Synthesis Of Conjugated Polymers Based On Benzodithiophene/Furan Units For Solar Cells And Photocatalytic Water Hydrogen Production

In recent years,environmental problems such as global warming and frequent occurrence of extreme climates have become prominent.In the final analysis,it is caused by the continuous consumption of fossil energy such as oil and coal.Therefore,the development and utilization of new sustainable clean energy is extremely urgent.Converting solar energy into electric energy or using solar energy to photolyse water to produce hydrogen is one of the ways to effectively solve energy shortage and environmental problems.Organic conjugated polymers have the advantages of strong structural modification,easy adjustment of chemical energy levels,and simple synthesis and preparation.It is widely used in photoelectric conversion,photocatalytic water hydrogen production and other fields.In this paper,the unit structure of benzodithiophene and benzodifuran with better planarity is selected as the research object.Through Stille coupling reaction and Suzuki coupling reaction,a series of new organic conjugated polymers based on benzodithiophene and benzodifuran were designed and synthesized.By means of side chain modification,heteroatom substitution,and main chain conjugation length of polymer materials,systematically study its photoelectric conversion efficiency and photocatalytic hydrogen production performance,and explore the structure-activity relationship between the structure of conjugated polymer and its performance.(1)Designed and synthesized a series of new D-A type near-infrared conjugated polymer based on benzodifuran structure as donor unit,benzothiadiazolquinoxaline structure as acceptor unit,and side chain thiophene as bridge bond.Mainly systematically studied the effects of different side chain groups on the optical properties,electrochemical properties,thermal properties of the polymer and the performance of solar cell devices.This series of polymers have broad absorption in the range of 400nm-1200 nm,and the optical band gap is between 1.06 e V-1.12 e V.This type of polymer has very good thermodynamic stability,and the 5%weight loss temperature is above350?.However,the photoelectric efficiency of this series of polymers is low,the highest efficiency is only 0.56%,the main reason is that the electron withdrawing ability of benzothiadiazoloquinoxaline is too strong,and the HOMO energy level of the polymer is too shallow to form effective charge separation,resulting in low device efficiency.It provides a certain reference for the design of near-infrared organic solar cell materials.(2)Designed and synthesized two new organic conjugated microporous polymers PBDFSO and PBDTSO based on the copolymerization of benzodifuran and benzodithiophene derivatives with dibenzothiophene sulfone.Using the small radius of oxygen atoms and stronger electronegativity than sulfur atoms,the influence of heteroatom substitution on the optical properties,electrochemical properties and photocatalytic hydrogen production performance of polymers was systematically studied.Studies have shown that the highly electronegative oxygen atoms can promote the red shift of the optical absorption of the microporous conjugated polymer.And the thermodynamic properties of these two polymers are very stable,and the decomposition temperature of 5%thermal weight loss is above 430?.When studying the performance of photocatalytic hydrogen production,we found that when ascorbic acid at a concentration of 0.2 mol/L was used as a sacrificial agent without a co-catalyst,the photocatalytic hydrogen production rate of polymers PBDFSO and PBDTSO reached1699?mol·h^-1·g^-1 and 1973?mol·h^-1·g^-1.(3)Thienothiophene and benzodithiophene units with different conjugation lengths as donor units,respectively copolymerized with bithiophene units with oligoethylene glycol side chains to obtain new D-A type organic linear polymers PDTOEGTT and PDTOEGBDT.Systematic study of the effect of conjugated framework length on the optical properties,electrochemical properties,band gap energy level,and photocatalytic hydrogen production performance of linear polymers.Through experimental tests,it is found that these two polymers have good absorption in visible light,and can meet the requirements of photocatalytic hydrogen production.When the concentration of 20%triethanolamine aqueous solution is a sacrificial agent without a co-catalyst,the photocatalytic hydrogen production rates of the polymers PDTOEGTT and PDTOEGBDT are 47.0?mol·h^-1·g^-1 and 46.6?mol·h^-1·g^-1.