Design,Synthesis And Photovoltaic Property Of Small Molecule Acceptor Materials Based On A-D-A Structure

Nowadays,the energy consumption is very huge making the fossil fuel resources decreased dramatically.In order to develop a new kind of energy resource,the clean,renewable solar energy has been attracted much attention.In order to make better use of solar energy,many types of solar cells have been investigated.Especially,the organic solar cells（OSC）with the advantages of low cost,light weight,and flexibility.In the past five years,the photoelectric conversion efficiency of organic solar cells was increased with the discovery of new organic donor molecules.In additional,exploration of new non-fullerene small molecule acceptor materials with A-D-A structure has become a research hotspot in the field of organic solar cells.In this thesis,four fused-ring non-fullerene molecules（IN-4F,ISI-4F,ISI-4Cl and TT-S-4F）with A-D-A structure were designed and synthesized,and their photovoltaic properties were studied in detail.1.The acceptor molecule IN-4F with an A-D-A structure was synthesized by fusion of 4,8-bis（tripropylsilylthiophene）benzo[1,2-b:4,5-b′]dithiophene（SiBDT）with thieno[2′,3′:4,5]thieno（TT）.The nine-membered fused-ring backbone was obtained by expanding theπ-system.In IN-4F,difluorodicyanoindandione（IC-2F）is the terminal group.IN-4F possesses an extendedπ-systems and silane-based side chains compared to IT-4F.As a result,IN-4F has higher LUMO energy level and narrower optical band gap than those of IT-4F.The IN-4F-based binary solar cell shows 13.0%PCE in which PM6 was used as the donor.A ternary solar cell with 14.9%PCE was obtained by addition of IN-4F to PM6:IT-4F system.In additional,V_occ and J_sc are also higher than that of binary solar cell.This is because the similar structure of IN-4F and IT-4F making the morphology of the film and theπ-πstacking patterns both well kept in the ternary solar cell.When IN-4F was added into the PM6:Y6 system to prepare a ternary solar cell,as a result,the V_oc was increased with the increasing of LUMO energy level and the J_sc was increased with the increasing of charge mobility.Moreover,the FF was intact.Therefore,an excellent 16.3%PCE was achieved.2.Two new A-D-A structural small molecule acceptors,ISI-4F and ISI-4Cl,were designed and synthesized by utilization of 4,8-bis（tripropylsilylethynyl）benzo[1,2-b:4,5-b′]dithiophene（ASiBDT）as the building block.The central conjugated unit of these two compounds was extended to nine benzene rings.Difluorodicyanoindandione（IC-2F）and dichlorodicyanoindanedione（IC-2Cl）are the terminal groups for ISI-4F and ISI-4Cl,respectively.Due to the extended conjugate structure,ISI-4F and ISI-4Cl exhibit a strong and broad absorption in the near infrared region.In additional,the planarity of the two molecules was enhanced by introducing tripropylsilylethynyl side chains.As a result,the higher molar absorption extinction coefficients were achieved than that of IN-4F.Two blend layers were prepared by using ISI-4F or ISI-4Cl as the acceptor and PM6 polymer as the donor.The layers possess fine phase separation morphology.Moreover,high and balanced charge carrier mobility was achieved.The binary solar cells,PM6:ISI-4F and PM6:ISI-4Cl,have 12.45%and 12.05%PCE,respectively.An excellent J_sc of 22.78/20.47 mA/cm² and a higher V_oc（0.88/0.87 eV）were achived in the two cells.3.An A-π-D-π-A-type nonfullerene acceptor named TT-S-4F was designed and synthesized based on indacenodithiophene（IDT）with a side chain of alkyl thiophenyl,in which3,6-dimethoxylthieno[3,2-b]thiophene and difluorodicyanoindandione（IC-2F）were used as theπ-bridge unit and the terminal group,respectively.TT-S-4F exhibits enhanced intramolecular charge transfer（ICT）because of the electron-withdrawing group IC-2F andπconjugated spacer unit.As a result,it possesses approximative optical band gap and higher lowest unoccupied molecular orbital（LUMO）level than those of IEICO-4F.A ternary solar cell with a 12.54%PCE was prepared by addition of TT-S-4F（10%wt）to the PTB7-Th:IEICO-4F system.Moreover,the J_sc,V_oc and FF of the ternary solar cell are higher than those of PTB7-Th:IEICO-4F-based binary solar cell.