Synthesis And Photovoltaic Performance Investigation Of Polymer Donor Materials Based On Benzodithiophene Conjugated Backbone

Energy is one of the important factors restricting the survival and development of human beings.On the one hand,traditional petrochemical energy sources are facing the crisis of energy depletion,and on the other hand,they also cause great pollution to the environment at the same time.Therefore,human beings must develop and use some resource-rich,renewable and environmentally friendly new energy sources to replace petrochemical energy.Reduce pollution to the environment while slowing down the crisis of traditional petrochemical energy depletion.Among the many renewable energy sources,solar energy is an ideal resource-rich renewable clean energy source.How to use solar energy more efficiently has become one of the hot research topics around the world.Organic solar cells are a device that converts light energy into electrical energy through chemical materials.Due to their unique advantages such as light weight,flexibility,and solution processing,organic solar cells have attracted widespread attention from academics and industry.The power conversion efficiency（PCE）is the most important parameter for measuring the performance of organic solar cells.After decades of development,the PCE of organic solar cells has broken through to 18%,and it has reached the dawn of industrialization.Designing and synthesizing new high-performance organic photovoltaic materials is one of the main ways to further improve the PCE.Therefore,the structure-activity relationship between the molecular structure of organic photovoltaic materials and the performance of photovoltaic devices is one of the research hotspots in this field.Organic photovoltaic materials are divided into electron donors and electron acceptors according to their ability to donate or receive electrons.This thesis focuses on some researches on electron donors.The first part of the work is to design and synthesize two kinds of polymer donor materials with different lengths of ester groups.The second part of the work is to synthesize two symmetrical and asymmetric chlorine-substituted polymer donor materials by introducing chlorine atoms at different positions of the high-performance polymer donor material PBDB-T.Investigated the effects of the symmetry of the chlorine atom position on the molecular structure of such polymer donor materials and the photovoltaic performance of corresponding devices.The specific research content is as follows:Conjugated polymers（P3TE-C8 and P3TE-C12）with two different side chains based on thienyl-substituted benzodithiophene and dicarboxylic ester terthiophene were synthesized and applied in non-fullerene polymer solar cells（PSCs）.Detailed studies revealed that the length of side chains in conjugated polymers showed a weak influence on their optical bandgaps and electrochemical properties,but a strong influence on their aggregation behaviors in solution,films,bulk heterojunction morphologies and photovoltaic performances.Among PSC devices,the P3TE-C8:ITIC-based device showed a PCE of 5.49%,a V_oc of 0.814 V,J_sc of 12.86 mA cm^-2 and FF of 52.48%,while the P3TE-C12:ITIC-based device exhibited a higher PCE of 7.64%,with simultaneously improved photovoltaic parameters of V_oc of 0.906 V,J_sc of 14.20 mA cm^-2 and FF of 59.36%.This work demonstrates that the reduction aggregation in conjugated polymers via changing the length of side chains is an effective method to improve PSC performancesTwo conjugated donor polymers（PB2F-Cl and PB2F-2Cl）based on benzodithiophene and benzodithiophene-4,8-dione with asymmetrical and symmetrical chlorinated thiophene-bridges were designed and synthesized.Both polymers exhibited extremely deep HOMO levels of-5.50 and-5.56 eV for PB2F-Cl and PB2F-2Cl,respectively.Although the PB2F-Cl had a more planar conjugated backbone,PB2F-Cl exhibited weaker aggregation behaviour than that of PB2F-2Cl in chlorobenzene solution due to its regioirregular conjugated backbone.After blending with IT-4F acceptor,PB2F-Cl:IT4F film exhibited slightly stronger lamellar stacking and weakerπstacking compared to PB2F-2Cl:IT-4F film as confirmed by grazing-incidence wide-angle X-ray scattering（GIWAXS）measurements.In PSCs,the power conversion efficiency（PCE）of PB2F-Cl:IT-4F-based PSC was 10.81%,while the PCE of PB2F-2Cl:IT-4F-based PSC reached 12.79%.