Ternary System with Intermolecular Hydrogen Bond: Efficient Strategy

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Ternary System with Intermolecular Hydrogen-Bond: Efficient Strategy to High Performance Nonfullerene Organic Solar Cells Xinrui Li, Xiaoyang Du, Hui Lin, Xiao Kong, Lijuan Li, Lei Zhou, Cai-Jun Zheng, and Silu Tao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b02121 • Publication Date (Web): 08 Apr 2019 Downloaded from http://pubs.acs.org on April 8, 2019

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ACS Applied Materials & Interfaces

Ternary System with Intermolecular Hydrogen-Bond: Efficient Strategy to High Performance Nonfullerene Organic Solar Cells Xinrui Li, Xiaoyang Du, Hui Lin,* Xiao Kong, Lijuan Li, Lei Zhou, Caijun Zheng, and Silu Tao*

School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, P. R. China

ABSTRACT: In order to boost OSCs performance, numerous approaches have been developed, such as synthesizing new materials, using post-annealing (thermal or solvent annealing) or fabricating ternary devices. The ternary strategy is usually used as an uncomplicated and effective way but how to choose the third component and the effect of interactions between materials on OSCs performance still need to be clarified. Herein, we proposed a new finding that the carbonyl group of ITIC end groups can react with the dye molecule SR197 to form the N–H … O non-covalent interaction. The existence of intermolecular hydrogen bonds was confirmed via FT-IR spectra and 2D-HNMR. The power conversion efficiency (PCE) was improved to 10.29% via doping SR197 into blends of PTB7-Th: ITIC, which exhibited a huge enhancement of approximately 30% compare with the binary OSCs (PCE=7.92%). The ternary OSCs of PBDB-T: SR197: ITIC could also achieve highly PCE (11.03%) without postthermal or solvent annealing. TEM and GIWAXS showed the optimized morphology and enhanced crystallinity of ternary systems, which is facilitated to exciton dissociation and charge transmission. These conclusions mean that H-bonding strategy is an effective way for selecting the third component and could achieve high performance of OSCs.

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KEYWORDS: ternary OSCs, hydrogen bond, nonfullerene acceptor, small molecule, bulk heterojunction 1. INTRODUCTION Recently, organic solar cells (OSCs) have drew increasingly consideration as one of the most promising sustainable energy techniques by reason of their numerous benefits, like light weight, flexibility, inexpensive etc.1-6 Normally, the polymer and fullerene derivative constitute active layer of OSCs.7-12 However, the farther expansion of fullerene OSCs faces great challenges, in part due to their weak light absorption and large energy losses.13 In contrast, nonfullerene acceptors have developed rapidly due to their have good absorption, handily adjusted energy levels, reduced voltage loss, etc.14-16 And they were successfully studied and applied in OSCs, like ITIC which can be used with multiple polymer donors.17-18 However, it is required further study on how to boost the performance of OSCs that based ITIC, due to the electron mobility of ITIC is still low.19-20 So as to obtain high PCE, numerous strategies have been employed, such as using thermal or solvent annealing, fabricating tandem OSCs or mixing a third component to the blends.21-27 Among them, the former two strategies need high fabrication cost and have complex preparation processes. In contrast, ternary OSC is a simple and efficient method that is conducive to the future industrial manufacturing and production.28-34 Typically, the photon harvesting of active layers and the morphological distribution can be finely adjusted by adding a third component with complementary absorption spectrum.35-39 Here, we proposed a novel and simple method to select the third component which could form intermolecular hydrogen bonds with a nonfullerene acceptor. For the non-fullerene based OSCs, the charge


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dissociation and transfer can be improved via introducing an H-bonding to possess enhanced charge extraction efficiency. In this regard, the dye molecule SR197 (Figure 1) was employed as the third component, and the N–H … O non-covalent interaction was formed between the N–H group of SR197 with the carbonyl group of ITIC. NF OSCs achieved highly performance about stability and efficiency simultaneously by incorporating SR197 into the dominate system of PTB7-Th: ITIC. Compare with the binary OSCs(PCE=7.92%), the best PCE of ternary OSCs reach 10.29%, which exhibited a huge enhancement by approximately 30%, and the exciton separation, charge transportation, charge collection of OSCs are both improved. We also prepared PBDB-T: ITIC-based OSCs to further confirm this strategy. Devices treated by SR197 also exhibited a similar trend that achieved high PCE of 11.03% without postannealing (thermal/solvent treatment). Furthermore, an inferior PCE of 8.94% was got when using methanol (MeOH) as an inhibitor of H-bonding into the active layers. These results prove that the H-bonding strategy is a valid way to enhance the performance of devices. 2. EXPERIMENTAL SECTION 2.1 Material preparation We bought PTB7-th, PBDB-T and ITIC at Organtecsolar Material Inc. We bought MoO3 and PEDOT: PSS at Xi’an p-OLED Technology Corp. SR197 (C23H19N5O2) was bought at TCI Corp. If not stated specially, all solvents and chemicals were obtained at Sigma-Aldrich Co. 2.2Device fabrication The ITO glass was washed by ultrasonic with detergent water, ethanol, acetone, and isopropyl alcohol, successively. After UV process for 30 min, ZnO was covered



on it through spin-coating then annealing at 200 °C for 1 h to form ETL with thickness is around 30 nm. Donor (PTB7-Th with 0, 5, 10, 15 or 20 wt% SR197) and acceptor ITIC were mixed in CB (Donor: Acceptor = 1:1.3, 25 mg/mL in whole) with agitating at 70 °C stay over. Donor (PBDB-T with 0, 3, 5, 8 or 10 wt%SR197) and acceptor ITIC were mixed in CB (Donor: Acceptor =1:1, 20 mg/mL in whole) with agitating at 50 °C stay over. The blend solutions were then covered onto ETL through spin-coating in a N2 atmosphere. For PTB7-Th: ITIC system, active layers with and without SR197 all yielded similar thickness is around 80 nm. For PBDB-T: ITIC system, active layers with thicknesses is around 75 nm. Finally, about 10-nanometerthick MoO3 and 150-nanometer-thick Ag were covered successively through evaporating to form the hole transport layer and the electrode. (Under vacuum 13.7% by integrating the advantages of the materials and two binary cells. Energy Environ. Sci. 2018,11, 2134-2141. (23) Li, G.; Shrotriya, V.; Huang, J. S.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nature mater. 2005,4, 864-868. (24) Lu, X. H.; Hlaing, H.; Germack, D. S.; Peet, J.; Jo, W. H.; Andrienko, D.; Kremer, K.; Ocko, B. M. Bilayer order in a polycarbazole-conjugated polymer. Nat. commun. 2012,3, 795. (25) Sun, Y. M.; Welch, G. C.; Leong, W. L.; Takacs, C. J.; Bazan, G. C.; Heeger, A. J. Solution-processed small-molecule solar cells with 6.7% efficiency. Nature mater. 2012,11, 44-48. (26) Xiao, Z. G.; Yuan, Y. B.; Yang, B.; VanDerslice, J.; Chen, J. H.; Dyck, O.; Duscher, G.; Huang, J. S. Universal Formation of Compositionally Graded Bulk Heterojunction for Efficiency Enhancement in Organic Photovoltaics. Adv. Mater. 2014,26, 3068-3075. (27) Du, X.; Liu, B.; Li, L.; Kong, X.; Zheng, C.; Lin, H.; Tong, Q.; Tao, S.; Zhang, X. Excimer emission induced intra-system self-absorption enhancement – a novel strategy to realize high efficiency and excellent stability ternary organic solar cells processed in green solvents. J. Mater. Chem. A 2018,6, 23840-23855. (28) Khlyabich, P. P.; Burkhart, B.; Thompson, B. C. Compositional Dependence of the Open-Circuit Voltage in Ternary Blend Bulk Heterojunction Solar Cells Based on Two Donor Polymers. J. Am. Chem. Soc. 2012,134, 9074-9077. (29) Chen, X. W.; Tao, S. L.; Fan, C.; Chen, D. C.; Zhou, L.; Lin, H.; Zheng, C. J.; Su, S. J. Ternary Organic Solar Cells with Coumarin7 as the Donor Exhibiting Greater Than 10% Power Conversion Efficiency and a High Fill Factor of 75. ACS appl. mater. interfaces 2017,9, 29907-29916. (30) Chen, Y.; Ye, P.; Zhu, Z. G.; Wang, X.; Yang, L.; Xu, X.; Wu, X.; Dong, T.; Zhang, H.; Hou, J.; Liu, F.; Huang, H. Achieving High-Performance Ternary Organic Solar Cells through Tuning Acceptor Alloy. Adv. Mater. 2017,29, 1603154. (31) Street, R. A.; Davies, D.; Khlyabich, P. P.; Burkhart, B.; Thompson, B. C. Origin of the Tunable Open-Circuit Voltage in Ternary Blend Bulk Heterojunction Organic Solar Cells. J. Am. Chem. Soc. 2013,135, 986-989. (32) Zhang, G.; Zhang, K.; Yin, Q.; Jiang, X. F.; Wang, Z.; Xin, J.; Ma, W.; Yan, H.; Huang, F.; Cao, Y. High-Performance Ternary Organic Solar Cell Enabled by a Thick Active Layer Containing a Liquid Crystalline Small Molecule Donor. J. Am. Chem. Soc. 2017,139, 2387-2395. (33) Lin, Y.-C.; Cheng, H.-W.; Su, Y.-W.; Lin, B.-H.; Lu, Y.-J.; Chen, C.-H.; Chen, H.C.; Yang, Y.; Wei, K.-H. Molecular engineering of side chain architecture of conjugated polymers enhances performance of photovoltaics by tuning ternary blend structures. Nano Energy 2018,43, 138-148. (34) Savoie, B. M.; Dunaisky, S.; Marks, T. J.; Ratner, M. A. The Scope and Limitations of Ternary Blend Organic Photovoltaics. Advanced Energy Materials 2015,5, 1400891. (35) Ameri, T.; Khoram, P.; Min, J.; Brabec, C. J. Organic Ternary Solar Cells: A Review. Adv. Mater. 2013,25, 4245-4266. (36) An, Q.; Zhang, J.; Gao, W.; Qi, F.; Zhang, M.; Ma, X.; Yang, C.; Huo, L.; Zhang, F. Efficient Ternary Organic Solar Cells with Two Compatible Non-Fullerene Materials as One Alloyed Acceptor. Small 2018, 14, 1802983.



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TOC 82x44mm (300 x 300 DPI)


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Ternary System with Intermolecular Hydrogen Bond: Efficient Strategy

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