Design,Synthesis And Characterization Of Unfused-Ring Acceptors For Organic Solar Cells

Organic solar cells have made tremendous progress in recent years.With the development of non-fullerene acceptor materials,the power conversion efficiency of organic solar cells based on non-fullerene small molecule acceptors has reached 19%.However,the research on organic solar cells still suffers from some problems,such as complicated synthesis and poor device stability.In this thesis,we designed and synthesized a series of unfused-ring non-fullerene acceptors,and applied them in organic solar cells.Then we investigated the relationship between the molecular structure of the acceptor and their device performance.In chapter 1,a detailed review is given on the recent progress of organic solar cells,including the working mechanism and characterization of the organic solar cell devices,representative polymer and small molecular donors and acceptors.In chapter 2,we synthesized a series of A-D-?-D-A unfused-ring acceptors,named 2,3BQ-ICF,2,5BQ-ICF,3,6DQ-ICF and 4,6MD-ICF,which utilize pyrazine(BQ),pyridazine(DQ)and pyrimidine(MD)as central core units,cyclopenta[2,1-b:3,4-b']dithiophen(CPDT)as the donor unit,and IC-2F as the terminal group.We fabricated organic solar cells with PM6 as the donor material and four molecules as the acceptor materials,respectively.Due to the planar molecular configuration and red-shifted absorption of 2,5BQ-ICF,the device based on PM6:2,5BQ-ICF obtained a power conversion efficiency(PCE)of 6.28%,which is the highest value in this series of acceptors.In chapter 3,we synthesized a series of A₁-D-A₂-D-A₁ unfused-ring acceptors named BDTC-F and BDTC-Cl,in which CPDT was employed as the D unit,while benzo[1,2-c:4,5-c']dithiophene-4,8-dione was employed as A₂ unit.To fine-tuning the absorption range and packing behaviors of the acceptors,IC-2F and IC-2Cl were incorporated in BDTC-F and BDTC-Cl,respectively.With the introduction of the electron-withdrawing group BDD,both acceptors show low energy levels,and the non-covalent intermolecular interactions between CPDT and BDD makes the molecules to show an almost flat molecular configuration.When blending with polymer donor PM6,devices based on both two acceptors exhibited PCE over 10%,low energy loss and excellent air stability.In chapter 4,we synthesized a series of A₁-D-A₂-D-A₁ unfused-ring acceptors named TBDD-F and TBDD-Cl,in which thiophene was employed between CPDT and BDD as?bridge.With the introduction of thiophene,TBDD-F and TBDD-Cl share a backflip configuration than BTDC series acceptors.At the same time,the LUMO and HOMO energy levels of the TBDD series acceptors are raised simultaneously,while the absorption and band gaps are almost unchanged.TBDD-F and TBDD-Cl share a planar molecular configuration,which is favorable for charge transfer.The devices based on J52:TBDD-F and J52:TBDD-Cl demonstrate PCE of6.46%and 5.36%,respectively.In chapter 5,we designed and synthesized two unfused-ring acceptors named TT-BDD-F and TT-BDD-Cl with thieno[3,2-b]thiophene(TT)as donor unit.Replacing the CPDT group with an alkoxy-substituted TT can obtain the acceptors with low-laying HOMO energy level while the LUMO energy level is basically unchanged,which proves the feasibility of adjusting the HOMO energy level of the molecule through the skeleton modulation.The weak electron donating ability of alkoxy TT reduced the intramolecular D-A interaction,which leads to blue shifted absorption of TT-BDD series.When blending with PM6,Both TT-BDD-F and TT-BDD-Cl based devices afford V_OCaround 1V.When introducing TT-BDD-F as third component in PM6:Y6 system to fabricate ternary OSCs.With the increased V_ocand J_sc,PM6:Y6:TT-BDD-F based devices reached highest PCE of 15.36%,which is higher than that of PM6:Y6 based binary OSCs.