Self-Assembly by Coordination with Organic Antenna Chromophores

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Self-Assembly by Coordination with Organic Antenna Chromophores for Dye-Sensitized Solar Cells Hailang Jia, Zhi-Jie Peng, Shan-Shan Li, Cheng-Yan Huang, and Mingyun Guan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00870 • Publication Date (Web): 08 Apr 2019 Downloaded from http://pubs.acs.org on April 8, 2019

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ACS Applied Materials & Interfaces

Self-Assembly by Coordination with Organic Antenna Chromophores for Dye-Sensitized Solar Cells Hai-Lang Jia,*, 1 Zhi-Jie Peng,1 Shan-Shan Li,1 Cheng-Yan Huang 2 and Ming-Yun Guan*, 1

1

School of Chemical and Environmental Engineering, Institute of Advanced Functional

Materials for Energy, Jiangsu University of Technology, Changzhou 213001, P. R. China.

2

Department of Chemistry, School of Environmental Science and Engineering, Jiangsu Key

Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing University of Information Science & Technology, Nanjing 210044, P. R. China.

KEYWORDS: DSSCs, self-assembly, organic antenna chromophores, anchor, phenothiazine

ABSTRACT

The development of new sensitizers and new sensitization methods is one of the important means to enhance the conversion efficiency of DSSCs, the ultimate goal is to broaden the spectral response of dyes, reduce electron recombination, suppress dye aggregation. In this study, we have developed a series of new self-assembly dyes and applied in DSSCs. We prepared two organic antenna chromophores S1 and S2, and coordinated them with two acceptors A1 and A2

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via zinc to construct A-Zn-S series self-assembled dyes. This method is very simple and feasible, and can avoid the complex synthesis steps of traditional dyes, the results show that the lightharvesting ability of devices can be improved and charge recombination can be reduced by adjusting the structures of the antenna chromophores and acceptors. The device of A2-Zn-S1 gived a PCE of 4.25%, which was higher than those of A1-Zn-S1 (3.88%), A1-Zn-S2 (3.21%) and A2-Zn-S2 (3.52%), the main reason is that the different coordination combinations between the antenna chromophore and the acceptor make a great difference in V oc and Jsc. The device based on A2-Zn-S1 showed a high Voc of 632 mV and a high Jsc of 9.54 mA cm-2, one reason is that S1 has better spectral responsiveness, another reason is that A2 has better steric resistance effectively reduces charge recombination. Besides, the IR indicates that these self-assembly dyes anchored on TiO2 surface by bicarboxyl anchoring group, it is also very beneficial for improving the performance of dyes.

INTRODUCTION

Energy is very important for the global economic, it is an important material basis for the improvement of human living standards and the development of national economy, at present, the world's energy composition is still coal, oil and natural gas and other traditional energy sources, therefore, new energy is of great significance to mankind. Solar energy is abundant in resources and has great potential for development, among them, one of the most important methods is to use solar energy to generate photovoltaic power.1,2 Dye-sensitized solar cells


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(DSSCs) is a new type of solar cells, which was developed by imitating the principle of photosynthesis, it uses low-cost TiO2 and sensitizers as the main raw materials. Its main advantages are abundant raw materials, low price and simple manufacturing technology, which is very suitable for large-scale industrial production.3-6 Since M. Grätzel and co-workers made a breakthrough in this technology in 1991, many researchers have been involved in this research field, after nearly 30 years of development, DSSCs have also made many significant breakthroughs.7-10 In 2014, M. Grätzel and co-workers developed an excellent porphyrin dye, which was named SM315, the corresponding DSSC gived a high PCE, the value achieved 13.0%.11 At the same year, T. Yano et. al developed the dye ADEKA-1 with silyl-anchor, after cosensitized with LEG4, the DSSC exhibited the highest PCE of 14.3%.12 Typical components of DSSCs include conductive glass (FTO), nano-semiconductor electrodes, dyes, electrolytes and counter electrodes, forming sandwich structures. The core idea of DSSCs is to separate the process of light absorption from that of electronic collection, and dyes are mainly used to expand the spectral response range of devices, thus, the improvement of excellent dyes is one of the most important means to improve the performance of DSSCs. 13-16 In recent years, many research groups in the world have designed and synthesized many new dyes for DSSCs, in general, dye with excellent property should meet the following conditions: (1) in the visible region, it should have wide and strong absorption, and its spectral response should reach near infrared region, so that dyes can fully absorb sunlight and enhance the lightharvesting ability of devices, (2) the dye should has excellent light and thermal stability, so that it


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can be recycled to meet the requirements of stability, (3) the dye should has good adsorption performance on the semiconductor surface, it should contain anchoring groups such as carboxyl, phosphoric acid, sulfonic acid or pyridine, (4) the excited dye should has high effective electron injection efficiency, (5) the oxidized dye has high regeneration efficiency, (6) the corresponding life of the excited state of dye is long, the quantum efficiency is high after absorbing sunlight, and the ideal quantum efficiency is 100%.17-20 At present, metal complex dyes and organic dyes are the main sensitizers for DSSCs, many excellent dyes have also been successfully prepared, the PCE of ruthenium complexes N719, K77, C106 and zinc porphyrin dyes YD2-o-C8, LD14, WW6, XW11 are all over 10%.21-27 In recent years, organic dyes have developed vigorously, with the establishment of D-π-A infrastructure, more and more efficient dyes have been prepared, at the same time, these dyes have many advantages, for example, they have high molar extinction coefficient, easy regulation of molecular structure, low cost, good plasticity and easy degradation.28-35 The DSSCs based on triphenylamine dyes C219, TPA-TTAR-T-A, perylene dye C281, indole dye YA422, phenothiazine dye EQ3 all showed a high PCE of over 10%.36-40 In recent years, the design and optimization of dye structure have made great progress in DSSCs, some structures with excellent performance such as D-D-π-A, D-A-π-A, D-π-(A)n have been developed successfully, which can expand the spectral response range of the dyes and improve the short-circuit current (Jsc) of the devices,41-43 meanwhile, introducing long alkyl chain and designing steric resistance effect can reduce charge recombination and increase the open circuit voltage (Voc) of devices. However, there is still a big gap between the current PCE and the


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theoretical PCE, limitation of single-layer dyes has always been one of the bottlenecks in the development of DSSCs, so it is necessary to develop new structure dyes and new sensitization methods. In this work, we developed a new self-assembly dye and applied in DSSCs. This selfassembly strategy eliminates tedious synthesis steps and has a high yield, the technical operation is very simple. Besides, the overall performance of the device can also be optimized by adjusting the structures of antenna molecules or anchor molecules. We prepared two organic antenna chromophores S1 and S2, and coordinated them with two acceptors A1 (2-(4-carboxypyridin-2yl)pyridine-4-carboxylic acid) and A2 (2,2′-Biquinoline-4,4′-dicarboxylic acid) via zinc to construct A-Zn-S series self-assembled dyes (Figure 1). In fact, ruthenium complex dyes with similar structures have been prepared (MC1 and MC3), 44 despite the use of precious ruthenium, the efficiency of the devices is not ideal, especially for MC3, the PCE is only 1.62%. In addition, the two dyes all require lengthy synthesis steps, and the yields of the two dyes are very low (below 40%). Herein, we have developed a simple method for preparing dyes, the cheap zinc chloride is used for dye self-assembly. The device of A2-Zn-S1 gived a PCE of 4.25%, which is higher than those of A1-Zn-S1 (3.88%), A1-Zn-S2 (3.21%) and A2-Zn-S2 (3.52%), the main reason is that the different coordination combinations between the antenna chromophore and the acceptor make a great difference in Voc and Jsc. The optical properties, electrochemical properties, photovoltaic performance of these devices were also measured to study the structure-activity relationship.


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Figure 1 The structures of S1, S2, A1, A2 and YD2-o-C8.

RESULTS AND DISCUSSION

Optical properties

The absorption curves of organic antenna chromophores S1 and S2 were first studied, as shown in Figure 2a, there's a very obvious absorption band in the range of 450-550 nm for the two chromophores, this should be due to the intramolecular charge transfer property (ICT). It is clear that the chromophore S1 exhibits the maximum absorption peak at 493 nm, in addition, the value of absorption coefficient is up to 1.54×104 M-1 cm-1. Although chromophore S2 shows a higher absorption coefficient, the value is up to 1.65×104 M-1 cm-1, compared with that of S1, it is blue-


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shifted about 20 nm, the strongest absorption wavelength of S2 is located at 473 nm, this may be owing to the relatively poor electron-donor performance and conjugate structure of carbazole. In order to further study the changes of absorption spectra after self-assembly, the absorption spectra of A-Zn-S series self-assembled dyes on TiO2 were studied. As shown in Figure 2b, it is clear that the absorption spectra have changed dramatically after self-assembly anchored on TiO2 surface, compared to the spectra in Figure 2a, their absorption spectra have been significantly improved. For the A-Zn-S series self-assembled dyes, on the one hand, the introduction of acceptors A1 (2-(4-carboxypyridin-2-yl)pyridine-4-carboxylic acid) or A2 (2,2′biquinoline-4,4′-dicarboxylic acid) prolong the conjugated system of dyes, on the other hand, due to the coordination of zinc metal, the dyes exhibit strong metal-to-ligand charge transfer (MLCT) character, so the absorption spectra of dyes show a great red shift after self-assembly. Benefiting from the wider spectral responsiveness of S1, the absorption spectral of A1-Zn-S1 and A2-Zn-S1 reached nearly 750 nm, compared with S1, their maximum absorption peaks all were redshifted by nearly 50 nm. The absorption spectral of A1-Zn-S2 and A2-Zn-S2 reached nearly 670 nm, compared with S2, their maximum absorption peaks all were redshifted by nearly 40 nm. After self-coordination with ZnCl2, the spectral response of these dyes has been greatly enhanced, which is helpful to increase the Jsc of devices. In order to prove the role of selfassembly based on zinc coordination, we have designed relevant proof experiments. Firstly, the electrode was immersed into 2 mM A solution (A1 and A2 in DMF) for 12 hours, then washed twice with EtOH and dried, the corresponding absorption curves of A were studied, then


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immersed into S1 (0.4 mM in THF/EtOH=2/1) for 12 hours, then washed twice with EtOH and dried, the corresponding absorption curves of A-S1 were measured. In addition, in order to compare the changes of absorption spectra, we studied the corresponding absorption curves of A1-Zn and A2-Zn. As shown in Figure 1c, the absorption curves of A-S and A-Zn have hardly changed compared with those of A, they hardly absorb in the visible region. The results show that it is very successful to coordinate the antenna chromophores S1 and S2 with acceptors A1 and A2 to construct A-Zn-S self-assembled dyes by zinc metal. Besides, the EDX (energy-dispersive X-ray spectroscopy) was used to further confirm the structures of self-assembled dyes,45 considering that the peak position of N element will be covered by that of Ti element, the atomic ratio of S:Zn can be used to analyze the structure of self-assembled dyes. A2-Zn-S1 on TiO2 film as the test sample, the Figure S1 showed that atomic ratio of S (from S1):Zn (from ZnCl2) was close to 2:1, this also indirectly proves that the self-assembly schematic is correct (Figure S2). In addition, one of the purposes of choosing selfassembly strategy is to avoid tedious synthesis steps and improve the yield of dyes, from Figure S1, we can estimate that the percentage of the formation of A2-Zn-S1 is about 80%, such a simple method can achieve a high coverage, which will greatly exceed the general synthesis yield. To further confirm the structure of self-assembled dyes, the series of A-Zn-S dyes have been synthesized. The yield of each dye is less than 35%, which also proves the superiority of self-assembly strategy. The absorption spectra of the four A-Zn-S dyes were measured in Figure S3, there's a very obvious absorption band for these dyes around 500 nm. It is clear that A1-Zn-


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S1 and A2-Zn-S1 exhibit the maximum absorption peaks at 498 nm and 500 nm, respectively, and the A1-Zn-S2 and A2-Zn-S2 exhibit the maximum absorption peaks at 479 nm and 480 nm, respectively. Compared with the absorption spectra of antenna molecule S, those of selfassembled dyes show obvious red shift. The corresponding emission spectra of A1-Zn-S1, A1Zn-S2, A2-Zn-S1, A2-Zn-S2 were also measured (Figure S4), the values are 595 nm, 623 nm, 596 nm, 621 nm, respectively. Subsequently, we carried out relevant dye desorption experiments. We desorbed self-assembled dyes from the surface of TiO2 and measured their absorption spectra (Figure S5), obviously, their absorption spectra are consistent with those of synthetic AZn-S series dyes, it can be concluded that the structure of self-assembled dyes we inferred is correct. In addition, the amount of dye loading can be estimated from desorption experiments, the values of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1, A2-Zn-S2 are 2.74×10-7mol cm-2, 2.32×10-7mol cm-2, 2.62×10-7mol cm-2, 2.18×10-7mol cm-2, respectively. There is not much difference in the amounts of dye loading, this does not have much impact on their performance.


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Figure 2 (a) Absorption curves of S1 and S2 in dichloromethane, (b) Absorption curves of A1Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2 anchored on TiO2 surface, (c) Absorption curves of A1, A2, A1-S1, A2-S1, A1-Zn and A2-Zn anchored on TiO2 surface. Electrochemical studies One of the prerequisites for excellent dyes is to conform to the energy level matching principle, in general, the excited state energy level of dyes should be negative than -0.5 V (the CB of TiO2 is -0.5 V versus NHE,), and the oxidized potential of dyes should be positive than 0.4 V (the potential of I-/I3- couple is 0.4 V, versus NHE), only in this way can the dyes be guaranteed to


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have both high charge injection efficiency and high dye regeneration efficiency.46,47 The CV (cyclic voltammetry curves) of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2 anchored on TiO2 were investigated to study whether these dyes have high charge injection efficiency from excited dyes to CB of TiO2 (Figure S6). From Figure 3, It can be seen that the EOX of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2 (ground state oxidation potentials) are 0.91 V, 0.98 V, 0.93 V, 1.01 V, respectively. The results indicate the EOX of the four dyes are higher than 0.4 V, this proves that these dyes will have good regeneration efficiency. Besides, we can estimate the energy gap (E0-0) based on their absorption spectra, the EO-O of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2 are about 1.77 V, 1.90 V, 1.77 V, 1.90 V (versus NHE), respectively. Therefore, we can get their E*OX (excited state energy levels of dyes), the values of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2 are -0.86 V, -0.92 V, -0.84 V, -0.89 V, respectively, from these values, we can see that they are negative than CB of TiO2, this also means that they all have good electron injection efficiency. Besides, we also found an interesting phenomenon, either ground


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state oxidation potential or excited oxidation potentials, A1-Zn-S1 and A2-Zn-S1 loses less energy than A1-Zn-S2 and A2-Zn-S2, this makes for increase the efficiency of dye regeneration and charge injection.

Figure 3 Energy diagram of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2

IR spectra analysis In the structural composition of dyes, anchoring groups are very important, which is closely related to the degree of bonding between dyes and semiconductors and the electron injection efficiency. The anchoring modes of these four self-assembled dye molecules were analyzed by infrared spectroscopy (IR), we studied the IR spectra of the A powders and the A-Zn-S selfassembled dyes anchored on TiO2 surface (Figure 4). For powders A1 and A2, we can observe that they have distinct carboxyl stretching vibration (Vc=o) peaks at 1717 cm-1 and 1697 cm-1,


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respectively, due to the conjugation effect caused by two benzene rings for A2, the vibration peak shifts toward low wave number. After anchored on TiO2 surface by self-assembly, it is clear that the carboxyl stretching vibration peaks all disappeared for A1-Zn-S1, A1-Zn-S2, A2Zn-S1 and A2-Zn-S2, the results show that the four dyes are bonded with TiO2 in a doubleanchored adsorption mode. As we known, anchoring groups are very important for structural design of dye molecules, the charge injection efficiency will be greatly affected by the anchoring groups, in addition, the anchors also play a decisive role in the binding energy of the sensitizer on photoanode .48,49 Compared with a single anchor, dyes with multianchor groups will get more efficient electron extraction paths, therefore, the efficiency of electron injection and the adsorption stability of dyes would be increased. Efficient electron injection efficiency is very helpful to improve their IPCE, so the photocurrent of the device will be improved very well. Besides, good adsorption stability can reduce the desorption of dyes, this facilitates charge transfer of the devices and reduces dark current, close-packed dye molecules also help reduce charge recombination, so the photovoltage of the device will also be improved.50,51


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Figure 4 (a) IR spectra of A powders, (b) dyes adsorbed on TiO2

Photovoltaic performance of DSSCs The four self-assembled dyes A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2 were fabricated for DSSCs under the same conditions, we measured their photovoltaic performance and collected photovoltaic parameters in Table 1 from photocurrent-density-photovoltage curves (Figure S7).


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From Table 1, we can see that the power conversion efficiency of A1-Zn-S1(3.88%), A1-Zn-S2 (3.21%) and A2-Zn-S2 (3.52%) are between 3%-4%, obviously, these values are lower than that of A2-Zn-S1 (4.25%), this is mainly due to their great differences in J sc and Voc. For the device of A2-Zn-S1, it has the highest PCE of 4.25%, besides, it shows a high value of J sc (9.62 mA cm2

) and Voc (632 mV). From the previous analysis of optical properties, S1 has better spectral

absorption ability compared to that of S2, after self-assembly with acceptors (A1 and A2), A1Zn-S1 and A2-Zn-S1 still show better spectral responsiveness than those of A1-Zn-S2 and A2Zn-S2, the results also show that dyes containing antenna chromophores S1 may have better light-harvesting ability. On the other hand, either ground state oxidation potential or excited oxidation potentials, A1-Zn-S1 and A2-Zn-S1 loses less energy than those of A1-Zn-S2 and A2Zn-S2, this makes for increase the efficiency of dye regeneration and charge injection. Combine these reasons, it is easy to understand why the Jsc of A1-Zn-S1 (9.12 mA cm-2) and A2-Zn-S1 (9.62 mA cm-2) are both greater than those of A1-Zn-S2 (8.32 mA cm-2) and A2-Zn-S2 (7.76 mA cm-2). In addition, the results show that the Voc of A2-Zn-S1 (632 mV) and A2-Zn-S2 (637 mV) are both greater than those of A1-Zn-S1 (614 mV) and A1-Zn-S2 (601 mV), from this we can also see the importance of dye structure design. Compared with A1, A2 has better stereoscopic effect because of its extended benzene ring, this can prevent I3- from approaching the electron of the TiO2 conduction band, so charge recombination may decrease and the Voc could be improved, the next EIS (Electrochemical Impedance Spectroscopy) tests confirm this inference.


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In addition, we measured the IPCE curves (incident photon-to-current conversion efficiency) of the DSSCs to analyze the differences between their Jsc (Figure 5). Obviously, the IPCE curves of A1-Zn-S1 and A2-Zn-S1 are both broader and higher than those of A1-Zn-S2 and A2-Zn-S2, this trend is consistent with their Jsc. The device of A2-Zn-S1 exhibits the highest value of 45.4%, the photocurrent response range has been reached about 720 nm, and the device of A1-Zn-S1 gets a very similar IPCE curve, with the highest value of 41.5%. The IPCE curves of A1-Zn-S2 and A2-Zn-S2 are very similar, their photocurrent response range all reach up to about 650 nm, the IPCE curve of A1-Zn-S2 is slightly higher than that of A2-Zn-S2, it is consistent with their Jsc. Table 1 Photovoltaic parameters of DSSCs Dye

Jsc (mA cm-2)

Voc (V)

FF (%)

η (%)

A1-Zn-S1

9.12

0.614

69.16

3.88

A1-Zn-S2

8.32

0.601

64.17

3.21

A2-Zn-S1

9.62

0.632

69.80

4.25

A2-Zn-S2

7.76

0.637

71.26

3.52

YD2-o-C8

16.00

0.698

66.39

7.42


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Figure 5 IPCE spectra of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1, A2-Zn-S2, YD2-o-C8. ElS measurements

For DSSCs, Electrochemical Impedance Spectroscopy (EIS) is an important way to study the charge transfer properties at the phase interface. Herein, we used EIS to observe the charge transfer dynamics of these devices under dark. In fact, the Voc would be greatly affected by the electron recombinaton rate.52-54 In order to investigate the difference between Voc, for the EIS measurement, the applied voltage is -0.7 V, the scanning frequency of the devices is from 105 to 1 Hz. As shown in the Nyquist plots of Figure 6a, two semicircles can be seen in these DSSCs, the small semicircle corresponds to the transport resistance at the Pt/electrolyte, the charge transfer resistance at the TiO2/dye/electrolyte interface corresponds to the large semicircle. Clearly, the large semicircles of A2-Zn-S1 and A2-Zn-S2 are both bigger than those of A1-ZnS1 and A1-Zn-S2, in addition, A2-Zn-S1 and A2-Zn-S2 have similar radius, A1-Zn-S1 and A1-


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Zn-S2 have similar radius, this means that A2 is better than A1 in reducing the electron recombination rate, this is conducive to suppressing dark current and improving Voc, this also explains why Voc of A2-Zn-S1 and A2-Zn-S2 are both bigger than those of A1-Zn-S1 and A1Zn-S2. Besides, we also measured the bode phase plots, so we can study the electron lifetimes of the DSSCs (Figure 6b). We know that the longer the electron lifetime, the smaller the dark current, this helps to increase the Voc. Electron lifetime (τ) is an important parameter, according to τ=1/(2πf), we can calculate the lifetimes. The f of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1, A2-Zn-S2 are 32.4 Hz, 37.1 Hz, 19.5 Hz, 20.9 Hz, respectively. so, the values of corresponding electron lifetimes are 4.91 ms, 4.29 ms, 8.16 ms, 7.61 ms, respectively, this is also in line with their Voc trend.


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Figure 6 (a) Nyquist plots of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2, (b) Bode phase plots of A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2. CONCLUSIONS

In summary, we have developed a series of new self-assembly dyes and applied in DSSCs. Two organic antenna chromophores S1 and S2 were synthesized, and coordinated them with two acceptors A1 and A2 via zinc to construct A-Zn-S series self-assembled dyes. The results indicate that light-harvesting ability of devices can be improved and charge recombination can be reduced by adjusting the structures of the antenna chromophores and acceptors. This strategy is highly feasible and easy to operate, and can avoid the complex synthesis steps of traditional dyes. The device of A2-Zn-S1 exhibited the highest value of PCE (4.25%), which is higher than those of A1-Zn-S1 (3.88%), A1-Zn-S2 (3.21%) and A2-Zn-S2 (3.52%), it is mainly due to their great differences in Jsc and Voc, the main reason is that the different coordination combinations


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between the antenna chromophore and the acceptor make different effects. The device of A2-ZnS1 showed a high Voc of 632 mV and a high Jsc of 9.54 mA cm-2, on the one hand, organic antenna chromophores S1 has better spectral responsiveness than that of S2, on the other hand, acceptor A2 has better steric resistance effectively reduces charge recombination, these help to increase Jsc and Voc. In addition, the IR indicates that these self-assembly dyes anchored on TiO2 surface by bicarboxyl anchoring group, it is also very beneficial for improving charge injection efficiency and dye adsorption stability. Thus, self-assembled dyes provide a new design concept for the design of high-efficiency dyes and a new method for improving the performance of DSSCs. EXPERIMENTAL SECTION

Preparation of dyes The scheme S1 of supporting information exhibited the synthetic routes of S1, S2, A1-Zn-S1, A1-Zn-S2, A2-Zn-S1 and A2-Zn-S2, in addition, the support information includes characterization data and synthesis steps. Characterization

The Bruker DRX NMR spectrometer (400 MHz, 500 MHz) was used to record the spectra of 1H NMR and

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C NMR, the TMS was used as the internal standard. The Shimadzu UV-3600

spectrometer was used to study the absorption spectra, the Perkin Elmer LS55 spectrophotometer was used to investigate the emission spectra, the Vector22 spectrometer was used to study the IR


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spectra. We used the Electrochemical Workstation of Chenhua CHI760E (Shanghai) to study the CV and EIS spectra. For the CV measurements, photoanode was used as working electrode, Fc/Fc+ was used as an external reference. We estimate the amount of dye loading by measuring the absorption spectra, a 0.1 M NaOH solution in a mixed solvent (DMF/H2O=3/1) as the desorption solution.

Preparation and measurements of DSSCs The effective area of TiO2 film is 0.196 cm2, which was made by screen printing. The thickness of the TiO2 film is about 12 μm. Before use, the films were washed with deionized water and ethanol, dried, and immersed into TiCl4 solution (40 mM) for 30 min at 700C, then washed with deionized water and ethanol, dried. Then the TiO2 films were prepared by programmed heating in muffle furnace. Firstly, the electrode was immersed into 2 mM A solution (A1 and A2 in DMF) for 12 hours, then washed twice with EtOH and dried, then immersed into 2 mM ZnCl 2 solution (MeOH) for 1 hours, washed twice with EtOH and dried, and then soaked into 0.4 mM S solution (THF/EtOH=2/1) for 12 hours, washed twice with EtOH and dried. The sensitized photoanode is packaged with the Pt counter electrode by 25 μm Surlyn film, then the electrolyte is injected by vacuum pumping. The composition of the electrolyte includes 50 mM LiI, 50 mM I2, 0.1 M GuNCS, 0.5 M tert-butylpyridine, 0.6 M BMII in anhydrous acetonitrile. The Keithley 2400 source meter under AM 1.5G solar to measured the I-V curves, we used a DC method to measure the IPCE spectra, the light was supplied by a 300 W xenon lamp.


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ASSOCIATED CONTENT

Supporting Information

Synthesis details and characterization data, and cyclic voltammogram experiments. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by grants from the National Natural Science Foundation of China (21701060) and Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (17KJB150015, 18KJA150003). REFERENCES 1. Hagfeldt, A.; Hagfeldt, G.; Sun, L. C.; Kloo, L.; Pettersson, H. Dye-Sensitized Solar Cells. Chem. Rev. 2010, 110, 6595-6663.


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Self-Assembly by Coordination with Organic Antenna Chromophores

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