萘酰亚胺取代修饰4,4′-螺双环戊并[2,1-b∶3,4-b′]二噻吩化合物的合成制备及其在有机薄膜光伏器件中的应用研究

近年来,新型有机非富勒烯受体的开发极大地促进了有机聚合物太阳能电池效率的不断突破。其中具有空间非平面结构的新型非富勒烯受体材料是该领域的一个研究热点。本文选取1,8-萘酰亚胺(NMI)作为受电子单元,合成制备了基于螺4,4]双环戊2,1-b∶3,4-b′]二噻吩核心单元的空间非平面化合物SCPDT-(NMI)4及对应的基于环戊2,1-b∶3,4-b′]二噻吩以及环戊2,1-b∶3,4-b′]二噻吩-4-酮的线性模型化合物CPDT-(NMI)2和CPDT-O-(NMI)2。在此基础上,详细研究了3个化合物的光谱吸收、荧光光谱以及循环伏安电化学性质。结果表明,具有螺形结构的SCPDT-(NMI)4因其非平面结构以及较高的分子内空间位阻,导致其吸收光谱与线性化合物CPDT-(NMI)2相比出现了11nm的蓝移。固体薄膜吸收光谱结果表明,这一系列化合物具有弱的分子间相互作用。电化学循环伏安测试结果表明,所合成的3个化合物均有可逆的氧化还原过程。据此测得化合物的LUMO能级大致为-3.5~-3.8eV之间,可作为电子受体用于有机薄膜光伏电池。利用所合成的萘酰亚胺修饰的化合物作为电子受体,PBDB-T作为电子给体制备了有机太阳能电池器件。器件实验结果表明,基于空间非平面SCPDT-(NMI)4的器件光电转换效率达到了1.16%,远高于以线性分子CPDT-(NMI)_2作为受体的器件效率(0.11%)。荧光光谱猝灭实验结果表明,所合成的萘酰亚胺化合物与聚合物之间不完全的电子转移是影响器件性能的最主要因素。

Synthesis and Properties of 4,4'-Spiro-bi[cyclopenta[2,1-b;3,4-b']dithiophene] Cored 1,8-Naphthalimide Derivatives for Organic Solar Cells

With the rapid development of high performance non-fullerene electron acceptor,the power conversion efficiency of polymer solar cells increased dramatically in the last few years,among which structurally non-planar electron acceptors play a very important role.In this paper,a new family non-fullerene electron acceptor based on 1,8-naphthalimide unit with cyclopenta 2,1-b;3,4-b'] dithiophene (CPDT-(NMI) 2),4,4'-spiro-bi cyclopenta2,1-b;3,4-b'] dithiophene] (SCPDT-(NMI)4) or 4-H-cyclopenta-2,l-b;3,4-b'] dithiophene-4-one (CPDT-O-(NMI)2) core were synthesized.The absorption and fluorescence spectra,as well as the electrochemical properties of these compounds were characterized.Results showed that SCPDT-(NMI)4 showed a blue-shifted absorption compared to that of CPDT-(NMI)2,which is ascribed to the twisted molecular structure of CPDT-(NMI)2 for its high steric hindrance.While CPDT-O-(NMI)2 showed two absorption bands with peaking wavelength at 420 nm and 550 nm,which is quite different to that of SCPDT-(NMI)4 and CPDT-(NMI)2.Solid state absorption spectra confirm that SCPDT-(NMI)4 and CPDT-(NMI)2 showed low intermolecular interaction,which could be attributed to the non-planar molecular structure of these two compounds as well.Fluorescence of the SCPDT-(NMI)4 film was found to be red-shifted 11 nm over CPDT-(NMI)2,which is ascribed to the spiro-conjugation effect of SCPDT-(NMI)4 in excited state.Cyclic voltammetry results demonstrated that LUMO energy levels of these compounds are around-3.5 to-3.8 eV,making them suitable electron acceptor in polymer solar cells.Polymer solar cell using PBDB-T as the electron donor and SCPDT-(NMI)4 as the electron acceptor showed a high power conversion efficiency of 1.16 ％,which is much higher than that of CPDT-(NMI)2 (0.11％).Fluorescence of the blended films confirmed that photon induced electron transfer between PBDB-T and NMIs is not completed,which is believed to be one of the main reason for the low device performance.