Design, Synthesis Of Small Molecules Based On IDT And Application In Organic Solar Cells

In this paper, we have designed and synthesized a series of new narrow band-gap organic small molecules donor materials and applied to organic solar cells, the main work contains two parts:In the first part, we design and synthesize a series of linear D1-A-spacer-D2-spacer-A-D1 tetrafluorine substituted small-molecules with the same electron-rich core IDT, two difluorobenzothiadiazoles as electron-deficient unit and two n-hexyl-substituted bithiophenes as end groups with different π-conjugated spacer between A unit and D1 unit. We found that those devices based on BIT4 FTh, BIT4 FSe, and BIT4 FTT exhibited much higher Jsc than those based on BIT4 FFu and BIT4 FDT, which can be attributed to their straight conformation, relatively lower bandgaps and better film morphology. Notably, the devices based on BIT4 FTh showed an outstanding PCE of ca. 8.5%, with Voc = 0.90 V, Jsc = 12.70 mA cm-2, FF = 0.75, which is the highest PCE of solution-processed BHJ solar cells from difluorobenzothiadiazole-based small-molecules reported to date. Moreover, BIT4 FSe exhibit a PCE of 8.2% as well. The results indicated that combination the rational backbone geometry modulation from zigzag to straight conformation by altering π bridges and solvent vapor annealing to enhance the intermolecular interactions is an effective method to achieve high device performance.In the second part, we have synthesized a series of donor-accepor type small molecules donor materials based on D2-A-D1-A-D1-A-D2 linear frameworks. They both have the same electron-rich core IDT, and two difluorobenzothiadiazoles as electron-deficient unit and two n-hexyl-substituted bithiophenes as end groups with thiophene, selenophene spacer between A unit and D1 unit. Through investigate the photophysical properties, electrochemical properties, the HOMO/LUMO energy level and photovoltaic properties to study the impact of moiety sequence in the chemical structure of small molecular, especially for isomeric compounds on their basic properties and photovoltaic performance. The devices based on BIT6 FThSe and PC71 BM showed an PCE of 6.5 % after annealing treatment, while the devices based on BIT6 FSeTh which change moiety sequence showed an outstanding PCE of 8.4%. In shortly, our work has successfully shown that the high performance organic solar cells can be achieved by changing moiety sequence in t he chemical structure.