Synthesis And Properties Of Organic Photovoltaic Materials Based On C₆₀ Derivatives

In recent years,with the rapid development of economy,science and technology,the expansion and the diversification of human activities are becoming more and more extensive and energy consumption is also increasing,which resulted in various issues of environment and energy,of course,these issues have become increasingly prominent.Solar energy has become one of the most promising new energy sources because of its large reserves,wide distribution,clean and non-pollution,renewable and other advantages,and it has the great potential to replace traditional energy and has attracted a lot of attention in the world.The silicon-based inorganic solar cells can be commercialized and comprehensive application in the daily life,but it's fatal shortcomings,such as high cost,heavy weight,silicon resource shortage,serious environmental pollution and high energy consumption for the production and purification of silicon materials,limited the further research and application.Recently,organic/polymer thin film solar cells have attracted much attention due to their advantages such as low cost,light weight,simple fabrication process and flexible devices,Among them,bulk heterojunction(BHJ)polymer solar cells(PSCs)have been widely studied because of their advantages such as increasing the effective separation of the excitons and charge transport at the D/A interface.From the perspective of the active layer material,there are many studies on the electron donor materials and some results have also been achieved,but the receptor materials have not been given much attention.Actually,the electron acceptor material also play a very important role in the high-performance PSCs.Therefore,we focused on the synthesis of fullerene derivatives and non-fullerene small molecule acceptor materials with broad and strong absorption in the visible region and better compatibility with P3 HT level in this thesis.The specific research content can be divided into the following three parts:In the first part,the novel fullerene derivatives Cz-C60 and Cz-2C60 with good solubility can be synthesized.Because of the strong electron donating ability of carbazole group,the LUMO levels of Cz-C60 and Cz-2C60 were increased by 0.05 eV and 0.04 eV compared with the LUMO level of PC60 BM,respectively.And it is for the reason that C60 is a good electron acceptor material,so the target compound Cz-2C60 grafted two C60 moieties has wide and strong UV-Vis absorption,higher the LUMO level and the electron transport capacity.Cz-C60 and Cz-2C60 were investigated in terms of UV-Vis absorption,cyclic voltammetry,thermogravimetric(TG),morphology and photovoltaic properties.When the mass ratio of the P3 HT regarded as the donor material and PC60 BM,Cz-C60,Cz-2C60 regarded as the receptor materials is 1:0.75,the PCE of P3HT/PC60 BM regarded as active layer is 3.71%,the PCE of P3HT/Cz-C60 regarded as active layer is 3.59% and the PCE of P3HT/Cz-2C60 regarded as active layer is 3.88%.In the second part,we continues to focus on the problems of poor solubility,weak absorption in the visible area and poor matching of the energy level for the fullerene derivative acceptor materials.Of course,FST-C60,bis-FST-C60(double addition fullerene derivative),FTT-C60 and FFT-C60 grafted fluorenone with electron-donating ability and thiophene rings with-C8H17 with strong absorption ability have been successfully synthesized.The absorption spectra of FST-C60 and PC60 BM is not significantly changed,however,the absorption peak position of bis-FST-C60 is different from that of the traditional acceptor material PC60 BM,and it has no obvious sharp absorption peak.FTT-C60 and FFT-C60 have a strong characteristic absorption peak at 335 nm and 334 nm,respectively,and the two compounds respectively have no sharp absorption peak in the range of 360 ~ 465 nm and 360 ~ 500 nm,but their absorption intensity is stronger than PC60 BM.And the LUMO levels of FST-C60,bis-FST-C60,FTT-C60 and FFT-C60 are-3.89 eV,-3.68 eV,-3.77 eV and-3.72 eV,which is increased respectively by 0.04 eV,0.25 eV,0.16 eV and 0.21 eV compared with the LUMO level of PC60BM(-3.93 eV),respectively.According to the thermogravimetric analysis,and the thermal stability of FST-C60,bis-FST-C60 and FTT-C60 is poorer than that of PC60 BM,but the thermal stability of FFT-C60 is better than that of PC60 BM.In the third part,the non-fullerene small molecule acceptor materials have attracted much attention because of their simple synthesis,good matching of energy level,low cost,good solubility in common solvents,strong absorption in the visible region and other characteristics.In this chapter,we find new synthetic methods for STBF,TTBF and FTBF to obtain finally the three target compounds in high yield.The maximum absorption peaks of STBF,TTBF and FTBF in dichloromethane solution are located at 465 nm,381 nm and 408 nm,respectively,and the LUMO levels of STBF,TTBF and FTBF is-3.27 eV,-2.86 eV and-2.61 eV,respectively,which are increased respectively by 0.64 eV,1.05 eV and 1.3 eV compared with the LUMO level of PC60BM(measured by-3.91 eV in the second chapter).TTBF has a good thermal stability,and it began a significant decomposition from 335 °C and sharply decomposed until TTBF completely decomposed at 515 °C,finally,the compound lost 56% of weight.