 4H), 1.48-1.32 (m, 12H), 0.92-0.90 (m, 6H).

Page 8 of 38

13

C NMR (CDCl3,

75 MHz): δ 182.3, 157.5, 155.4, 152.8, 152.5, 150.3, 143.1, 141.5, 132.1 132.0, 131.7, 129.8, 127.7, 127.4, 127.0, 126.2, 126.0, 118.6, 115.4, 68.3, 31.6, 29.3, 25.7, 22.6, 14.0. MS (FAB) m/z : 732.80 (M +−1). FAB-HRMS calcd for C47H47N3O3S: 733.3335, Found: 733.3362.

Synthesis of 3c. It was synthesized by the same procedure as described above for 3a. 1H NMR (CDCl3, 400 MHz): δ 10.06 (s, 1H), 8.22 (d, J = 8.0 Hz, 1H), 8.16 (d, J = 8.0 Hz, 1H), 7.97 (d, J = 3.6 Hz, 1H), 7.56 (d, J = 3.6 Hz, 1H), 7.51 (d, J = 8.4 Hz, 2H), 7.48-7.38 (m, 2H), 7.32 (t, J = 8.0 Hz, 4H), 7.30-7.25 (m, 6H), 7.09 (t, J = 8.0 Hz, 2H). MS (FAB) m/z : 539.1 (M+).

Synthesis of 3d. It was synthesized by the same procedure as described above for 3a. 1H NMR (CDCl3, 300 MHz): δ 10.06 (s, 1H), 8.42 (d, J = 8.7 Hz, 1H), 8.32 (d, J = 8.7 Hz, 1H), 7.96 (d, J = 3.6 Hz, 1H), 7.68 (d, J = 3.6 Hz, 1H), 7.59 (d, J = 8.4 Hz, 2H), 7.46-7.34 (m, 2H), 7.27 (d, J = 8.7 Hz, 4H), 7.18 (d, J = 8.4 Hz, 2H), 6.95 (d, J = 8.7 Hz, 4H), 4.87 (t, J = 6.9 Hz, 2H), 4.00 (t, J = 6.3 Hz, 4H), 2.23-2.18 (m, 2H), 1.87-1.70 (m, 4H), 1.54-1.36 (m, 18H), 1.03-0.99 (m, 9H). 13C NMR (CDCl3, 75 MHz): δ 182.6, 155.7, 148.6, 147.3, 144.1, 142.4, 142.2, 140.0, 136.2, 131.8, 130.6, 130.5, 130.3, 129.6, 127.1, 126.4, 125.9, 125.1, 124.3, 118.6, 116.4, 115.2, 68.0, 57.4, 31.4, 30.9, 29.9, 29.1, 27.7, 26.6, 26.0, 25.6, 22.4, 22.2, 17.4, 13.9. MS (FAB) m/z : 806.2 (M +

−1). FAB-HRMS calcd for C51H58N4O3S: 806.4225, Found: 806.4259.

Synthesis of 3e. It was synthesized by the same procedure as described above for 3a. 1H NMR (CDCl3, 400 MHz): δ 10.19 (s, 1H), 8.14 (d, J = 8.0 Hz, 2H), 8.07-8.05 (m, 1H), 7.95 (d, J = 8.0 Hz, 2H), 7.62 (d, J = 8.4 Hz, 2H), 7.36-7.33 (m, 2H), 7.28 (d, J = 8.8 HZ, 4H), 7.20 (d, J = 8.4


8

Page 9 of 38

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


Hz, 2H), 6.95 (d, J = 8.8 Hz, 4H), 4.84 (t, J = 7.2 Hz, 2H), 4.01 (t, J = 6.4 Hz, 4H), 2.20-2.16 (m, 2H), 1.88-1.84 (m, 4H), 1.57-1.52 (m, 4H), 1.45-1.36 (m, 14H), 0.99-0.92 (m, 9H).

13

C NMR

(CDCl3, 100 MHz): δ 191.9, 155.9, 148.7, 143.4, 142.7, 142.5, 140.5, 135.6, 132.2, 132.1, 130.2, 129.9, 129.8, 129.0, 127.3, 127.2, 127.1, 125.7, 125.4, 124.5, 119.0, 115.5, 68.3, 57.6, 31.7, 31.2, 30.3, 29.4, 26.3, 25.8, 22.7, 22.5, 14.2, 14.0. MS (FAB) m/z : 800.2 (M+). FAB-HRMS calcd for C53H60N4O3: 800.4662, Found: 800.4637.

Synthesis of NTD-1. To a flask containing a mixture of 3a (0.15 g, 0.28 mmol), cyanoacetic acid (0.031g, 0.36 mmol) and ammonium acetate (7 mg, 0.008 mmol) was added acetic acid (10 mL). The mixture was heated at 100 ºC for 8 h, and allowed to cool to room temperature. After cooling, it was poured into water and extracted with CH2Cl2. The organic extracts were washed with brine solution and dried over anhydrous MgSO4. Further purification by silica gel chromatography using dichloromethane/acetic acid as the eluent afforded the desired product as dark purple powder in 77% yield. 1H NMR (d6-acetone, 400 MHz): δ 8.63 (s, 1H), 8.31 (d, J = 8.8 Hz, 1H), 8.24 (d, J = 4.0 Hz, 1H), 8.21 (d, J = 8.8 Hz, 1H), 7.55 (d, J = 4.0 Hz, 1H), 7.59 (t, J = 8.0 Hz, 1H), 7.54 (d, J = 8.0 Hz, 2H), 7.51 (t, J = 8.0 Hz ,1H), 7.23 (d, J = 8.0 Hz, 4H), 7.06 (d, J = 8.0 Hz, 2H), 6.99 (d, J = 8.0 Hz, 4H), 4.02 (t, J = 6.8 Hz, 4H), 1.83-1.76 (m, 4H), 1.52-1.47 (m, 4H), 1.39-1.35 (m, 8H), 0.91 (t, J = 7.2 Hz). 13C NMR (d8-THF, 100 MHz): δ 157.4, 152.6, 150.3, 147.7, 146.8, 141.4, 139.1, 138.2, 134.2, 133.9, 133.3, 132.7, 128.7, 128.3, 128.2, 127.1, 127.0, 120.9, 119.5, 116.7, 116.3, 101.1, 69.0, 32.8, 30.5, 26.9, 23.7, 14.5. MS (FAB) m/z: 806.2 (M+). Anal. Calcd for C48H46N4O4S2: C, 71.44; H, 5.75; N, 6.94. Found: C, 71.16; H, 5.69; N, 6.73.


9


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 10 of 38

Synthesis of NTD-2. The synthetic method was similar to that of NTD-1 and the crude product was purified with column chromatography on silica gel using dichloromethane/acetic acid as the eluent afforded the desired product as red powder in 72% yield. 1H NMR (d6-acetone, 400 MHz): δ 8.53 (s, 1H), 8.38 (d, J = 8.0 Hz, 2H), 8.19 (d, J = 8.0 Hz, 1H), 8.00 (d, J = 8.0 Hz, 1H), 7.94 (d, J = 8.0 Hz, 2H), 7.53 (d, J =8.0 Hz, 2H), 7.50-7.47 (m, 1H), 7.22 (d, J =8.0 Hz, 4H), 7.07 (d, J = 8.0 Hz, 2H), 6.99 (d, J = 8.0Hz, 4H), 4.02 (t, J = 6.8 Hz, 4H), 1.81-1.76 (m, 4H), 1.52-1.48 (m, 4H), 1.39-1.34 (m, 8H), 0.90 (t, J = 6.4 Hz, 6H). 13C NMR (d6-acetone, 400 MHz): δ 164.3, 157.7, 155.6, 152.9, 150.6, 143.3, 141.7, 133.9, 133.8, 133.3, 133.0, 132.3, 129.1, 128.8, 128.7, 128.6, 127.7, 119.9, 117.1, 117.0, 105.3, 69.45, 32.9, 29.9, 27.1, 23.9, 14.9. MS (FAB) m/z: 800.2 (M+). Anal. Calcd for C50H48N4O4S: C, 74.97; H, 6.04; N, 6.99. Found: C, 74.74; H, 6.01; N, 7.03. Synthesis of NTD-3. The synthetic method was similar to that of NTD-1 and the crude product was purified with column chromatography on silica gel using dichloromethane/acetic acid as the eluent afforded the desired product as dark red powder in 81% yield. 1H NMR (d8THF, 500 MHz): δ 8.53 (s, 1H), 8.32 (d, J = 10.0 Hz, 1H), 8.19 (d, J = 10.0 Hz, 1H), 8.12 (d, J = 5.0 Hz, 1H), 7.65 (d, J = 5.0 Hz, 1H), 7.54 (d, J = 5.0 Hz, 2H), 7.51-7.48 (m, 1H), 7.44-7.41 (m, 1H), 7.33-7.30 (m, 4H), 7.25-7.23 (m, 6H),7.08-7.05 (m, 2H). 13C NMR (d8-THF, 125 MHz): δ 164.1, 152.5, 149.3, 148.8, 147.5, 146.7, 139.2, 138.1, 133.9, 133.7, 133.5, 132.7, 130.7, 130.4, 128.7, 128.5, 127.3, 127.2, 126.1, 124.4, 123.1, 121.4, 116.7, 101.2. MS (FAB) m/z: 606.2 (M+). Anal. Calcd for C36H22N4O2S2: C, 71.27; H, 3.66; N, 9.23. Found: C, 71.05; H, 3.58; N, 9.17. Synthesis of NTz-1. The synthetic method was similar to that of NTD-1 and the crude product was purified with column chromatography on silica gel using dichloromethane/acetic acid as the eluent afforded the desired product as dark red powder in 86% yield. 1H NMR (d8-THF, 400


10

Page 11 of 38

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


MHz): δ 8.52 (s, 1H), 8.41 (d, J = 8.8 Hz, 1H), 8.22 (d, J = 8.8 Hz, 1H), 8.12 (d, J = 4.0 Hz, 1H), 7.72 (d, J = 4.0 Hz, 1H), 7.50 (d, J = 8.8 Hz, 2H), 7.44 (t, J = 8.4 Hz, 1H), 7.32 (d, J = 8.4 Hz, 1H), 7.17 (d, J = 8.8 Hz, 4H), 7.03 (d, J = 8.8 Hz, 2H), 6.89 (d, J = 8.8 Hz, 4H), 4.84 (t, J = 6.4 Hz, 2H), 3.95 (t, J = 6.4 Hz, 4H), 2.17-2.10 (m, 2H), 1.81-1.76 (m, 4H), 1.54-1.30 (m, 18H), 0.96-0.95 (m, 9H).

13

C NMR (d8-THF, 100 MHz): δ 157.4, 150.1, 148.3, 143.8, 143.6, 141.5,

138.5, 138.1, 133.0, 132.1, 131.9, 131.7, 131.0, 128.3, 128.1, 128.0, 127.1, 126.4, 125.4, 119.6, 117.7, 116.8, 116.3, 100.6, 69.0, 32.7, 32.3, 31.1, 30.5, 27.3, 26.9, 23.7, 23.5, 14.5, 14.4, 14.1. FAB-HRMS calcd for C54H59N5O4S: 873.4282, found 873.4253. Anal. Calcd for C54H59N5O4S: C, 74.20; H, 6.80; N, 8.01. Found: C, 74.25; H, 6.82; N, 8.09. Synthesis of NTz-2. The synthetic method was similar to that of NTD-1 and the crude product was purified with column chromatography on silica gel using dichloromethane/acetic acid as the eluent afforded the desired product as dark red powder in 81% yield. 1H NMR (d6-acetone, 400 MHz): δ 8.46 (s, 1H), 8.30 (d, J = 8.8 Hz, 2H), 8.15 (d, J = 8.4 Hz, 1H), 8.01 (d, J = 8.4 Hz, 1H), 7.88 (d, J = 8.4 Hz, 2H), 7.45 (d, J = 8.4 Hz, 2H), 7.36-7.28 (m, 2H), 7.12 (t, J = 8.8 Hz, 4H), 6.98 (d, J = 8.8 Hz, 2H), 6.89 (d, J = 8.8 Hz, 4H), 4.74 (t, J = 7.2 Hz, 2H), 3.94 (t, J = 6.4 Hz, 4H), 2.07-2.04 (m, 2H),1.75-1.72 (m, 4H), 1.47-1.25 (m, 18H), 0.90-0.79 (m, 9H). 13C NMR (d6acetone, 100 MHz): δ 164.1, 157.3, 155.2, 149.9, 143.7, 143.6, 142.0, 141.5, 133.5, 133.2, 132.3, 132.0, 131.1, 130.9, 129.9, 128.5, 128.4, 127.9, 126.7, 126.6, 125.7, 125.6, 119.8, 117.0, 116.6, 104.7, 69.1, 58.4, 32.6, 32.1, 31.1, 30.7, 29.6, 27.2, 26.8, 23.6, 23.4, 14.6, 14.5. FAB-HRMS calcd for C56H61N5O4: 867.4721, found 867.4688. Anal. Calcd for C56H61N5O4: C, 77.48; H, 7.08; N, 8.07. Found: C, 77.35; H, 6.99; N, 7.96. Assembly and characterization of DSSCs: The photoanode used was the TiO2 thin film (12 µm of 20 nm particles as the absorbing layer and 6 µm of 400 nm particles as the scattering


11


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 12 of 38

layer) coated on fluorine-doped tin oxide (FTO, 15Ω/square) glass substrate with a dimension of 0.5 × 0.5 cm2. The film thickness was measured by a profilometer (Dektak3, Veeco/Sloan Instruments Inc., USA). A platinized FTO produced by thermopyrolysis of H2PtCl6 was used as the counter electrode. The TiO2 thin film was dipped into the THF solution containing 3×10-4 M of dye sensitizers for at least 12 h. After rinsing with CH3CN, the photoanode adhered with a polyester tape of 30 µm in thickness and with a square aperture of 0.36 cm2 was placed on the top of the counter electrode and the two were tightly clipped them together to form a cell. Electrolyte was then injected into the void space of the cell, which was then sealed with the Torr Seal® cement (Varian, MA, USA). The electrolyte was composed of 0.5 M lithium iodide (LiI), 0.05 M iodine (I2), and 0.5 M 4-tert-butylpyridine dissolved in acetonitrile. The photoelectrochemical characterizations on the solar cells were carried out using an Oriel Class AAA solar simulator (Oriel 94043 A, Newport Corp.). Photocurrent-voltage characteristics of the DSSCs were recorded with a potentiostat/galvanostat (CHI650B, CH Instruments, Inc.) at a light intensity of 100 mWcm-2 calibrated by an Oriel reference solar cell (Oriel 91150, Newport Corp.). The monochromatic quantum efficiency was recorded through a monochromator (Oriel 74100, Newport Corp.) at short circuit condition. The intensity of each wavelength was in the range of 1 to 3 mWcm-2. Electrochemical impedance spectra (EIS) were recorded for DSSCs in the dark at -0.65 V potential at room temperature, whose frequency travelled ranged from 10 mHz to 100 kHz.

Quantum chemistry computation. Q-Chem 4.0 software was used for the computation.45 Geometry optimization of the molecules were performed using hybrid B3LYP functional and 631G* basis set. A number of possible conformations were examined for each molecule and the


12

Page 13 of 38

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


one with the lowest energy was used. The same functional was also applied for the calculation of excited states using time-dependent density functional theory (TD–DFT). TD–DFT was employed to characterize excited states with charge-transfer character in a number of previous works,46 and underestimation of the excitation energies was seen in some cases.47 Therefore, here we use TD–DFT to visualize the extent of transition moments as well as their charge-transfer characters, and avoid drawing conclusions from the excitation energy.

RESULTS AND DISCUSSION Synthesis of the Materials. The new dyes synthesized, NTD-1 to NTD-3 and NTz-1 to NTz2, are shown in Figure 1. The synthetic pathways are illustrated in Scheme 1. The compound 1a was obtained from the reaction of N-thionylaniline, trimethylsilyl chloride and 1,4-dibromo-2,3diaminonaphthalene. After filtration, the precipitate was recrystallized from a mixture of ethanol and chloroform to afford 1a in 70%. The compound 1b was synthesized in two steps by following a modified reported method:48-50 (1) reaction of 1,4-dibromo-2,3-diaminonaphthalene with sodium nitrite under acidic conditions to give non-alkylated NTz intermediate; (2) subsequent alkylation of the NTz intermediate in DMF using triethylamine as the base. Stille coupling reaction51 between 1a or 1b and triarylamine stannyl derivatives afforded intermediates 2a−2c. These intermediates underwent the second Stille coupling with appropriate organotin compounds containing a protected formyl group, and subsequent deprotection reaction provided the desired aldehydes, 3a−3d. The aldehydes were then converted to the final products, NTD-1 to NTD-3 and NTz-1 to NTz-2, via Knoevenagel reaction with 2-cyanoacetic acid in the presence of ammonium acetate in acetic acid. >


13


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 14 of 38

> Optical Properties. The electronic absorption spectra of the dyes in THF solution are shown in Figure 2, and the relevant data are presented in Table 1. The bands below 400 nm can be attributed to localized π−π* transition, while the band between 400−700 nm is the intramolecular charge transfer transition (ICT) from the arylamine donor to the 2-cyano acrylic acid acceptor with more delocalized π−π* transition character. The ICT absorption maximum for NTD-1, NTD-2 and NTD-3 is at 544, 532 and 522 nm, respectively. The longer absorption wavelength of NTD-1 than NTD-2 can be ascribed to the higher tendency of the thiophene than benzene to from quinoid structure which is beneficial for electronic resonance.52-54 The shorter absorption wavelength of NTD-3 than NTD-1 can be attributed to the enhanced electron-donating ability of the arylamine in the latter due to incorporation of the alkoxy chain.20,25 The absorption wavelength of the compound NTD-1 is longer than its congener S124 (491 nm) and R125 (466 nm), indicating that the naphtho[2,3-c][1,2,5]thiadiazole unit indeed more effectively red shifts the absorption compared with the benzo[2,1,3]thiadiazole entity. > > The absorption maxima at low energy transition of NTz-1 and NTz-2 appeared at 464 and 454 nm, respectively. From BT25,26 to BTz,33,36 or from pyridal[2,1,3]thiadiazole (PyT)38 to 2H[1,2,3]triazolo[4,5-c]pyridine (PT),39 the ICT band is blue shifted by > 60 nm for the molecules with the triazole entity. Compared with NTD-based dyes, blue shift (~80 nm) of the ICT band in NTz-1 and NTz-2 can therefore be attributed to the greater electron-accepting ability of the sulfur than the nitrogen atom. The higher molar extinction coefficient of NTz-1 (or NTz-2)


14

Page 15 of 38

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


compared to NTD-based dyes is due to the slightly better molecular planarity (vide infra) and the stronger π–π* transition character in the former (vide infra). The absorption spectra of the dyes adsorbed on TiO2 film with and without the coabsorbent CDCA are shown in Figure S2. The absorption spectra of NTD-based dyes are significantly broadened and red shifted compared with the solution spectra, indicating existence of Jaggregation of the dyes on the TiO2 surface. There is much less dye aggregation for NTz-1 and NTz-2 dyes, indicating that the hexyl substituent at the nitrogen atom of the triazole entity helps with suppression of dye aggregation. The least aggregation of NTz-2 can be partially attributed to the large twist angles between the NTz entity and the two neighboring phenyl rings (vide infra). Narrower absorption with cutoff at shorter wavelength (Figure S2) suggests that dye aggregation has been significantly alleviated after addition of CDCA. Electrochemical Properties. The electrochemical properties of the dyes were investigated by cyclic voltammery (CV), and the data are summarized in Table 1. Representative cyclic voltammograms of the dyes are shown in Figure S3. Except for NTD-3, all the dyes exhibit a quasi-reversible one-electron oxidation couple which can be attributed to the oxidation of the arylamine. The oxidation potential of dye NTD-3 (1.29 V) is higher than that of NTD-1 (1.01 V) due to the presence of a better electron donor, 4-(bis(4-hexoxyphenyl)aminophenyl, in the latter. The oxidation potentials of NTD-1 and NTD-2 dyes are almost equal to that of NTz dyes, indicating that the four dyes have similar HOMO levels. On the contrary, the LUMO energy of NTz-based dyes is higher than that of NTD-based dyes due to the more electron-deficient nature of the NTD entity. The excited state potential (E0-0*) of the sensitizer was estimated from the first oxidation potential (Eox) at the ground state and the zero-zero excitation energy (E0-0) estimated from the absorption onset. The deduced E0-0* values (-0.66 to -1.26 V vs. NHE, see


15


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 16 of 38

Table 1) are more negative than the conduction-band-edge energy level of the TiO2 electrode (0.5 V vs. NHE)55 and the first oxidation potentials of the dyes (1.01 to 1.29 V vs. NHE) are more positive than the I-/I3- redox couple (~0.4 V vs. NHE).56 These results assure favorable electron injection upon photo-excitation and regeneration of the dye after electron injection. Photovoltaic Devices. DSSCs with an effective area of 0.25 cm2 were fabricated using the new dyes as the sensitizers, and nanocrystalline anatase TiO2 as the photoanode. The electrolyte was composed of 0.8 M PMII/0.05 M I2/0.10 M LiI/0.5 M tert-butylpyridine in acetonitrile solution. The performance parameters of the DSSCs under AM 1.5 illumination are listed in Table 2. The incident photon-to-current conversion efficiency (IPCE) plots of the cells are shown in Figure 3, and the photocurrent-voltage (J-V) curves under illumination and in the dark are shown in Figure 4. DSSCs based on NTD-1 and NTD-3 dyes have only low performance: NTD1, JSC = 4.51 mA cm−2, VOC = 574 mV, FF = 0.76, η = 1.94%; NTD-3, JSC = 2.84 mA cm−2, VOC = 546 mV, FF = 0.76, η = 1.17%. In comparison, the device based on NTD-2 has a short-circuit photocurrent density (JSC) of 12.71 mA cm-2, an open-circuit voltage (VOC) of 0.677 V, and a fill factor (FF) of 0.74, corresponding to an overall conversion efficiency (η) of 6.37% which was ~79% of the standard cell based on ruthenium dye N719 (8.02%). Though NTD-2 has the lowest light harvesting efficiency in the solution among three NTD dyes, it has much higher PCE than the other two in the range of 400–650 nm. Less planar skeleton of NTD-2 obviously can more effectively suppress dark current (Figure 4), leading to a higher VOC. Aggregation induced excited state quenching may be also eased due to less planar conformation of NTD-2, resulting in more efficient electron injection. An interesting feature of the NTD dyes is that J-aggregation of the dyes has important contribution to light harvesting/electron injection at the longer wavelength region extending beyond 700 nm, as evidenced from the IPCE spectra.


16

Page 17 of 38

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


Compared with the NTD dyes, the IPCE spectra of NTz-1 (700 nm) and NTz-2 (650 nm) have cutoff at slightly shorter wavelength. However, the maximum PCE values are significantly higher than those of the NTD dyes and reach ~75% at 460 and 450 nm for NTz-1 and NTz-2, respectively. Accordingly, these two dyes show relatively large photocurrents: NTz-1, 14.73 mA cm−2; NTz-2, 13.13 mA cm−2. Less dye aggregation (vide supra) of NTz dyes than NTD dyes is believed to be an important factor to the higher PCE value of the former due do less excited state quenching. The adsorbed dye densities of the sensitizers on TiO2 were measured to be 2.60 × 107

, 3.66 × 10-7, 3.22 × 10-7, 5.10 × 10-7 and 3.20 × 10-7 mol/cm2, for NTD-1, NTD-2, NTD-3,

NTz-1 and NTz-2, respectively. Therefore, higher dye loading of NTz-1 may also contribute to the higher photocurrent. The higher cell efficiency of NTz- than NTD-based dyes can be rationalized by the following reasons: (1) the NTz dyes have significantly higher absorption intensity at below 500 nm; (2) the NTz dyes have less dye aggregation (Figure S2) which facilitates electron injection; (3) NTz dyes have smaller dark current than NTD dyes because of more effective dark current suppression of the former (vide infra); (4) NTz dyes have smaller degree of negative charge collection (i.e., charge trapping) and therefore better electron injection based on Mulliken charge analysis for the S0 → S1 transition (vide infra). > > > The higher cell open-circuit voltage of NTz dyes than NTD dyes is in accordance with the smaller dark current in the former. The higher cell voltage of NTD-2 (or NTz-2) than NTD-1 (or NTz-1) is consistent with the smaller dark current of the former (Figure 4). The larger twist angle (vide infra, see computation section) between the NTD or NTz unit and the phenyl ring


17


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 38

apparently leads to more effective suppression of the dark current in the cells of NTD-2 and NTz-2. Similar phenomenon was also found in the benzene and thiophene congeners of BTbased sensitizers.27 Thiophene ring was reported to be able to interact with I2 (or I3−) and resulted in lower VOC values in DSSCs.36 Therefore, the possibility of thiophene ring in NTD-1 and NTz1 contributing to lower VOC cannot be completely ruled out. Significantly lower dark current observed for NTz-2 is in conformity with the electrochemical impedance studies in the dark (vide infra). Aggregation of the dye molecules frequently jeopardizes their electron injection efficiencies. In order to disrupt unfavorable dye aggregation on TiO2 and improve electron injection, a frequently used anti-aggregation co-adsorbent, CDCA,57-60 was added in different concentrations (30 mM for NTD-1 to NTD-3; 5 mM for NTz-1 to NTz-2) during dye soaking of the sensitizers. The photovoltaic parameters of the cells with CDCA adsorbent are listed in Table 2. Both JSC and VOC values increased for the cells of NTD-1 to NTD-3 at 30 mM of CDCA, suggesting effective alleviation of dye aggregation with added CDCA. For NTD-2, the power conversion efficiency (η) of was significantly improved to 7.53%, reaching ~94% of a N719-based DSSC (8.02%) fabricated and measured under the same conditions. As there is much less dye aggregation of NTz than NTD dyes, adding even 5 mM of CDCA as the co-adsorbent results in decrement of the JSC value in DSSCs based on NTz dyes. Obviously the current gain due to antiaggregation of the dye cannot compensate for the loss of light harvesting at the longer wavelengths benefited from dye aggregation and decreased dye loading due to competition of CDCA for the adsorption sites. In contrast to the photocurrent, there is increment in the VOC value in the cells of NTz dyes upon adding CDCA. Evidently CDCA helps with blocking the TiO2 surface, preventing recombination of the TiO2 electrons with the oxidized electrolytes.


18

Page 19 of 38

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


Electrochemical impedance spectroscopy analysis. The electrochemical impedance spectra (EIS) of DSSCs were obtained under a forward bias of -0.65 V in the dark, and the Nyquist plots for DSSCs based on NTD-1, NTD-2, NTD-3, NTz-1 and NTz-2 are shown in Figure 5a. The Bode phase plots are also shown in Figure 5b. The large semicircle in the Nyquist plots was used to derive the charge recombination resistance on the TiO2 surface (Rrec) by fitting curves using Zview software. The cell of NTD-2 exhibits a larger resistance value that of NTD-1 or NTD-3, which is consistent with its smaller dark current (Figure 4). The cell of NTz-1 (or NTz-2) exhibits a much larger resistance value than that of NTD-1 (or NTD-2), which is in parallel with its smaller dark current and larger VOC measured (vide supra). Similar to many literature reports,28,61-62 the alkyl chains at 2-position of NTz unit appears to be beneficial to dark current suppression in the cell of NTz-1 and NTz-2. In the Bode phase plots, the peak with the frequency lying in the range of 1−102 Hz represents the electron transfer frequency at the TiO2/dye/electrolyte interface. The charge recombination (recapture of the conduction band electrons by I3–) lifetime therefore increases in the order of NTD-3 < NTD-1 < NTD-2 < NTz-1 < NTz-2 (Figure 5b), which is in the same trend with the recombination resistance. > > Theoretical Approach. Theoretical computations were carried out on these molecules by density functional theory (DFT) and time-dependent DFT in order to gain insight of molecular structure vs. solar cell performance. The results for theoretical computation are included in Table S1 (see the Supporting Information). Figure S4 shows the ground-state geometries of the dyes with the dihedral angles between two neighboring conjugated segments indicated. The molecules were divided into several segments: the arylamine group (Am), the phenyl group (Ph), the


19


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 20 of 38

thiophene unit (T: the unit between NTD or NTz and Ac), and 2-cyano-acrylic acid (Ac). The twist angle between the NTD (or NTz) entity and its neighboring aromatic entity is expected to be larger than that between the benzothiadiazole (or benzotriazole) entity, due to the larger dimension of the former. However, the more electron deficient nature of NTD and NTz still leads to red shift of the ICT band in the D–A–π–A congeners. For example, in spite of the larger dihedral angle (53.4o) between naphtho[2,3-c][1,2,5]thiadiazole entity and the neighboring phenyl ring than that (34.0o) between the benzo[2,1,3]thiadiazole entity and the neighboring phenyl ring (S1), the ICT absorption maximum of NTD-3 is larger than that of S1 by 22 nm. The frontier orbitals of the dyes are shown in Figure S5. The HOMO of these dyes is mainly contributed by the triarylamine, though with extension to nearly the whole molecule except the carboxylic acid anchor. On the contrary, the LUMO is mainly composed of the anchor and the conjugated spacer except diarylamine. However, there exists slight difference between the NTD and NTz dyes: the NTD entity has more contribution to the LUMO than the NTz entity, and NTz entity has more contribution to the HOMO than NTD. The S0 → S1 transition is nearly HOMO → LUMO transition. Therefore, the lowest energy absorption has charge transfer character for these dyes. The Mulliken charge shifts for the S1 and S2 states were also calculated from the TDDFT results. Differences in the Mulliken charges in the excited and ground states were grouped into several segments in the molecules to estimate the extent of charge separation upon excitation (Figure S6). The NTD entity has significantly higher negative charge than the 2cyano acrylic acid in the S1 and S2 states for NTD-based dyes. In comparison, the negative charge at the NTz entity is comparable or smaller than that of the 2-cyano acrylic acid for the S1 and S2 states. Based on our previous observation on the sensitizers constructed from BT24 vs. BTz36 and pyridal[2,1,3]thiadiazole (PyT)38 vs. 2H-[1,2,3]triazolo[4,5-c]pyridine (PT),39 more


20

Page 21 of 38

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


negative Mulliken charge at the NTD entity may be detrimental to the electron injection and consequently lowers the cell performance.

CONCLUSIONS In

summary,

we

have

synthesized

new

organic

dyes

containing

naphtho[2,3-

c][1,2,5]thiadiazole (NTD) and naphtho[2,3-d][1,2,5]triazole (NTz) in the conjugated spacer between the arylamine donor and 2-cyanoacrylic acceptor as the sensitizers for dye-sensitized solar cells. With a stronger electron-accepting NTD unit, NTD-based dyes have more red shifted absorption. However, dye aggregation and charge trapping at the NTD entity lead to less efficient electron injection of the NTD dyes. Though the efficiency of the best performance cell based on NTD-2 (η = 6.37%, JSC = 12.71 mA cm-2, VOC = 0.677 V, FF = 0.74) reaches only ~79% of the standard cell based on N719, anti-aggregation of the dyes by adding CDCA coadsorbent helps to improve the cell efficiency up to 7.53%, which is 94% of the standard cell. Replacement of the naphtho[2,3-c][1,2,5]thiadiazole entity by naphtho[2,3-c][1,2,5]triazole entity significantly alleviates charge trapping and dye aggregation, and suppresses the dark current. Because of less charge trapping of the NTz entity, less dye aggregation and more efficient dark current suppression, NTz dyes have higher cell performance than NTD dyes. The best cell performance of NTz-1 has a conversion efficiency of 7.23% without CDCA coadsorbent, reaching ∼90% of the standard cell based on N719.


21


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 22 of 38

Figure 1. The structure of the dyes. Scheme 1. Synthesis routes for NTD-1~3 and NTz-1~2 dyes. R

R N

SnBu3

N

PhNSO, TMSCl H2N Br

N

NH2

X

X

O

N

1. Bu3Sn Ar O

N

N

Br

PdCl2(PPh3)2

R Br

Br

DMF

Br

1. NaNO2 HOAc

PdCl2(PPh3)2

2. 1-hexylBr NEt3, DMF

2. HOAc/H2O

R

DMF

2a-c 2a: R = OHex; X = S

1a; X = S 1b; X = N(C6H13)

2b: R = H; X = S 2c: R = OHex; X = N(C6H13)

R N

X

R N

N

O N

NC

Ar

X

N

NC COOH

COOH N

H

Ar

NH4OAc HOAc R

R 3a-d

3a: R = OHex; X = S; Ar =

S

NTD-1: R = OHex; X = S; Ar =

S

NTD-2: R = OHex; X = S; Ar = 3b: R = OHex; X = S; Ar = 3c: R = H; X = S; Ar =

NTD-3: R = H; X = S; Ar =

S

3d: R = OHex; X = N(C6H13); Ar =

S

S

NTz-1: R = OHex; X = N(C6H13); Ar =

S

NTz-2: R = OHex; X = N(C6H13); Ar = 3e: R = OHex; X = N(C6H13); Ar =


22

-1

45000 40000

-1

NTD1 NTD2 NTD3 NTz-1 NTz-2

35000 30000 25000 20000 15000 10000 5000 0 300

400

500

600

700

800

Wavelength (nm)

Figure 2. The absorption spectra of the dyes in THF.

100

NTD-1 NTD-1+30mM CDCA NTD-2 NTD-2+30mM CDCA NTD-3 NTD-3+30mM CDCA NTZ-1 NTZ-1+5mM CDCA NTZ-2 NTZ-2+5mM CDCA

80

IPCE (%)

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


Molar extinction Coefficient (M cm )

Page 23 of 38

60 40 20 0 400

500

600

700

800

Wavelength (nm) Figure 3. IPCE plots of the DSSCs using the dyes.


23

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

Photocurrent density (mA/cm2)


Page 24 of 38


15 10 5 0 -5 0.0

0.2

0.4

0.6

0.8

Photovoltage (V) Figure 4. J-V curves of DSSCs based on the dyes.

Table 1. Electrooptical Parameters of the Dyesa. Eoxc V

E0-0d eV

E0-0*e V

313 (118)

1.01

1.88

-0.87

532 (0.95)

308 (117)

1.01

1.97

-0.96

NTD-3

522 (1.44)

588 (NA)

1.29

1.95

-0.66

NTz-1

464 (2.64)

306 (112)

1.01

2.17

-1.16

NTz-2

454 (2.43)

309 (359)

1.01

2.27

-1.26

S1

491 (2.75), 388 (1.63), 309 (2.84)

581 (91)

1.28

2.12

-0.84

R1

466 (2.01), 408 (1.37), 307 (2.26)

606 (169)

1.31

2.29

-0.98

dye

λabs (ε × 104 M-1 cm-1) a nm

E1/2 (ox) mV

NTD-1

544 (1.05)

NTD-2

b

a

The absorption spectra were recorded in THF. bThe cyclic voltammetric studies were conducted in THF. Scan rate: 100 mV/sec, Electrolyte: (n-C4H9)4NPF6; ∆Ep is the separation


24

Page 25 of 38

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


between the anodic and cathodic peaks and in unit of mV. Potentials are quoted with reference to the internal ferrocene standard (E1/2 = +265 mV vs Ag/AgNO3). cEox: The oxidation potential vs. NHE, EFc = 0.7 V vs. NHE. dE0-0 was determinated from the absorption onset. eE0-0*: The excited state oxidation potential vs. NHE.

Table 2. Performance Parameters of DSSCs Constructed Using the Dyesa.

Dye

CDCA (mM)

JSC (mA/cm2)

VOC (V)

FF

η (%)

NTD-1

0

4.35±0.15

0.574±0.003

0.76±0.01

1.94±0.05

30

8.97±0.11

0.585±0.001

0.73±0.01

3.83±0.03

0

12.71±0.25

0.677±0.002

0.74±0.01

6.37±0.14

30

15.09±0.06

0.689±0.003

0.72±0.01

7.53±0.08

0

2.84±0.17

0.546±0.004

0.76±0.01

1.17±0.07

30

3.29±0.11

0.573±0.001

0.77±0.01

1.45±0.08

0

14.73±0.05

0.707±0.005

0.69±0.01

7.23±0.17

5

13.73±0.12

0.739±0.002

0.74±0.01

7.48±0.08

0

13.13±0.11

0.741±0.003

0.73±0.01

7.09±0.10

5

12.06±0.11

0.752±0.004

0.72±0.01

6.57±0.05

S1b

13.5

0.58

0.64

5.01

R1b

12.0

0.68

0.68

5.57

N719

15.12±0.18

0.746±0.006

0.71±0.01

8.02±0.06

NTD-2

NTD-3

NTz-1

NTz-2

a

Based on five measurements. bref. 25.


25

300

10

250

Z" (ohm) 0

200

20

Page 26 of 38


Z' (ohm) 40

150 100 50 0 0

100

200

300

400

500

Z' (ohm)

(a)


60

Phase (deg)

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

Z" (ohm)


50 40 30 20 10 0 -1

10

(b)

0

10

1

10

2

10

3

10

4

10

5

10

Frequency (Hz)

Figure 5. Electrochemical impedance spectra (a) Nyquist plots (b) Bode plots of DSSCs measured in the dark under –0.65 V bias.


26

Page 27 of 38

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


ASSOCIATED CONTENT Supporting Information. Frontier orbitals of relevant monomers (Figure S1), absorption spectra with and without CDCA coadsorbent on TiO2 films (Figure S2), cyclic voltammogram (Figure S3) and dihedral angles (Figure S4), frontier orbitals (Figure S5), the difference in the Mulliken charges (Figure S6) and calculated low-lying transition (Table S1) data, 1H NMR and 13C NMR spectra of NTD-1~3 and NTz-1~2 (Figure S7~S16). This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT Financial support of this research by Academia Sinica (AS) and Ministry of Science and Technology (MOST, Taiwan) are gratefully acknowledged. Support from the Instrumental Center of Institute of Chemistry (AS) is also acknowledged.


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

Page 28 of 38

REFERENCES (1) O’Reagen, B.; Grätzel, M. A Low-Cost, High-Efficiency Solar Cell based on Dye-Sensitized Colloidal TiO2 films. Nature 1991, 353, 737–740. (2) Chiba, Y.; Islam, A.; Watanabe, Y.; Komiya, R.; Koide, N.; Han, L. Dye-Sensitized Solar Cells with Conversion Efficiency of 11.1%. Jpn. J. Appl. Phys. 2006, 45, L638–L640.

(3) Gao, F.; Wang, Y.; Shi, D.; Zhang, J.; Wang, M.; Jing, X.;Humphry-Baker, R.; Wang, P.; Zakeeruddin, S. M.; Grätzel, M. Enhance the Optical Absorptivity of Nanocrystalline TiO2 Film with High Molar Extinction Coefficient Ruthenium Sensitizers for High Performance Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2008, 130, 10720–10728. (4) Decoppet, J.-D.; Tsai, J.-H.; Grätzel, 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. (5) Cao, Y.; Bai, Y.; Yu, Q.; Cheng, Y.; liu, S.; Shi, D.; Gao, 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. (6) Sauvage, F.; Decoppet, J.-D.; Zhang, M.; Zakeeruddin, S. M.; Comte, P.; Nazeeruddin, M.; Wang, P.; Grätzel, M. Effect of Sensitizer Adsorption Temperature on the Performance of Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2011, 133, 9304–9309. (7) Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Dye-Sensitized Solar Cells


28

Page 29 of 38

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


with 13% Efficiency Achieved Through the Molecular Engineering of Porphyrin Sensitizers. Nat. Chem. 2014, 6, 242–247. (8) Lee, K.-M.; Hsu, Y.-C.; Ikegamic, M.; Miyasaka, T.; Justin Thomas, K. R.; Lin, J. T.; Ho, K.-C. Co-sensitization Promoted Light Harvesting for Plastic Dye-Sensitized Solar Cells. J. Power Sources 2011, 196, 2416–2421. (9) Fan, S.-Q; Kim, C.; Fang, B.; Liao, K.-X.; Yang, G.-J.; Li, C.-J.; Kim, J.-J.; Ko, J. Improved Efficiency of over 10% in Dye-Sensitized Solar Cells with a Ruthenium Complex and an Organic Dye Heterogeneously Positioning on a Single TiO2 Electrode. J. Phys. Chem. C 2011, 115, 7747–7754. (10)

Han, L.; Islam, A.; Chen, H.; Malapaka, C.; Chiranjeevi, B.; Zhang, S.; Yang, X.;

Yanagida, M. High-Efficiency Dye-Sensitized Solar Cell with a Novel Co-adsorbent. Energy Environ. Sci. 2012, 5, 6057–6060. (11)

Pei, K.; Wu, Y. Z.; Li, H.; Geng, Z. Y.; Tian, H.; Zhu, W. H. Cosensitization of D-A-π-A

Quinoxaline Organic Dye: Efficiently Filling the Absorption Valley with High Photovoltaic Efficiency. ACS Appl. Mater. Interfaces 2015, 7, 5296–5304. (12)

Robertson, N. Optimizing Dyes for Dye-Sensitized Solar Cells. Angew. Chem. Int. Ed.

2006, 45, 2338–2345 (13)

Robertson, N. Catching the Rainbow: Light Harvesting in Dye-Sensitized Solar Cells.

Angew. Chem. Int. Ed. 2008, 47, 1012–1014.


29


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

(14)

Page 30 of 38

Ning, Z.; Tian, H. Triarylamine: A Promising Core Unit for Efficient Photovoltaic

Materials. Chem. Commun. 2009, 5483–5495. (15)

Ooyama, Y.; Harima, Y. Molecular Designs and Syntheses of Organic Dyes for Dye-

Sensitized Solar Cells. Eur. J. Org. Chem. 2009, 2903–2934. (16)

Mishra, A.; Fischer, M. K. R.; Bäuerle, P. Metal-Free Organic Dyes for Dye-Sensitized

Solar Cells: From Structure: Property Relationships to Design Rules. Angew. Chem. Int. Ed. 2009, 48, 2474–2499. (17)

Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Dye-Sensitized Solar Cells.

Chem. Rev. 2010, 110, 6595–6663. (18)

Bessho, T.; Zakeeruddin, S. M.; Yeh, C.-Y.; Diau, E. W.-G.; Grätzel, M. Highly Efficient

Mesoscopic Dye‐Sensitized Solar Cells Based on Donor–Acceptor‐Substituted Porphyrins. Angew. Chem. Int. Ed. 2010, 49, 6646–6649. (19)

Yen, Y.-S.; Chou, H.-H.; Chen, Y.-C.; Hsu, C.-Y.; Lin, J. T. Recent Developments in

Molecule-Based Organic Materials for Dye-Sensitized Solar Cells. J. Mater. Chem. 2012, 22, 8734–8747. (20)

Zheng, W.; Cao, Y.; Bai, Y.; Wang, Y.; Shi, Y.; Zhang, M.; Wang, F.; Pan, C.; Wang, P.

Efficient Dye-Sensitized Solar Cells with an Organic Photosensitizer Featuring Orderly Conjugated Ethylenedioxythiophene and Dithienosilole Blocks. Chem. Mater. 2010, 22, 1915–1925.


30

Page 31 of 38

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


(21)

Kakiage, K.; Aoyama, Y.; Yano, T.; Oya, K.; Fujisawa, J.-I.; Hanaya, M. Highly-

Efficient Dye-Sensitized Solar Cells with Collaborative Sensitization by Silyl-Anchor and Carboxy-Anchor Dyes. Chem. Commun. 2015, 15894–15897. (22)

Wu, Y.; Zhu, W. Organic Sensitizers from D–π–A to D–A–π–A: Effect of the Internal

Electron-Withdrawing Units on Molecular Absorption, Energy Levels and Photovoltaic Performances. Chem. Soc. Rev. 2013, 42, 2039–2058. (23)

Wu, Y.; Zhu, W.-H.; Zakeeruddin, S. M.; Grätzel, M. Insight into D–A–π–A Structured

Sensitizers: A Promising Route to Highly Efficient and Stable Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 9307–9318. (24)

Velusamy, M.; Justin Thomas, K. R.; Lin, J. T.; Hsu, Y.-C.; Ho, K.-C. Organic Dyes

Incorporating Low-Band-Gap Chromophores for Dye-Sensitized Solar Cells. Org. Lett. 2005, 7, 1899–1902. (25)

Chou, H.-H.; Chen, Y.-C.; Huang, H.-J.; Lee, T.-H.; Lin, J. T.; Tsai, C.; Chen, K. High-

Performance Dye-Sensitized Solar Cells based on 5,6-Bis-hexyloxy-benzo[2,1,3]thiadiazole. J. Mater. Chem. 2012, 22, 10929–10938. (26)

Kim, J.-J.; Choi, H.; Lee, J.-W.; Kang, M.-S.; Song, K.; Kang, S. O.; Ko, J. A Polymer

Gel Electrolyte to Achieve ≥6% Power Conversion Efficiency with a Novel Organic Dye Incorporating a Low-Band-Gap Chromophore. J. Mater. Chem. 2008, 18, 5223–5229. (27)

Zhu, W.; Wu, Y.; Wang, S.; Li, W.; Li, X.; Chen, J.; Wang, Z.-s.; Tian, H. Organic D–A–

π–A Solar Cell Sensitizers with Improved Stability and Spectral Response. Adv. Funct. Mater. 2011, 21, 756–763.


31


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)

Page 32 of 38

Haid, S.; Marszalek, M.; Mishra, A.; Wielopolski, M.; Teuscher, J.; Moser, J.-E.;

Humphry-Baker, R.; Zakeeruddin, S. M.; Grätzel, M.; Bäuerle, P. Significant Improvement of Dye-Sensitized Solar Cell Performance by Small Structural Modification in π-Conjugated Donor–Acceptor Dyes. Adv. Funct. Mater. 2012, 22, 1291–1302. (29)

Wu, Y.; Zhang, X.; Li, W.; Wang, Z.-S.; Tian, H.; Zhu, W. Hexylthiophene-Featured D–

A–π–A Structural Indoline Chromophores for Coadsorbent-Free and Panchromatic DyeSensitized Solar Cells. Adv. Energy Mater. 2012, 2, 149–156. (30)

Wu, Y.; Marszalek, M.; Zakeeruddin, S. M.; Zhang, Q.; Tian, H.; Grätzel, M.; Zhu, W.

High-Conversion-Efficiency Organic Dye-Sensitized Solar Cells: Molecular Engineering on D–A–π–A Featured Organic Indoline Dyes. Energy Environ. Sci. 2012, 5, 8261–8272. (31)

Lin, R. Y.-Y.; Lee, C.-P.; Chen, Y.-C.; Peng, J.-D.; Chu, T.-C.; Chou, H.-H.; Yang, H.-

M.; Lin, J. T.; Ho, K.-C. Benzothiadiazole-Containing Donor–Acceptor–Acceptor Type Organic Sensitizers for Solar Cells with ZnO Photoanodes. Chem. Commun. 2012, 48, 12071–12073. (32)

Zhang, M.; Wang, Y.; Xu, M.; Ma, W.; Li, R.; Wang, P. Design of High-Efficiency

Organic Dyes for Titania Solar Cells Based on the Chromophoric Core of Cyclopentadithiophene-Benzothiadiazole. Energy Environ. Sci. 2013, 6, 2944–2949. (33)

Cui, Y.; Wu, Y.; Lu, X.; Zhang, X.; Zhou, G.; Miapeh, F. B.; Zhu, W.; Wang, Z.-S.

Incorporating Benzotriazole Moiety to Construct D–A–π–A Organic Sensitizers for Solar Cells: Significant Enhancement of Open-Circuit Photovoltage with Long Alkyl Group. Chem. Mater. 2011, 23, 4394–4401.


32

Page 33 of 38

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


(34)

Mao, J.; Guo, F.; Ying, W.; Wu, W.; Li, J.; Hua, J. Benzotriazole-Bridged Sensitizers

Containing a Furan Moiety for Dye-Sensitized Solar Cells with High Open-Circuit Voltage Performance. Chem. Asian J. 2012, 7, 982–991. (35)

Li, W.; Wu, Y.; Zhang, Q.; Tian, H.; Zhu, W. D–A–π–A Featured Sensitizers Bearing

Phthalimide and Benzotriazole as Auxiliary Acceptor: Effect on Absorption and Charge Recombination Dynamics in Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2012, 4, 1822–1830. (36)

Yen, Y.-S.; Lee, C.-T.; Chen, Y.-C.; Chou, H.-H.; Lin, J.-T. Benzotriazole-Containing

D–π–A Conjugated Organic Dyes for Dye-Sensitized Solar Cells. Chem. Asian J. 2013, 8, 809–816. (37)

Huang, S.-T.; Hsu, Y.-C.; Yen, Y.-S.; Chou, H. S.; Lin J. T.; Chang, C.-W.; Hsu, C.-P.;

Tasi, C.; Yin, D.-J. Organic Dyes Containing a Cyanovinyl Entity in the Spacer for Solar Cells Applications. J. Phys. Chem. C. 2008, 112, 19739–19747. (38)

Chaurasia, S.; Hsu, C.-Y.; Chou, H.-H.; Lin, J. T. Synthesis, Optical and Electrochemical

Properties of Pyridal[2,1,3]thiadiazole Based Organic Dyes for Dye Sensitized Solar Cells. Org. Electron. 2014, 15, 378–390. (39)

Chaurasia, S.; Hung, W. I.; Chou, H. H.; Lin, J. T. Incorporating a New 2H-

[1,2,3]Triazolo[4,5-c]pyridine Moiety to Construct D–A–π–A Organic Sensitizers for High Performance Solar Cells. Org. Lett. 2014, 16, 3052–3055. (40)

Anthony, J. E. Functionalized Acenes and Heteroacenes for Organic Electronics. Chem.

Rev. 2006, 106, 5028–5048.


33


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

(41)

Page 34 of 38

Qiu, Y.; Wei, P.; Zhang, D.; Qiao, J.; Duan, L.; Li, Y.; Gao, Y. Novel Naphtho[2,3-

c][1,2,5]thiadiazole Derivative for Non-doped Small Molecular Organic Red-Light-Emitting Diodes. Adv. Mater. 2006, 18, 1607–1611. (42)

Wei, P.; Duan, L.; Zhang, D.; Qiao, J.; Wang, L.; Wang, R.; Dong, G.; Qiu, Y. A New

Type of Light-Emitting Naphtho[2,3-c][1,2,5]thiadiazole Derivatives: Synthesis, Photophysical Characterization and Transporting Properties. J. Mater. Chem. 2008, 18, 806– 818. (43)

Zhang, Y.; Yang, J.; Hou, Q.; Mo, Y.; Peng, J.; Cao, Y. Near Infrared Polymer Light-

Emitting Diodes. Chin. Sci. Bull. 2005, 50, 957–960. (44)

Sun, Y.; Duan, L.; Wei, P.; Qiao, J.; Dong, G.; Wang, L.; Qiu, Y. An Ambipolar

Transporting Naphtho[2,3-c][1,2,5]thiadiazole Derivative with High Electron and Hole Mobilities. Org. Lett. 2009, 11, 2069–2072. (45)

Q-CHEM, Version 4.0, Shao, Y.; Fusti-Molnar, L.; Jung, Y.; Kussmann, J.; Ochsenfeld,

C.; Brown, S. T.; Gilbert, A. T. B.; Slipchenko, L. V.; Levchenko, S. V.; O’Neill, D. P.; DiStasio, R. A.; Lochan Jr., R. C.; Wang, T.; Beran, G. J. O.; Besley, N. A.; Herbert, J. M.; Lin, C. Y.; Van Voorhis, T.; Chien, S. H.; Sodt, A.; Steele, R. P.; Rassolov, V. A.; Maslen, P. E.; Korambath, P. P.; Adamson, R. D.; Austin, B.; Baker, J.; Byrd, E. F. C.; Dachsel, H.; Doerksen, R. J.; Dreuw, A.; Dunietz, B. D.; Dutoi, A. D.; Furlani, T. R.; Gwaltney, S. R.; Heyden, A.; Hirata, S.; Hsu, C.-P.; Kedziora, G.; Khaliullin, R. Z.; Klunzinger, P.; Lee, A. M.; Lee, M. S.; Liang, W.; Lotan, I.; Nair, N.; Peters, B.; Proynov, E. I.; Pieniazek, P. A.; Rhee, Y. M.; Ritchie, J.; Rosta, E.; Sherrill, C. D.; Simmonett, A. C.; Subotnik, J. E.; Woodcock III, H. L.; Zhang, W.; Bell, A. T.; Chakraborty, A. K.; Chipman, D. M.; Keil, F.


34

Page 35 of 38

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


J.; Warshel, A.; Hehre, W. J.; Gan, Z.; Zhao, Y.; Schultz, N. E.; Truhlar, D.; Epifanovsky, E.; Oana, M.; Baer, R.; Brooks, B. R.; Casanova, D.; Chai, J.-D.; Cheng, C.-L.; Cramer, C.; Crittenden, D.; Ghysels, A.; Hawkins, G.; Hohenstein, E. G.; Kelley, C.; Kurlancheek, W.; Liotard, D.; Livshits, E.; Manohar, P.; Marenich, A.; Neuhauser, D.; Olson, R.; Rohrdanz, M. A.; Thanthiriwatte, K. S.; Thom, A. J. W.; Vanovschi, V.; Williams, C. F.; Wu, Q.; You, Z.Q.; Sundstrom, E.; Parkhill, J.; Lawler, K.; Lambrecht, D.; Goldey, M.; Olivares-Amaya, R.; Bernard, Y.; Vogt, L.; Watson, M.; Liu, J.; Yeganeh, S.; Kaduk, B.; Vydrov, O.; Xu, X.; Zhang, C.; Russ, N.; Zhang, I.Y.; Goddard III, W.A.; Besley, N.; Ghysels, A.; Landau, A.; Wormit, M.; Dreuw, A.; Diedenhofen, M.; Klamt, A.; Lange, A.W.; Ghosh, D.; Kosenkov, D.; Landou, A.; Zuev, D.; Deng, J.; Mao, S.P.; Su, Y.C.; Small D.; H. F. Schaefer III, J. Kong, A. I. Krylov, P. M. W. Gill, and M. Head-Gordon, Q-Chem Inc., Pittsburgh, PA, 2008. (46)

Vaswani, H. M.; Hsu, C.-P.; Head-Gordon, M.; Fleming, G. R. Quantum Chemical

Evidence for an Intramolecular Charge-Transfer State in the Carotenoid Peridinin of Peridinin-Chlorophyll-Protein. J. Phys. Chem. B 2003, 107, 7940–7946. (47)

Kurashige, Y.; Nakajima, T.; Kurashige, S.; Hirao, K.; Nishikitani, Y. Theoretical

Investigation of the Excited States of Coumarin Dyes for Dye-Sensitized Solar Cells. J. Phys. Chem. A 2007, 111, 5544–5548. (48)

Dreuw, A.; Head-Gordon, M. Failure of Time-Dependent Density Functional Theory for

Long-Range Charge-Transfer Excited States: The Zincbacteriochlorin-Bacteriochlorin and Bacteriochlorophyll-Spheroidene Complexes. J. Am. Chem. Soc. 2004, 126, 4007–4016.


35


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

(49)

Page 36 of 38

Balan, A.; Gunbas, G.; Durmus, A.; Toppare, L. Donor−Acceptor Polymer with

Benzotriazole Moiety: Enhancing the Electrochromic Properties of the “Donor Unit”. Chem. Mater. 2008, 20, 7510–7513. (50)

Baran, D.; Balan, A.; Celebi, S.; Esteban, B. M.; Neugebauer, H.; Sariciftci, N. S.;

Toppare, L. Processable Multipurpose Conjugated Polymer for Electrochromic and Photovoltaic Applications. Chem. Mater. 2010, 22, 2978–2987. (51)

Stille, J. K. The Palladium-Catalyzed Cross-Coupling Reactions of Organotin Reagents

with Organic Electrophiles. Angew. Chem. Int. Ed. 1986, 25, 508–524. (52)

Hansch, C.; Leo, A.; Taft, R. W. A Survey of Hammett Substituent Constants and

Resonance and Field Parameters. Chem. Rev., 1991, 91, 165–195. (53)

Cheng, L. T.; Tam, W.; Stevenson, S. H.; Meredith, G. R.; Rikken, G.; Marder, S. R.

Experimental Investigations of Organic Molecular Nonlinear Optical Polarizabilities. 1. Methods and Results on Benzene and Stilbene Derivatives. J. Phys. Chem., 1991, 95, 10631– 10643. (54)

Duan, X. M.; Konami, H.; Okawa, H.; Matsuda, H.; Nakanishi, H. Second-Order

Hyperpolarizabilities of Stilbazolium Cations Studied by Semiempirical Calculation. J. Phys. Chem., 1996, 100, 17780–17785. (55)

Hara, K.; Sato, T.; Katoh, R.; Furube, A.; Ohga, Y.; Shinpo, A.; Suga, S.; Sayama, K.;

Sugihara, H.; Arakawa, H. Molecular Design of Coumarin Dyes for Efficient Dye-Sensitized Solar Cells. J. Phys. Chem. B 2003, 107, 597–606.


36

Page 37 of 38

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


(56)

Hagfeldt, A.; Grätzel, M. Light-Induced Redox Reactions in Nanocrystalline Systems.

Chem. Rev. 1995, 95, 49–68. (57)

Kay, A.; Grätzel, M. Artificial Photosynthesis. 1. Photosensitization of Titania Solar

Cells with Chlorophyll Derivatives and Related Natural Porphyrins. J. Phys. Chem. 1993, 97, 6272–6277. (58)

Hara, K.; Dan-oh, Y.; Kasada, C.; Ohga, Y.; Shinpo, A.; Suga, S.; Sayama, K.; Arakawa,

H. Effect of Additives on the Photovoltaic Performance of Coumarin-Dye-Sensitized Nanocrystalline TiO2 Solar Cells. Langmuir 2004, 20, 4205–4210. (59)

Ito, S.; Miura, H.; Uchida, S.; Takata, M.; Sumioka, K.; Liska, P.; Comte, P.; Péchy, P.;

Grätzel, M. High-Conversion-Efficiency Organic Dye-Sensitized Solar Cells with a Novel Indoline Dye. Chem. Commun. 2008, 5194–5196. (60)

Ko, S.; Choi, H.; Kang, M.-S.; Hwang, H.; Ji, H.; Kim, J.; Ko, J.; Kang, Y. Silole-Spaced

Triarylamine Derivatives as Highly Efficient Organic Sensitizers in Dye-Sensitized Solar Cells (DSSCs). J. Mater. Chem. 2010, 20, 2391–2399. (61)

Koumura, N.; Wang, Z.; Mori, S.; Miyashita, M.; Suzuki, E.; Hara, K. Alkyl-

Functionalized Organic Dyes for Efficient Molecular Photovoltaics. J. Am. Chem. Soc. 2006, 128, 14256–14257. (62)

Koumura, N.; Wang, Z-S.; Miyashita, M.; Sekiguchi, H.; Cui, Y.; Mori, A.; Mori, S.;

Hara, K. Substituted Carbazole Dyes for Efficient Molecular Photovoltaics: Long Electron Lifetime and High Open Circuit Voltage Performance. J. Mater. Chem. 2009, 19, 4829– 4836.


37


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 38 of 38

Table of Contents Graphic


38

Naphtho[2,3-c][1,2,5]thiadiazole and 2H-Naphtho[2 ... - ACS Publications

Recommend Documents