Synthesis And Photovoltaic Properties Of Halogenated Benzothiadiazole And Benzotriazole

Economic development is inseparable from the demand for energy.As a kind of clean energy,solar energy has attracted widespread attention from researchers.At present,the most widely used are monocrystalline silicon and inorganic semiconductor solar cells,while organic solar cells are used less.In recent years,the most studied are D-A polymer and A-D-A small molecule as donor materials,PCBM fullerene derivatives as receptors,and the current efficiency of organic cells based on fullerenes has exceeded 13%.In the past two years,due to the good stability of non-fullerene materials,photophysical properties,easy adjust energy levels and other advantages have attracted widespread attention.Among them,the introduction of strong electron-withdrawing is an effective way to improve the efficiency of organic solar cells,such as F or Cl.Therefore,we synthesized a series of fluorinated and chlorinated D-A polymers,fluorinated A-D-A small molecules and fluorinated non-fullerene acceptors,and systematically studied these materials.（1）Three A-D-A small molecules were designd and synthesized used2,6-Bis（trimethytin）-4,8-dioctyloxybenzo[1,2-b:3,4-b’]dithiophene as an electron donor,and benzo[d][1,2,3]triazole as electron-withdrawing.The effect of different amounts of fluorine atoms on the photovoltaic performance of organic small molecule solar cells was investigated by introducing different amounts of fluorine atoms into the acceptor.It has been found that the introduction of fluorine atom into the acceptor caused SM-2F and SM-4F to exhibit a significant shoulder peak,since the introduction of a fluorine atom enhances the intermolecular interactions,which facilitate charge transport.At the same time,the HOMO energy levels of SM-2F and SM-4F are reduced and their charge mobility is improved.Among them,SM-2F:PC₇₁BM has the best device performance,showing 3.94%energy conversion efficiency.（2）FiveD-Apolymersweredesigndandsynthesizedused2,6-Bis（trimethytin）-4,8-dioctyloxybenzo[1,2-b:3,4-b’]-dithiophene as an electron donor,benzothiadiazole as acceptor.Introducing different amounts of chlorine and fluorine atoms into the acceptor and the effects of different amounts of chlorine and fluorine atoms on the energy conversion efficiency of polymer solar cells were investigated by UV-visible absorption spectra,cyclic voltammetry,photovoltaic properties,charge transport and AFM.Finally,P2 has the best device performance,showing 3.97%energy conversion efficiency.（3）Two non-fullerene acceptors were designd and synthesized used（4,4,9,9-Tetrakis（4-hexylphenyl）-4,9-di）]hydro-s-indaceno[1,2-b:5,6-b’]dithiophene-2,7-diyl)bis（trimethylstannane）as electron donor and benzothiadiazole as acceptor.The fluorine atom was introduced into the benzothiadiazole to investigate the effect of fluorination on the performance of the non-fullerene organic solar cell.After a series of characterizations,it was found that these two non-fullerene acceptors showed relatively strong absorption in visible light,and after the introduction of fluorine atoms,the HOMO and LUMO of non-fullerene were reduced.Furthermore,The J_scc and V_oc have also been improved,and the energy conversion efficiency has increased from 2.5%to 3.22%.