Study On Synthesis Methods And Device Performance Of Asymmetric Organic Photovoltaic Donor Materials

In recent years,with the increasingly serious energy problem,organic solar cells have achieved rapid development.At present,the highest efficiency of a single organic solar cell reported in the literature has reached more than 19%.Compared with inorganic materials,it has the characteristics of flexibility,light weight and easy to prepare in large area.The performance of organic solar cells can be adjusted by tailoring the molecular structure of active layer materials.The most common method to achieve better control of material properties is to use different design strategies to synthesize organic semiconductor materials.Due to the diversity of structural modification of organic semiconductor materials,it is easy to change the structure on the main chain and side chain,improve the photoelectric properties and molecular stacking morphology of materials,and realize the preparation of efficient organic solar cell devices.However,most of the research focuses on small molecule acceptor materials,and the research on polymer donor materials is still lagging behind.In this paper,we selected benzodithiophene(BDT)and benzodithiophene-4,8-dione(BDD)units with good flatness,introduced symmetric and asymmetric π-bridge units between BDT and BDD units through bromination and Stille cross-coupling reaction,synthesized a series of new organic polymer donor materials.The main results are as follows:(1)By introducing different π-bridge units between BDT and BDD units,five new polymer donor materials were designed and synthesized,wherein P1,P2 and P3 are polymer donor materials based on asymmetric backbone,and P4 and P5 are polymer donor materials based on symmetric backbone.The test results show that the asymmetric backbone can affect the geometric configuration of the material,and increase the dihedral angle between BDT unit and conjugated main chain.This larger torsional geometric structure is conducive to improving the solubility of the material and inhibiting the strong aggregation of the corresponding polymer.At the same time,the asymmetric backbone can regulate the energy level and absorption spectrum of the material itself,which is conducive to light collection and charge transfer.(2)Organic solar cells were prepared by blending five kinds of polymer donor materials and small molecule acceptor Y6,and the influence of asymmetric backbone on photovoltaic performance of devices was investigated.Test results show that P1,P2 and P3 devices based on asymmetric backbone are superior to P4 and P5 devices with symmetric backbone in terms of carrier mobility,energy loss and exciton dissociation efficiency.Specifically,the devices based on P2:Y6 show the highest power conversion efficiency,reaching 16.22%.In addition,the analysis of morphology and molecular orientation found that the asymmetric backbone can regulate the crystallinity and molecular orientation,which provides a new idea for obtaining efficient polymer donor materials.