High-efficiency quaternary polymer solar cells enabled with binary fullerene additives to reduce nonfullerene acceptor optical band gap and improve carriers transport |
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| Authors: | Weiping Li Dong Yan Feng Liu Thomas Russell Chuanlang Zhan Jiannian Yao |
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| Institution: | 1.Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry,Chinese Academy of Sciences,Beijing,China;2.Department of Physics and Astronomy, and Collaborative Innovation Center of IFSA (CICIFSA),Shanghai Jiaotong University,Shanghai,China;3.Department of Polymer Science and Engineering, Room A516, Conte Research Center,University of Massachusetts Amherst,Amherst,USA;4.University of Chinese Academy of Sciences,Beijing,China |
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| Abstract: | The polymer/small-molecule electron donor and nonfullerene organic electron acceptor are of structural similarity with both donor and acceptor molecules consisting of polycyclic fused-ring backbone and being decorated with alkyl-chains. In this study, we report that the introduction of binary fullerenes (C60-/C70-PCBM and C60-/C70-ICBA) into a nonfullerene binary system PBDB-T:ITIC reduces the polymer-nonfullerene acceptor intermixing, obtaining higher crystallinity with (100) crystal coherence length from 28 to 29–33 nm for the ITIC, and from 14 to 20–24 nm for the PBDB-T, and improved electron and hole mobilities both. Unprecedentedly, such a protocol reduces the ITIC optical band gap from 1.59 to 1.55 eV. As consequences, higher short-circuit current-density (17.8–18.4 vs. 15.8 mA/cm2), open-circuit voltage (0.92 vs. 0.90 V) and fill-factor (0.72–0.73 vs. 0.68) are simultaneously obtained, which ultimately afford higher efficient quaternary polymer solar cells with power conversion efficiencies (PCEs) up to 12.0%–12.8% comparing to the host binary device with 9.9% efficiency. For the polymer, ITIC, and ICBA/PCBM ternary blends, 11% PCEs were recorded. The use of PCBM leads to larger red-shifting in thin film absorption and external quantum efficiency (EQE) response. Such effect is more pronounced when ICBA:PCBM mixture is used. These results indicate the size and shape of C60 and C70 as well as the substituent position of the second indene unit on C60-/C70-ICBA affect not only the blend morphology but also the electronic coupling in BHJ mixtures: the quaternary device performance increased in sequences of C70-PCBM:C70-ICBA→C70-PCBM:C60-ICBA→C60-PCBM:C70-ICBA→C60-PCBM: C60-ICBA. The resonant soft X-ray scattering (RSoXS) data indicated the most refined phase separation in the C60-PCBM:C60- ICBA based blend, corresponding to its best device function among the quaternary devices. These results indicate that the using of binary fullerenes as the acceptor additives allows for tuning nonfullerene blended film’s optical properties and film-morphologies, shedding light on the designing high-performance multi-acceptor polymer solar cells. |
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