Acta Chim. Sinica ›› 2017, Vol. 75 ›› Issue (5): 464-472.DOI: 10.6023/A17020074 Previous Articles     Next Articles



竹芯a, 朱凯b, 孙邦锦a, 樊健a, 周祎b, 宋波b   

  1. a. 江苏省碳基功能材料与器件重点实验室 苏州大学功能纳米与软物质研究院 苏州纳米科技协同创新中心 苏州 215123;
    b. 苏州大学材料与化学化工学部 苏州 215123
  • 投稿日期:2017-02-23 发布日期:2017-04-12
  • 通讯作者: 樊健,宋波;
  • 基金资助:


Comprehensive Study of the Effect of DPE Additive on Photovoltaic Performance of 5,6-Difluoro-benzo[1,2,5]thiadiazole Based Donor-acceptor Copolymers

Zhu Xina, Zhu Kaib, Sun Bangjina, Fan Jiana, Zhou Yib, Song Bob   

  1. a. Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123, China;
    b. College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
  • Received:2017-02-23 Published:2017-04-12
  • Contact: 10.6023/A17020074;
  • Supported by:

    Project supported by the National Natural Science Foundation of China (21472135, 51303118, 51673139, 91333204), the Natural Science Foundation of Jiangsu Province of China (BK20151216, BK20161211), the Collaborative Innovation Center of Suzhou Nano Science and Technology (CIC-Nano), Soochow University, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials.

Three donor-acceptor polymers PBT2F-TT-a, PBT2F-TT and PBT2F-Se were synthesized via Stille cross-coupling reaction with 5,6-difluoro-benzo[1,2,5]thiadiazole as the acceptor, and 2,5-bis-(2-octyl-dodecyloxy)-1,4- di(thieno[3,2-b]thiophen-2-yl)-benzene and 2,5-bis-(2-octyl-dodecyloxy)-1,4-di(selenophen-2-yl)-benzene as the donors. The conjugated backbones of these polymers were decorated with alkoxyl groups to achieve the chain planarity through S…O and Se…O intramolecular interactions. Furthermore, the intramolecular F…H interaction was helpful to minimize the torsional angles. These three polymers were characterized by UV-vis absorption spectroscopy, thermal gravimetric analysis, cyclic voltammetry, gel permeation chromatography and elemental analysis. All the polymers showed intense absorption in the visible range and demonstrated suitable ELUMO and EHOMO, which match well with the fullerene-based acceptor. Thus these three polymers were applied as donors and incorporated with PC71BM as active materials in bulk heterojunction polymer solar cells (PSCs). Polymers PBT2F-TT-a and PBT2F-TT are constructed with the same monomers and the latter has a high molecular weight. A notable enhancement in PCE from 3.48% to 4.22% was observed as the molecular weight was increased from 6.79 kDa (PBT2F-TT-a) to 10.36 kDa (PBT2F-TT). The effect of diphenyl ether (DPE) additive on photovoltaic performance of PSCs based on these polymers has been comprehensively investigated by means of atomic force microscopy (AFM), transmission electron microscopy (TEM), alternating current impedance spectrometry (ACIS), space-charge-limited current (SCLC) analysis and short circuit current density - light intensity (JSC-Plight) measurement. As revealed by AFM and TEM measurement, PBT2F-Se:PC71BM blend with DPE exhibited a nanoscale phase separation dominated with fibrillar structures. On the other hand, the charge carrier mobilities of these blend films were greatly increased after the addition of DPE, giving rise to enhanced photovoltaic performances. Furthermore, the dramatic increase in JSC of PBT2F-Se-based devices should also benefit from the well-balanced hole and electron mobilities as revealed by SCLC results. Interestingly, JSC-Plight measurement suggested the weak bimolecular recombination for these devices without and with the addition of DPE. PSCs based on PBT2F-TT-a, PBT2F-TT, and PBT2F-Se showed good power conversion efficiency. Particularly, PBT2F-Se: PC71BM blend with DPE exhibited a good device performance with JSC of 10.75 mA/cm2, VOC of 0.72 V and PCE of 4.18%.

Key words: polymer solar cells, diphenyl ether, fluorinated acceptor, intra-chain interaction, balanced charge transportation