Preparation And Photovoltaic Performance Of Conjugated Polymers Based On Aromatic Fused Ring

Utilizing optoelectronic devices to convert solar energy into electricity is an important measure to solve energy crisis nowadays.Organic solar cells have become a hot area of research because of its good advantages such as easy to carry,low cost,flexibility.The latest reported power conversion efficiency of polymer solar cells has exceeded 13%.Under this favorable trend,it is our goal to design and synthesize polymer materials with broad absorption spectrum,high mobility and suitable energy levels.This paper focuses on the synthesis of three types of aromatic fused ring compounds.We will study the relationship between the molecular structure and the device properties by characterizing the optical and electrochemical properties of the materials and the photovoltaic properties in the bulk heterojunction solar cell devices,to provide new ideas for the future research work.This paper systematically describes the development of polymer solar cell devices,the working principle and the characterization of materials.Seven kinds of donor-acceptor(D-A)conjugated polymers with fused ring structure were synthesized through Stille polymerization.The main contents as follows:(1)Two kinds of polymers PBDTT-EH and PBDTT-EO with high planar structure were designed and synthesized with thiophene benzodithiophene(BDTT)as the donor material and TPD as the acceptor unit.polymers have the same backbone,but with different side chains,where PBDTT-EO has the longer branched 4-ethyoctyl side chains,and showed better solubility.Due to the large planarity of structures,two polymers showed good ?-? stacking effect;in the electrochemical test,according to the CV curve,we calculated different HOMO energy levels of two polymers,which was attributed to the different alkyl chain.In the photovoltaic performance of the device,the efficiency of the devices based on PBDTT-EH and PBDTT-EO were 1.92% and 2.86%,respectively.Indicating that the choice of alkyl side chains can change the degree of conjugation,which in turn affects device efficiency.(2)Two kinds of polymers PDTBT-Qx and PDFBT-Qx were synthesized by the combination of quinoxaline(Qx)unit with DTBT and fluorinated DFBT.The DTBT was replaced by different numbers of fluorine atoms to promote the formation of intramolecular hydrogen bonds and enhance the interaction between molecules.The solubility of the polymer was improved because of the longer 2-decyltetradecyl groups in quinoxaline units.And also Improved the planarity of polymer molecules.However,the efficiency of the fluorine-substituted polymer is relatively low,mainly due to the blue shift of the absorption spectrum.(3)We synthesized three polymers PQx-PT,PFQx-PT and PFFQx-PT,with fluorinated thiophene(PT)derivatives as the donor,quinoxaline derivatives as the receptor which contain different number of fluorine atoms.The "F-S molecular lock" effect of fluorinated thiophene is used to enhance the planarity and crystallinity of the polymer.with the increased number of fluorine atoms in the polymer,the optical band gap of the three polymers were 1.48 eV,1.57 eV and 1.66 eV,respectively.It is found that with the increase of F atoms,the optical bandgap decreases,which improves its power conversion efficiency.