Design And Photovoltaic Performances Of Low-bandgap Nonfullerene Acceptors Through Modifications Of The Main Chain And Side Chain

In recent years,many countries have paid more and more attention to the development of renewable energy,aiming to solve the energy crisis and global warming.Solar energy,as a widely distributed clean energy,is one of the most competitive renewable energy.Organic solar cells?OSCs?,as the third generation of new photovoltaic devices,have the advantages of light weight,solution processing,and large-area printing.With the optimization of active layer materials and device structure,the performances of organic solar cells have been continuously improved,showing a broad application prospect.Active layer materials play an important role in organic solar cells.In recent years,the development of nonfullerene acceptors?NFAs?has been particularly rapid,which has made great contributions to the energy conversion efficiency of OSCs.In Chapter 1,A-D-A type acceptors were reviewed.The universal material design method was summarized according to the design of the electron-donating unit,side chain,bridge unit and electron-withdrawing unit.We designed and synthesized a series of low-bandgap acceptors through modification of the main chain and side chain.And we systematically investigated the effects of molecular structure on the optical,electrochemical and photovoltaic properties of materials.In Chapter 2,we introduced siloxane-terminated side chain and 2-ethylhexyl side chain into the NFAs,and synthesized two small molecules,Si-IEICO4F and EH-IEICO4F,with ultra-narrow bandgaps.Due to the flexible side chain,the energy levels of two acceptors were elevated,resulting in the narrowed the bandgaps.The PCE of two OSC devices based on PTB7-Th:Si-IEICO4F and PTB7-Th:EH-IEICO4F were 10.31%and 7.88%,respectively.The Si-IEICO4F-based device performed better,owing to the siloxane-terminated side chain yielding tighter molecular packing and better morphology of the blend film.In Chapter 3,three main chain twisted low-bandgap acceptors,i-IEOF,i-IEOS,and i-IEOFS,using 2F-IC and CPTCN as electron-withdrawing units,were synthesized.The twisted backbone can increase the bandgaps of molecules.With the introduction of 2F-IC,the LUMO level was down-shifted.With wide-bandgap PBZ-C7Si as polymer donors,the PCE of i-IEOS-and i-IEOFS-based OSC devices were 6.85%and 9.68%,respectively.While the device based on i-IEOF showed excellent photovoltaic performance with a high PCE of 14.54%,due to the higher J_SC(24.46 m A cm^-2)and FF?68.32%?.In Chapter 4,p-azaquinodimethane?p-AQM?was introduced into NFAs for the first time,and synthesized two narrow-bandgap acceptors AQMIC and AQMOIC.Quinoidal structure endued NFAs with narrow-bandgap,good planarity and crystallinity.Blending PTB7-Th as polymer donors in the OSC devices,the PCE of AQMIC-and AQMOIC-based devices were1.45%and 0.38%,respectively.Their J_SC values were extremely low,resulting from very large phase separation in blend films.