Benzothiadiazole Versus Thiophene: Influence ... - Wiley Online Library

Communication Solar Cells

www.mrc-journal.de

Benzothiadiazole Versus Thiophene: Influence of the Auxiliary Acceptor on the Photovoltaic Properties of Donor–Acceptor-Based Copolymers Zongbo Li, Kangkang Weng, Aihua Chen,* Xiaobo Sun,* Donghui Wei, Mingming Yu, Lijun Huo,* and Yanming Sun* due to its distinct properties.[40] With an additional D or A unit in the polymer backbone, the new polymer can possess the advantages of the known D and A moieties. Accordingly, the properties of terpolymers can be finely tuned through selecting the appropriate third component.[41–48] Recently, Huang and co-workers have synthesized a new terpolymer, PTB7-Th-T2, which showed a high PCE of 8.9%.[49] Na and co-workers reported two terpolymers with benzodithiophene and thiophene used as the third component.[50] The terpolymers also yielded PCEs over 8%. Therefore, terpolymer has been a promising approach to develop novel conjugated polymers for PSCs. Inspired by the results, in this contribution, we present two novel copolymers, P1 and P2 (see Scheme 1). P1 is a typical D–A alternating copolymer with thiophene derivatives as the donor unit and T1 as the acceptor unit. P2 is a D–A1–D–A2 type copolymer, in which a well-known electron-deficient moiety, benzothiadiazole (BT), was introduced to replace the thiophene unit as the third component. The properties of the two copolymers were systematically investigated and compared.

Two donor–acceptor (D–A) type conjugated copolymers, P1 and P2, are designed and synthesized. A classical benzothiadiazole acceptor is used to replace a thiophene unit in the polymer chain of P1 to obtain P2 terpolymer. Compared with P1, P2 exhibits broader absorption spectra, higher absorption coefficient, deeper lowest unoccupied molecular orbital level, and a relatively lower band gap. As a result, the P2-based solar cell exhibits a high power conversion efficiency (PCE) of 6.60%, with a short-circuit current (Jsc) of 12.43 mA cm−2, and a fill factor (FF) of 73.1%, which are higher than those of the P1-based device with a PCE of 4.70%, a Jsc of 9.43 mA cm−2, and an FF of 61.6%.

1. Introduction Solution-processed bulk-heterojunction polymer solar cells (PSCs) have made enormous progress over the past decades, with the high power conversion efficiency (PCE) exceeding 12%.[1–8] The rapid increases in PCEs are partially attributed to the significant developments of photovoltaic materials, especially the donor–acceptor (D–A)-type conjugated copolymers.[9–35] Among the high-performance conjugated D–A copolymers, the electron-withdrawing unit of 1,3-bis(2-ethylhexyl)benzo[1,2c:4,5-c′]dithio-phene-4,8-dione (T1) has been widely used.[36–38] Up to now, the highest PCE of T1-based copolymer has already exceeded 10%.[36] However, in most cases, the T1 unit has been used to construct wide-bandgap polymers. Narrow-bandgap polymers based on the T1 unit are rare.[39] Recently, terpolymer, which consists of three distinct monomers in the polymer backbone, has attracted much attention Z. Li, Prof. A. Chen School of Materials Science and Engineering Beihang University Xueyuan Road 37, Haidian District, Beijing 100191, P. R. China E-mail: [email protected] K. Weng, Prof. X. Sun, Prof. L. Huo, Prof. Y. Sun School of Chemistry Beihang University Xueyuan Road 37, Haidian District, Beijing 100191, P. R. China E-mail: [email protected]; [email protected]; [email protected] Prof. D. Wei, Prof. M. Yu The College of Chemistry and Molecular Engineering Zhengzhou University Zhengzhou, Henan Province 450001, P. R. China The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/marc.201700547.

DOI: 10.1002/marc.201700547

Macromol. Rapid Commun. 2017, 1700547

2. Results and Discussion 2.1. Synthesis and Thermal Properties As shown in Scheme 1, compound 1–3 were synthesized according to the literature.[51–53] The T1 unit (compound 6) was synthesized via a cyclization reaction.[51] Compounds 7a and 7b were synthesized using compound 3 and brominated compound 6 via a classical Stille coupling with Pd(PPh3)4 as the catalyst, and the dibrominated compounds 8a or 8b were synthesized by utilizing N-bromosuccinimide to add a Br group at the α position of compound 7a or 7b. Finally, P1 and P2 were achieved through a traditional Stille coupling by using compound 8 and commercial monomers. P1 and P2 are soluble in common organic solvents, such as chloroform, chlorobenzene, and o-dichlorobenzene. The number-average molecular weight (Mn) and the polydispersity index were tested by gel permeation chromatography using a polystyrene standard in a chloroform eluent, and the values are 31.2 k, 5.4 and 29.1 k, 3.1 for P1 and P2, respectively. Thermal properties of P1 and P2 were evaluated using thermogravimetric analysis at a heating rate of 10 °C min−1

1700547 (1 of 6)

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.mrc-journal.de

www.advancedsciencenews.com

Scheme 1. Synthetic routes of P1 and P2.

under nitrogen atmosphere. The 5% weight loss of the two polymers P1 and P2 are at 427 and 433 °C, respectively, indicating their excellent thermal stabilities (Figure S1, Supporting Information).

2.2. Optical Properties The normalized UV–vis absorption spectra of P1 and P2 solution and thin film are shown in Figure 1a. The optical properties are listed in Table S1 in the Supporting Information. In a diluted solution, the main absorption peaks of P1 and P2 are located at 505 and 589 nm, respectively. Compared with P1, P2 shows obvious broader absorption band and a relatively redshifted peak, which is mainly due to the strong electronwithdrawing property of BT.[54] In addition, P2 possessed a prominent shoulder peak at 687 nm, implying its aggregation even in solution.[55] In thin films, the main absorption peaks of


P1 and P2 are redshifted to 582 and 627 nm, respectively, which can be ascribed to favorable molecular ordering in the solid state.[56] The onset values of absorption spectra of P1 and P2 in the films is 720 and 780 nm, corresponding to the optical band gaps of 1.72 and 1.59 eV, respectively. The polymer P2 shows a lower band gap. The extinction coefficient in the solid state is calculated with the highest absorption peak (Figure 1b). The value of P2 is 5.38 × 104 cm−1, which is higher than that of P1 (4.54 × 104 cm−1).

2.3. Theoretical Simulation Density functional theory (DFT) calculations were performed at B3LYP/6–31G(d,p) level to further investigate the geometrical configuration and electronic property of the polymers. The optimized geometries of the polymers are listed in Figure S2 in the Supporting Information. Both of the polymers show planar

1700547 (2 of 6)



www.mrc-journal.de

Normalized Absorption (a.u.)

1.4 1.2

P1 in solution P2 in solution P1 in film P2 in film

(a)

1.0 0.8 0.6 0.4 0.2 0.0 400

500

600

700

800

Absorption coefficient(106 M-1cm-1)

Wavelength (nm) 6 5

P1 P2

(b)

4 3

CV curves of the two polymers are displayed in Figure S4a in the Supporting Information, and the data are summarized in Table S1 in the Supporting Information. The Ag/Ag+ electrode is used as the reference electrode and ferrocene/ferrocenium (Fc/Fc+) electrode is used as the standard electrode. The potential of the Fc/Fc+ is 0.4 eV with respective to the Ag/Ag+ reference electrode. Under such measurement conditions, the onset reduction potentials of polymer P1 and P2 are −0.84 and −0.78 V, respectively. The onset oxidation potentials of the two polymers are 0.94 and 0.98 V, respectively. Based on the equation HOMO = −(Eox + 4.4) eV and LUMO = −(Ered + 4.4) eV, the HOMO/LUMO levels of P1 and P2 are −5.34/−3.56 and −5.38/−3.62 eV, respectively. In contrast with P1, the HOMO and LUMO levels of P2 are downshifted, which can be attributed to the high electronegativity of the nitrogen atoms in the BT unit. And, the value of the declined LUMO level in P2 is much greater than that of decreased HOMO level, which may suggest that BT has a tendency to lower the LUMO level. The electrochemical bandgaps of P1 and P2 are −1.78 and −1.76 eV. The difference between the electrochemical band gap and optical band gap can be ascribed to the exciton binding energy.[57,58]

2.5. Hole Mobility

2 1 0 400

500

600

700

800

Wavelength (nm) Figure 1. a) UV–vis absorption spectra of P1 and P2 solutions and thin films. b) The absorption coefficient of P1 and P2 thin films.

geometrical backbones. The simulated dihedral torsion angles between the adjacent aromatic units are 15°/13°/43°/19° and 6.0°/0.3°/37°/21° for P1 and P2, respectively. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) electron density distributions are shown in Figure S3 in the Supporting Information. The HOMO distributions of the two polymers are mainly localized on the entire molecular backbones. As for the LUMO distributions, big differences between the two polymers were observed. For polymer P1, the LUMO distribution is localized on both the donors (oligothiophene) and the T1 unit. However, the LUMO distribution of P2 is entirely on the acceptor BT unit. From the DFT calculations, P2 has a lower LUMO energy level at −2.82 eV. The results indicated that the molecular structure and electron density distributions could be finely tuned by introducing an additional acceptor in polymer backbone.

2.4. Electrochemical Properties The HOMO and LUMO levels were also measured using electrochemical cyclical voltammetry (CV) measurements. The


The hole mobilities of the two polymers were investigated through the space-charge-limited current method. The hole-only device structure is indium tin oxide (ITO)/MoOx/polymers:PC71BM/MoOx/Al. The J–V curves under dark conditions were profiled in Figure S5 in the Supporting Information. The hole mobility of P2 is 1.29 × 10−4 cm2 V−1 s−1, and is increased to 3.11 × 10−4 cm2 V−1 s−1 with 1,8-diiodooctane (DIO) additive. The hole mobility of P1 is also increased from 1.91 × 10−4 to 4.77 × 10−3 cm2 V−1 s−1 when 1% DIO was used. Moreover, the mobilities of the neat polymers were measured using organic field-effect transistors (OFETs). The devices exhibited typical p-type transport properties. P1 shows a mobility of 3.6 × 10−3 cm2 V−1 s−1, which is slightly higher than that of P2 (2.3 × 10−3 cm2 V−1 s−1).

2.6. Photovoltaic Properties To evaluate the photovoltaic properties, PSCs with a traditional device structure of ITO/poly(3,4-ethylenedioxythiophene):poly(s tyrene sulfonate)/polymer:PC71BM/Ca/Al were fabricated. The photovoltaic properties were measured under an illumination of AM 1.5 G simulated solar light at 100 mW cm−2. The different weight ratios of donor and acceptor as well as the different concentrations of the additives have been tested. The results of PSCs under the optimal conditions are showed in Figures S6–S9 in the Supporting Information and data are summarized in Tables S2 and S3 in the Supporting Information. The different weight ratios of polymers:PC71BM films were initially used to optimize the devices. The optimal weight ratios of P1: PC71BM and P2: PC71BM is found to be 1.5:1 and 1:2, respectively. A traditional solvent additive (DIO) was used to optimize the active layer morphology. As shown in Figures S7

1700547 (3 of 6)


www.mrc-journal.de


2

Current Density (mA/cm )

(a)

2 0 P1 P2

-2 -4 -6 -8 -10 -12 0.0

(b)

0.2

0.4 0.6 Voltage (V)

60

0.8

P1 P2

EQE (%)

50 Figure 3. TEM images of a) P1:PC71BM blend film, b) P2:PC71BM blend film, c) P1:PC71BM blend film with 1% DIO, and d) P2:PC71BM blend film with 3% DIO.

40 30

from EQE agrees well with the values obtained from the J–V curves.

20 10 0 300

2.7. Film Morphology

400

500 600 700 Wavelength (nm)

800

Figure 2. a) J–V and b) EQE curves of PSCs based on P1:PC71BM and P2:PC71BM blend films under the optimal conditions.

and S9 in the Supporting Information, DIO has a dramatic impact on the photovoltaic performance of P2, especially on Jsc and fill factor (FF). The Jsc for P2-based devices was increased from 9.30 to 12.15 mA cm−2 and FF was increased from 64.7% to 73.0%. However, the effect of DIO on the Jsc and FF of P1-based devices is moderate. The optimal volume of DIO additive for P1- and P2-based devices is found to be 1% and 3%, respectively. The average device parameters of devices based on P1 and P2 are summarized in Table S4 in the Supporting Information. P2 showed a higher PCE of 6.6%, with a Jsc of 12.15 mA cm−2 and an FF of 73.0%. Interestingly, despite its relatively higher HOMO level, P1 achieved a relatively higher Voc of 0.82 V, which is probably due to the high charge transfer state (ECT) of P1: PC71BM.[59,60] The higher Jsc achieved in the P2based device can be ascribed to its broader absorption spectra. As shown in Figure 2b, the external quantum efficiencies (EQEs) of the champion devices for P1 and P2 were recorded. The EQE value of P2 is higher than 50% in the wavelength range of 400–660 nm, and the maximum value is up to 56%. For P1, the EQE value is higher than 50% in the region from 420 to 500 nm and the maximum value is up to 51%. As a result, P2 shows a higher photocurrent. The Jsc value calculated


It is well known that the morphology of the active layer is crucially important for PSCs, which can affect the exciton dissociation, charge transport, and charge recombination. Herein, the morphology of the blend films was investigated using atomic force microscopy (AFM), and transmission electron micro scopy (TEM). Figure S10 in the Supporting Information showed the AFM height images of the polymer:PC71BM blend films. Without using DIO, the surfaces of the blend films are relatively smooth with the room-mean-square (RMS) of surface roughness of 1.06 and 0.99 nm for P1 and P2 blend films, respectively. With DIO, the RMS values were increased to 4.61 nm for P1 blend films and 5.69 nm for P2 blend films. The TEM images were shown in Figure 3. Compared with P1 blend, P2 blend shows clear fibril structures within the whole film. It is known that the fibril morphology is favorable for charge transport.[61] As a result, the P2-based device showed a higher photovoltaic performance (see Tables S2 and S3, Supporting Information). When DIO was used as the additive, both P1 and P2 blend films showed fibril-like aggregates and increased phase separation (Figure S5c,d, Supporting Information). Accordingly, the PCEs of P1 and P2 devices were significantly improved.

3. Conclusion In conclusion, by introducing an electron-withdrawing BT unit into the polymer chain of P1, P2 terpolymer was synthesized.

1700547 (4 of 6)



www.mrc-journal.de

Compared with P1, P2 showed broader absorption spectra, higher absorption coefficient, and a lower band gap. PSCs based on P2 showed a PCE of 6.6% with a higher Jsc of 12.15 mA cm−2 and a higher FF of 74%, which are higher than those of P1-based devices. The results indicate that incorporating an additional electron-withdrawing unit into a traditional D–A polymer is a practical and promising synthetic strategy for developing high-performance photovoltaic polymers.

Supporting Information Supporting Information is available from the Wiley Online Library or from the author.

Acknowledgements Z.L. and K.W. contributed equally to this work. This work was financially supported by the National Natural Science Foundation of China (NSFC) (Nos. 51472018, 51272010, 51473009, and 21674007), Beijing Nova Program (No. XX2013009). The authors are grateful to Prof. Y. Guo and Prof. Y. Liu for the OFET measurements.

Conflict of Interest The authors declare no conflict of interest.

Keywords benzothiadiazole, organic solar cells, power conversion efficiency, terpolymers Received: August 9, 2017 Revised: September 7, 2017 Published online:

[1] S. H. Park, A. Roy, S. Beaupré, S. Cho, N. Coates, J. S. Moon, D. Moses, M. Leclerc, K. Lee, A. J. Heeger, Nat. Photonics 2009, 3, 297. [2] Z. Li, K. Jiang, G. Yang, J. Y. Lai, T. Ma, J. Zhao, W. Ma, H. Yan, Nat. Commun. 2016, 7, 13094. [3] L. Y. Lu, T. Xu, W. Chen, E. S. Landry, L. P. Yui, Nat. Photonics. 2014, 8, 716. [4] S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv. Mater. 2016, 28, 9423. [5] Z. C. He, B. Xiao, F. Liu, H. B. Wu, Y. L. Yang, S. Xiao, C. Wang, T. P. Russell, Y. Cao, Nat. Photonics 2015, 9, 174. [6] J. You, L. Dou, K. Yoshimura, T. Kato, K. Ohya, T. Moriarty, K. Emery, C. C. Chen, J. Gao, G. Li, Y. Yang, Nat. Commun. 2013, 4, 1446. [7] Y. Shin, C. E. Song, W. H. Lee, S. K. Lee, W. S. Shin, I. N. Kang, Macromol. Rapid Commun. 2017, 38, 1700016. [8] F. Y. Xie, D. He, H. Pan, J. X. Jiang, L. M. Ding, Macromol. Rapid Commun. 2017, 38, 1700074. [9] L. Dou, C.-C. Chen, K. Yoshimura, K. Ohya, W.-H. Chang, J. Gao, Y. Liu, E. Richard, Y. Yang, Macromolecules 2013, 46, 3384. [10] T. L. Nguyen, H. Choi, S. J. Ko, M. A. Uddin, B. Walker, S. Yum, J. E. Jeong, M. H. Yun, T. J. Shin, S. Hwang, J. Y. Kim, H. Y. Woo, Energy Environ. Sci. 2014, 7, 3040. [11] C. Cui, W.-Y. Wong, Y. Li, Energy Environ. Sci. 2014, 7, 2276. [12] L. Lu, L. Yu, Adv. Mater. 2014, 26, 4413.


[13] Y. F. Li, Acc. Chem. Res. 2012, 45, 723. [14] L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao, L. Yu, Chem. Rev. 2015, 115, 12666. [15] Y. Huang, F. Liu, X. Guo, W. Zhang, Y. Gu, J. Zhang, C. C. Han, T. P. Russell, J. Hou, Adv. Energy Mater. 2013, 3, 930. [16] J. S. Wu, S. W. Cheng, Y. J. Cheng, C. S. Hsu, Chem. Soc. Rev. 2015, 44, 1113. [17] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science 1995, 270, 1789. [18] Z. C. He, C. M. Zhong, X. Huang, W. Y. Wong, H. B. Wu, L. W. Chen, S. J. Su, Y. Cao, Adv. Mater. 2011, 23, 4636. [19] C. H. Cui, Z. C. He, Y. Wu, X. Cheng, H. B. Wu, Y. F. Li, Y. Cao, W. Y. Wong, Energy Environ. Sci. 2016, 9, 885. [20] C. H. Cui, W. Y. Wong, Macromol. Rapid Commun. 2016, 37, 287. [21] W. Y. Wong, X. Z. Wang, Z. He, A. B. Djurisic, C. T. Yip, K. Y. Cheung, H. Wang, C. S. K. Mak, W. K. Chan, Nat. Mater. 2007, 6, 521. [22] W. Y. Wong, C. L. Ho, Acc. Chem. Res. 2010, 43, 1246. [23] W. Y. Wong, X. Z. Wang, Z. He, K. K. Chan, A. B. Djurisic, K. Y. Cheung, C. T. Yip, A. M. C. Ng, Y. Y. Xi, C. S. K. Mak, W. K. Chan, J. Am. Chem. Soc. 2007, 129, 14372. [24] L. Liu, C. L. Ho, W. Y. Wong, K. Y. Cheung, M. K. Fung, W. T. Lam, A. B. Djurisic, W. K. Chan, Adv. Funct. Mater. 2008, 18, 2824. [25] Q. Wang, W. Y. Wong, Polym. Chem. 2011, 2, 432. [26] W. Y. Wong, Macromol. Chem. Phys. 2008, 209, 14. [27] C. J. Qin, Y. Y. Fu, C. H. Chui, C. W. Kan, Z. Y. Xie, L. X. Wang, W. Y. Wong, Macromol. Rapid Commun. 2011, 32, 1472. [28] X. Z. Wang, Q. W. Wang, L. Yan, W. Y. Wong, K. Y. Cheung, A. N. Ng, A. B. Djurisic, W. K. Chan, Macromol. Rapid Commun. 2010, 31, 861. [29] C. L. Ho, Z. Q. Yu, W. Y. Wong, Chem. Soc. Rev. 2016, 45, 5264. [30] S. Liu, P. You, J. Li, J. Li, C. S. Lee, B. S. Ong, C. Surya, F. Yan, Energy Environ. Sci. 2015, 8, 1463. [31] H. Zhou, Y. Zhang, C. K. Mai, S. D. Collins, G. C. Bazan, T. Q. Nguyen, A. J. Heeger, Adv. Mater. 2015, 27, 1767. [32] H. Chen, Y. Guo, G. Yu, Y. Zhao, J. Zhang, D. Gao, H. Liu, Y. Liu, Adv. Mater. 2012, 24, 4618. [33] H. Hu, K. Jiang, G. Yang, J. Liu, Z. Li, H. Lin, Y. Liu, J. Zhao, J. Zhang, F. Huang, Y. Qu, W. Ma, H. Yan, J. Am. Chem. Soc. 2015, 137, 14149. [34] J. Zhao, Y. Li, A. Hunt, J. Zhang, H. Yao, Z. Li, J. Zhang, F. Huang, H. Ade, H. Yan, Adv. Mater. 2016, 28, 1868. [35] Q. Tao, Y. Xia, X. Xu, S. Hedström, O. Bäcke, D. I. James, P. Persson, E. Olsson, O. Inganäs, L. Hou, W. Zhu, E. Wang, Macromolecules 2015, 48, 1009. [36] T. Liu, X. X. Pan, X. Y. Meng, Y. Liu, D. H. Wei, W. Ma, L. J. Huo, X. B. Sun, T. H. Lee, M. Huang, H. Choi, J. Y. Kim, W. C. H. Choy, Y. M. Sun, Adv. Mater. 2017, 29, 1604251. [37] Y. Ie, J. M. Huang, Y. Uetani, M. Karakawa, Y. Aso, Macromolecules 2012, 45, 4564. [38] L. Huo, T. Liu, X. Sun, Y. Cai, A. J. Heeger, Y. Sun, Adv. Mater. 2015, 27, 2938. [39] H. Zhang, S. Zhang, K. Gao, F. Liu, H. Yao, B. Yang, C. He, T. P. Russell, J. Hou, J. Mater. Chem. A 2017, 5, 10416. [40] T. E. Kang, K. H. Kim, B. J. Kim, J. Mater. Chem. A 2014, 2, 15252. [41] W. W. Li, K. H. Hendriks, A. Furlan, A. D. Zhang, M. M. Wienk, R. A. J. Janssen, Chem. Commun. 2015, 51, 4290. [42] J. W. Jung, F. Liu, T. P. Russell, W. H. Jo, Energy Environ. Sci. 2013, 6, 3301. [43] T. Qin, W. Zajaczkowski, W. Pisula, M. Baumgarten, M. Chen, M. Gao, G. Wilson, C. D. Easton, K. Mullen, S. E. Watkins, J. Am. Chem. Soc. 2014, 136, 6049. [44] K. H. Hendriks, G. H. Heintges, V. S. Gevaerts, M. M. Wienk, R. A. Janssen, Angew. Chem, Int. Ed. 2013, 52, 8341. [45] I. E. Kuznetsov, A. V. Akkuratow, D. K. Susarova, D. V. Anokhin, Y. L. Moskvin, M. V. Kluyev, A. S. Peregudov, P. A. Troshin, Chem. Commun. 2015, 51, 7562.

1700547 (5 of 6)


www.mrc-journal.de

www.advancedsciencenews.com [46] B. B. Fan, X. N. Xue, X. Y. Meng, X. B. Sun, L. J. Huo, W. Ma, Y. M. Sun, J. Mater. Chem. A 2016, 4, 13930. [47] C. L. Chochos, S. Drakopoulou, A. Katsouras, B. M. Squeo, C. Sprau, A. Colsmann, V. G. Gregoriou, A. P. Cando, S. Allard, U. Scherf, N. Gasparini, N. Kazerouni, T. Ameri, C. J. Brabec, A. Avgeropoulos, Macromol. Rapid Commun. 2017, 38, 1600720. [48] Y. J. Ji, C. Y. Xiao, G. H. L. Heintges, Y. G. Wu, R. A. J. Janssen, D. Q. Zhang, W. P. Hu, Z. H. Wang, W. W. Li, J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 34. [49] T. Jiang, J. Yang, Y. Tao, C. Fan, L. Xue, Z. Zhang, H. Li, Y. Li, W. Huang, Polym. Chem. 2016, 7, 926. [50] Y. S. Lee, J. Y. Lee, S. M. Bang, B. Lim, J. Lee, S. I. Na, J. Mater. Chem. A 2016, 4, 11439. [51] D. Qian, L. Ye, M. Zhang, Y. Liang, L. Li, Y. Huang, X. Guo, S. Zhang, Z. Tan, J. Hou, Macromolecules 2012, 45, 9611. [52] J. Zhou, S. Xie, E. F. Amond, M. L. Becker, Macromolecules 2013, 46, 3391. [53] J. F. Hai, B. F. Zhao, E. W. Zhu, L. Y. Bian, H. B. Wu, W. H. Tang, Macromol. Chem. Phys. 2013, 214, 2473.


[54] J. Du, M. C. Biewer, M. C. Stefan, J. Mater. Chem. A 2016, 4, 15771. [55] Q. Fan, W. Su, X. Guo, Y. Wang, J. Chen, C. Ye, M. Zhang, Y. Li, J. Mater. Chem. A 2017, 5, 9204. [56] J. Du, A. Fortney, K. E. Washington, C. Bulumulla, P. Huang, D. Dissanayake, M. C. Biewer, T. Kowalewski, M. C. Stefan, ACS Appl. Mater. Interfaces 2016, 8, 33025. [57] P. S. Huang, J. Du, S. S. Gunathilake, E. A. Rainbolt, J. W. Murphy, K. T. Black, D. Barrera, J. W. P. Hsu, B. E. Gnade, M. C. Stefan, M. C. Biewer, J. Mater. Chem. A 2015, 3, 6980. [58] D. Gao, G. L. Gibson, J. Hollinger, P. Li, D. S. Seferos, Polym. Chem. 2015, 6, 3353. [59] K. Vandewal, K. Tvingstedt, A. Gadisa, O. Inganas, J. V. Manca, Nat. Mater. 2009, 8, 904. [60] K. Vandewal, Z. Ma, J. Bergqvist, Z. Tang, E. Wang, P. Henriksson, K. Tvingstedt, M. R. Andersson, F. Zhang, O. Inganäs, Adv. Funct. Mater. 2012, 22, 3480. [61] G. P. Kini, S. Oh, Z. Abbas, S. Rasool, M. Jahandar, C. E. Song, S. K. Lee, W. S. Shin, W. W. So, J. C. Lee, ACS Appl. Mater. Interfaces 2017, 9, 12617.

1700547 (6 of 6)
