基于苯并二噻吩的氟代小分子给体的合成、表征及光伏性能研究

Fluorinated Small Molecular Donors Based on Benzodithiophene:Synthesis,Characterizations and Photovoltaic Performance

对小分子给体进行氟代,往往能够通过拉深其最高占据分子轨道(HOMO)能级来提高光伏器件的开路电压,从而有助于获得更高的光电转化效率。本工作设计合成了含3′,4′-二氟-3,3″-二辛基三联噻吩结构的新型共轭单元,并通过Stille偶联、Knoevenegal缩合等反应进一步合成了以噻吩取代侧链的苯并二噻吩为核心、氟代三联噻吩为共轭桥、罗丹宁为封端基团的新型小分子电子给体光伏材料(命名为BDT4F-RO)。此分子的结构和初步的理化性能分别通过核磁共振波谱(^(1)H NMR、^(13)C NMR、^(19)F NMR)、紫外-可见吸收光谱、循环伏安法和热重分析等进行测试表征。结果表明:薄膜状态下的BDT4F-RO在300~700 nm均有较强的吸收,吸收边界位于690 nm。与不含氟原子的类似物BDT-RO相比,BDT4F-RO具有较深的HOMO能级,这也使得对应的光伏器件有更高的开路电压(0.95 V)。但是总体的效率上BDT4F-RO远逊于BDT-RO,这可能是氟原子的引入使得BDT4F-RO与受体分子IDIC的混溶性较差所致。

The open circuit voltage of photovoltaic devices can often be improved by decreasing the highest occupied molecular orbital(HOMO)energy level,through the fluorination of small molecule donors,which is beneficial to obtaining higher photoelectric conversion efficiency(PCE).In this work,a new conjugated linker containing 3′,4′-difluoro-3,3″-dioctyltrithiophene unit was designed and synthesized.Through the Stille coupling,Knoevenegal condensation reactions and some other reactions,a new small molecule electron donor(namely BDT4F-RO)that with benzodithiophene substituted side chain as the core,fluoro tribithiophene as the conjugate bridge and rhodanine as the end group was synthesized.The molecular structure and properties were preliminarily characterized by NMR spectroscopy(1H NMR,^(13)C NMR and ^(19)F NMR),UV-Vis spectroscopy,cyclic voltammetry(CV)and thermogravimetric analysis(TGA),respectively.The results show that BDT4F-RO exhibits strong absorption in 300—700 nm area in thin film,and the absorption onset is located at 690 nm.Compared with BDT-RO,the analogue without fluorine atoms,BDT4F-RO has a deeper HOMO energy level,which is beneficial to a higher open-circuit voltage(0.95 V)of the fabricated photovoltaic device.However,the photo-electron conversion efficiency of BDT4F-RO is generally inferior to that of BDT-RO,and this can be attributed to lo-wer miscibility of BDT4F-RO:IDIC blend that caused by fluorination.