物理化学学报 >> 2019, Vol. 35 >> Issue (3): 257-267.doi: 10.3866/PKU.WHXB201803191

所属专题: 非富勒烯有机太阳能电池

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以绕丹宁和噻唑烷-2, 4-二酮为端基的不对称结构有机受体分子的设计合成与构性关系探讨

杨阳1,蒋秀1,占肖卫2,*(),陈兴国1,*()   

  1. 1 有机高分子光电功能材料湖北省重点实验室,武汉大学化学与分子科学学院,武汉 430072
    2 北京大学工学院材料科学与工程系,北京 100871
  • 收稿日期:2018-02-01 发布日期:2018-08-28
  • 通讯作者: 占肖卫,陈兴国 E-mail:xwzhan@pku.edu.cn;xgchen@whu.edu.cn
  • 基金资助:
    国家自然科学基金(51173138)

Designing an Organic Acceptor with Unsymmetrical Structure Based on Rhodanine and Thiazolidine-2, 4-dione Units to Study the Structure–Property Relationship

Yang YANG1,Xiu JIANG1,Xiaowei ZHAN2,*(),Xingguo CHEN1,*()   

  1. 1 Hubei Key Laboratory on Organic and Polymeric Opto-electronic Materials, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P. R. China
    2 Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, P. R. China
  • Received:2018-02-01 Published:2018-08-28
  • Contact: Xiaowei ZHAN,Xingguo CHEN E-mail:xwzhan@pku.edu.cn;xgchen@whu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(51173138)

摘要:

分别以绕丹宁和噻唑烷-2, 4-二酮单元为端基、IDT为中心核设计合成了一个新型不对称结构的有机小分子受体IDT-2,并通过与两端均以绕丹宁或噻唑烷-2, 4-二酮受体单元的对称小分子受体IDT-1和IDT-3进行对比,探讨了分子结构与性能之间的关系。研究发现,从IDT-1到IDT-3,随着两端的绕丹宁基团被噻唑烷-2, 4-二酮基团逐步取代,这类小分子受体的吸收光谱显著蓝移,光学带隙Egopt逐步增大,LUMO和HOMO能级也逐渐抬升。随后我们分别以这三个小分子为受体、P3HT为给体共混构建活性层而制备了有机太阳能电池,结果表明,以两端均为绕丹宁单元的对称结构小分子受体IDT-1构建的电池器件具有最高的光电转换效率(PCE),相应的Jsc和FF值也最大,而Voc则最低;而以两端均为噻唑烷-2, 4-二酮基团的对称结构小分子受体IDT-3的电池器件,其Voc最高,但其Jsc和FF则最低,PCE值也最小。对于IDT-2而言,由于分子只有一个绕丹宁单元被噻唑烷-2, 4-二酮所取代,其VocJsc和PCE均介于IDT-1与IDT-3之间。由此说明,尽管噻唑烷-2, 4-二酮基团的引入能有效提升器件Voc,但却不利于改善其Jsc和FF,因此受体的分子设计中如何平衡电池器件的几种光伏性能参数而获得高的光电转换效率仍是十分重要的研究课题之一。

关键词: 不对称结构分子, 绕丹宁单元, 噻唑烷-2, 4-二酮单元, 有机受体分子, 有机太阳能电池

Abstract:

As reported previously, rhodanine and thiazolidine-2, 4-dione units have been widely used as the terminal group to construct the efficient non-fullerene small molecular acceptors with the structure of A1-A2-D-A2-A1. Compared with the acceptor using thiazolidine-2, 4-dione unit as the terminal group, the acceptor with rhodanine unit as the terminal electron-withdrawing group usually showed the improved short circuit current density (Jsc) and fill factor (FF) as well as the higher power conversion efficiency (PCE), regardless of the lower open circuit voltage (Voc). However, the causes of difference are still not very clear. Therefore, in this work, an unsymmetrical organic acceptor (IDT-2) has been designed and synthesized with rhodanine and thiazolidine- 2, 4-dione units as the electron-withdrawing terminal groups to connect an indacenodithiophene (IDT) central core, respectively. By comparing with the two analogues of the symmetrical organic acceptors based on rhodamine unit (IDT-1) or thiazolidine-2, 4-dione unit (IDT-3) as the terminal group, the structure-property relationship has been investigated for this series of acceptors. It is found that as two rhodamine terminal groups are replaced step by step with the thiazolidine-2, 4-dione unit from IDT-1 to IDT-3, the ICT absorption of these small molecular acceptors is significantly blue-shifted from 633 (soln)/656 (film), 618/645 to 603/625 nm, and the corresponding optical band gap (Egopt) is also gradually widened from 1.68, 1.71 to 1.77 eV for IDT-1, IDT-2 and IDT-3, respectively, which can be attributed to the introduction of thiazolidine-2, 4-dione unit to reduce the stability of quinoid structure of the conjugation backbone. At the same time, the LUMO/HOMO (the lowest unoccupied molecular orbital/the highest occupied molecular orbital) energy levels of the molecules are gradually uplifted to be -3.62/-5.58, -3.60/-5.56, and -3.57/-5.53 eV, respectively, which is generally beneficial for the improvement of the Voc due to the upshifted LUMO energy levels of the acceptors. Considering the complementary absorption and well-matched energy levels of the donor and acceptor, the regioregular poly(3-hexylthiophene) (P3HT) has been chosen as a donor to fabricate the devices with three small molecular acceptors, respectively, and the corresponding photovoltaic performances have been evaluated and compared. The device based on IDT-1 with two rhodamine terminal groups gives the best PCE of 4.52% with the lowest Voc of 0.87 V, the highest FF of 70.66% and Jsc of 7.37 mA·cm-2, while the device based on IDT-3 with two thiazolidine-2, 4-dione terminal groups shows the poorest PCE of 3.40% with the highest Voc of 0.98 V but the lowest FF of 59.70% and Jsc of 5.82 mA·cm-2. As for IDT-2 with an unsymmetrical structure, it contains a thiazolidine-2, 4-dione terminal group and a rhodamine terminal group at the two sides of the molecule. It can be seen that the IDT-2 based device just shows a PCE of 4.07% with a Voc of 0.91 V, a FF of 64.65% and a Jsc of 6.81 mA·cm-2, all of which are between those of the devices based on IDT-1 and IDT-3. These results indicate that the thiazolidine-2, 4-dione unit is an effective terminal group to enhance the Voc of the device but is not beneficial to the improvement of the Jsc and FF. Furthermore, when designing the structure of the acceptors, it is very important to maintain the balance of all the three parameters to maximize the PCE in the OSCs.

Key words: Unsymmetric structure, Rhodanine unit, Thiazolidine-2, 4-dione unit, Small molecule acceptor, Organic solar cells

MSC2000: 

  • O646