Synthesis And Properties Of Organic Photovoltaic Materials Based On Carbazole-diketopyrrolopyrrole

Organic small molecular solar cells,using as a renewable energy carrier,possesses many advantages that is irreplaceable.Thus,it has drawn extensive attention in recent years.The efficiency of single junge organic small molecular device has been exceeded 11%,which marks the researches about organic small molecular solar cells have obtained some achievements.In this study,carbazole was used as an electron donor unit,diketopyrrolopyrrole was used as an electron acceptor unit and the electron-withdrawing group of 4-fluorophenyl,4-cyanophenyl the electron-donating group of 4-methoxyphenyl were used as the ending groups to assemble four D-?-A type asymmetric small molecules as donor materials.Moreover,PC₆₁BM was used as acceptor materials and bulk heterojunction was adopted as the structure for fabrication of solar cells devices.The synthesized molecules were characterized by ¹H-NMR,¹³C-NMR and MALDI-TOF HRMS.On this basis,the methods of thermogravimetric-analysis and fluorescence quenching were employed to prove that it was probable for the synthesized molecules to fabricate bulk heterojunction devices with PC₆₁BM.Then theoretical calculation was carried out to examine the energy levels and electronic-density distribution theoretically.The optical and electrochemical properties of the synthesized molecules were studied in depth by the methods of UV-visible absorptopn,cyclic voltammetry and fluorescence emission.Finally,the synthesized molecules were used to fabricate photovoltaic devices with PC₆₁BM.The results demonstrates that the introduction of terminal substituents has changed the energy level and electronic-density distribution of molecules,which has great influence on the optical,electrochemical and photovoltaic properties of synthesized molecules.Among them,CZBTDPPF and CZBTDPPO showed relatively good photovoltaic properties,the PCE of 1.97%and 1.91%were obtained respectively,and further device optimization can be carried out in the later study.The introduction of carbazole unit reduces the HOMO energy level of donor molecules,and the relative high Voc were obtained.The solubility of molecules can be improved by the introduction of alkyl chain,however,the planar properties of molecules can also be destroyed.Therefore,comprehensive consideration should be taken in the molecular design.A series of experiments were carried out in this paper to provide a reference basis for the subsequent studies of organic small molecule batteries based on carbazole and diketopyrrolopyrrole as basic units.