Efficient and Stable Ternary Organic Solar Cells Based on Two Planar

Wang, Jiajun Peng, Xiaoyu Liu, and Ziqi Liang. Department of Materials Science, Fudan University, Shanghai 200433, China. ACS Appl. Mater. Interfa...
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Efficient and Stable Ternary Organic Solar Cells Based on Two Planar Nonfullerene Acceptors with Tunable Crystallinity and Phase Miscibility Jialin Wang, Jiajun Peng, Xiaoyu Liu, and Ziqi Liang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 01 Jun 2017 Downloaded from http://pubs.acs.org on June 1, 2017

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Efficient and Stable Ternary Organic Solar Cells Based on Two Planar Nonfullerene Acceptors with Tunable Crystallinity and Phase Miscibility Jialin Wang, Jiajun Peng, Xiaoyu Liu and Ziqi Liang* Department of Materials Science, Fudan University, Shanghai 200433, China

ABSTRACT: Planar perylene diimides (PDI), when used as nonfullerene acceptors for organic photovoltaics, are constrained by their large π-aggregation in solid state. To tackle this issue, another planar nonfullerene acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) with weak crystallinity and near-infrared light absorption is introduced into the PTB7Th:PDI binary blend to fabricate efficient and stable ternary solar cells. We have finely tuned the PDI/ITIC weight ratio to investigate the influences of individual ITIC and PDI on the optical, electronic and morphological properties of PTB7-Th:ITIC:PDI ternary blend. Compared to the binary blend, complementary optical absorption is achieved in all ternary blends. More importantly, it is found that ITIC plays a critical role on largely suppressing the PDI aggregates in PTB7-Th:PDI blend, while PDI aids to form an interpenetrating network morphology to facilitate charge transport in PTB7-Th:ITIC blend. Consequently, when the PDI/ITIC ratio is 3:7 (w/w), the PTB7-Th:ITIC:PDI based inverted solar cells exhibit the highest power conversion

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efficiency of 8.64% due to their favorable out-of-plane π-π stacking, finest phase-separation morphology and highest charge mobility. Remarkably, the optimal cells that are solutionprocessed in air show the promising efficiency of 7.09%, suggesting good ambient stability of such ternary solar cells. KEYWORDS: ternary organic solar cells, planar perylene diimide, aggregation, phase miscibility, air stability

1. INTRODUCTION Perylene diimides (PDIs) are considered as potential alternatives to fullerene based acceptors in organic solar cells (OSCs) owing to their high electron affinity similar to fullerene derivatives, large optical extinction coefficients, high electron mobilities and great photochemical stability.1–4 However, their applications for bulk-heterojunction (BHJ) OSCs are now largely staggered by the strong π-aggregation in solid state, especially in planar PDIs molecules, which may form unfavorable blend film morphology with submicrometer-scale PDI domains and thus result in the excimer and incomplete exciton dissociation.5–7 To date, planar PDI-based OSCs have utilized paradigm donor polymers such as poly(3-hexylthiophene) (P3HT),8,9 poly({4,8-bis[(2ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)-carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7),10 pseudo-two-dimensional (2D) conjugated polymers with alkylthienyl side chains such as PBDTTT-C-T,11 along with small molecule donor.12 Most of them exhibited low power conversion efficiency (PCE) of less than 4% with short-circuit current density (JSC) 10%. Adv. Mater. 2016, 28, 10008– 10015. (29) Qin, Y.; Uddin, M. A.; Chen, Y.; Jang, B.; Zhao, K.; Zheng, Z.; Yu, R.; Shin, T. J.; Woo, H. Y.; Hou, J. Highly Efficient Fullerene-Free Polymer Solar Cells Fabricated with Polythiophene Derivative. Adv. Mater. 2016, 28, 9416–9422. (30) Zhang, H.; Li, S.; Xu, B.; Yao, H.; Yang, B.; Hou, J. Fullerene-Free Polymer Solar Cell Based on a Polythiophene Derivative with an Unprecedented Energy Loss of Less Than 0.5 eV. J. Mater. Chem. A 2016, 4, 18043–18049. (31) Zheng, Z.; Awartani, O. M.; Gautam, B.; Liu, D.; Qin, Y.; Li, W.; Bataller, A.; Gundogdu, K.; Ade, H.; Hou, J. Efficient Charge Transfer and Fine-Tuned Energy Level Alignment in a THF-Processed Fullerene-Free Organic Solar Cell with 11.3% Efficiency. Adv. Mater. 2017, 29, 1604241.

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(32) Gupta, V.; Bharti, V.; Kumar, M.; Chand, S.; Heeger, A. J. Polymer–Polymer Förster Resonance Energy Transfer Significantly Boosts the Power Conversion Efficiency of BulkHeterojunction Solar Cells. Adv. Mater. 2015, 27, 4398–4404. (33) Bi, P.-Q.; Wu, B.; Zheng, F.; Xu, W.-L.; Yang, X.-Y.; Feng, L.; Zhu, F.; Hao, X.-T. An Obvious Improvement in the Performance of Ternary Organic Solar Cells with “Guest” Donor Present at the “Host” Donor/Acceptor Interface. ACS Appl. Mater. Interfaces 2016, 8, 23212– 23221. (34) Aluicio-Sarduy, E.; Singh, R.; Kan, Z.; Ye, T.; Baidak, A.; Calloni, A.; Berti, G.; Duò, L.; Iosifidis, A.; Beaupré, S.; Leclerc, M.; Butt, H.-J.; Floudas, G.; Keivanidis, P. E. Elucidating the Impact of Molecular Packing and Device Architecture on the Performance of Nanostructured Perylene Diimide Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 8687–8698. (35) Zhang, J.; Zhang, Y.; Fang, J.; Lu, K.; Wang, Z.; Ma, W.; Wei, Z., Conjugated PolymerSmall Molecule Alloy Leads to High Efficient Ternary Organic Solar Cells. J. Am. Chem. Soc. 2015, 137, 8176–8183. (36) Lin, Y.; Wang, J.; Zhang, Z.-G.; Bai, H.; Li, Y.; Zhu, D.; Zhan, X. An Electron Acceptor Challenging Fullerenes for Efficient Polymer Solar Cells. Adv. Mater. 2015, 27, 1170–1174. (37) Zheng, Z.; Awartani, O. M.; Gautam, B.; Liu, D.; Qin, Y.; Li, W.; Bataller, A.; Gundogdu, K.; Ade, H.; Hou, J. Efficient Charge Transfer and Fine-Tuned Energy Level Alignment in a THF-Processed Fullerene-Free Organic Solar Cell with 11.3% Efficiency. Adv. Mater. 2017, 29, 1604241. (38) Sun, D.; Meng, D.; Cai, Y.; Fan, B.; Li, Y.; Jiang, W.; Huo, L.; Sun, Y.; Wang, Z. NonFullerene-Acceptor-Based Bulk-Heterojunction Organic Solar Cells with Efficiency over 7%. J. Am. Chem. Soc. 2015, 137, 11156–11162.

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(39) Wang, J.; Peng, J.; Sun, Y.; Liu, X.; Chen, Y.; Liang, Z. FAPbCl3 Perovskite as Alternative Interfacial Layer for Highly Efficient and Stable Polymer Solar Cells. Adv. Electron. Mater. 2016, 2, 1600329. (40) Shoaee, S.; Deledalle, F.; Tuladhar, P. S.; Shivanna, R.; Rajaram, S.; Narayan, K. S.; Durrant, J. R. A Comparison of Charge Separation Dynamics in Organic Blend Films Employing Fullerene and Perylene Diimide Electron Acceptors. J. Phys. Chem. Lett. 2015, 6, 201–205.

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Ternary blend cells based on two stable planar nonfullerene acceptors of PDI and ITIC with complementary optical absorption and crystallinity exhibit the PCEs of 8.64% and 7.09% in N2 and air, respectively.

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