Study On Synthesis And Properties Of Novel Fluoro-Pyrazine Based Donor Materials

Organic solar cells(OSCs)have attracted widespread attention due to their advantages of solution processing,low cost,light weight,flexibility,transparency,and portability.In this dissertation,a series of novel photovoltaic donor materials based on pyrazines have been synthesized for the purpose of designing and developing high-efficiency polymer donor materials,and the influence of the molecular structure of the materials on the photovoltaic performance of the devices has been studied in detail.The photoelectric conversion efficiency of the device is improved by broadening the absorption spectrum of the polymer,adjusting the electrochemical energy level,and improving the device structure and interface modification.Focus on this,the contents of this study include the following three parts:1.The structure of pyrido[3,4-b]pyrazine(PP)has strong electron-withdrawing property and effective intermolecular ?-? interaction due to the existence of N atom and imine atom.In addition,more sites can be modified,and its solubility and bandgap can be well controlled.These features well meet the requirements of organic photovoltaic devices on the material structure.A novel fluoropyridine pyrazine(/PP)acceptor unit was designed and synthesized,and a Stille coupling reaction was performed with an alkthiothiophene-substituted benzodithiophene(BDT)tin compound to obtain a medium bandgap polymer,BDT-S-fPP,the polymer shows good solubility and thermal stability.We also investigated the photovoltaic performance of blend films of BDT-S-fPP and electron acceptor[6,6]-phenyl-C71-methylbutyrate(PC71BM).OSCs with a blend ratio of BDT-S-fPP:PC71BM(1:1,w/w,with 1.2 vol%DIO additive)as the active layer showed a PCE of 6.2%,with a open-circuit voltage(VOC)of 0.80 V,a fill factor(FF)of 56%and a short-circuit current density(JSC)of 13.85 mA cm-2.2.In order to investigate the influence of different numbers of F atoms in the acceptor units on donor-acceptor(D-A)type conjugated polymers on the photovoltaic performance of the material.We synthesized a series of D-A type two-dimensional conjugated polymers PT-PP,PT-2fPP,PT-4fPP.The photophysical properties,mobility,and morphology of the three polymers were further studied.The results show that the introduction of different numbers of F atoms on the phenyl ring of the PP side has a relatively small effect on its highest occupied molecular orbital(HOMO)level,however,the photovoltaic performance of these devices differs greatly.Different absorption spectra,charge mobility,and morphology lead to differences in the three photovoltaic properties.Among them,PT-4fPP-based organic photovoltaic devices(ITO/PEDOT:PSS/PT-4fPP:PC71BM(1:1,w/w)/ZrAcac/Al)showed the best photovoltaic performance when 0.5%DIO was added At the time,PCE reached 7.61%,which is the highest for PP-based PSCs with a single heterojunction structure.3.A new medium bandgap Qx copolymer,HFAQx-T,was synthesized and used as the donor polymer in OSCs.HFAQx-T showed good solubility in common organic solvents,a broad absorption from 300 to 700 nm,a low-lying HOMO energy level of-5.50 eV.The optimized conventional single-junction device of HFAQx-T:PC71BM achieved a PCE of 9.2%,with a VOC of 0.9 V,a JSC of 14.0 mA cm-2 and a FF of 0.74,which is the highest efficiency reported in the literatures to date for BDT-Qx based fullerene OSCs.When blended with ITIC,the HFAQx-T-based device showed a PCE of 9.6%,attributing to the more complementary absorption and better energy level match of the HFAQx-T and ITIC.HFAQx-T is among a few D-A copolymers that can deliver>9%efficiency in both fullerene and nonfullerene solar cells,which is inspiring for the design of new donors compatible with fullerene and fullerene-free acceptors.The results indicated that incorporation of two weak electron-donating alkyl side chain onto the 4-positions of the phenyl at the Qx unit by side chain engineering would be a feasible approach to improve photovoltaic properties.