Synthesis And Characterization Of Thiopyrrole Fused Ring Non Fullerene Electron Acceptor Materials

Due to the advantages such as the better light response and easily adjustable energy level of non-fullerene acceptors(NFAs),as well as the low photoexciton splitting energy and energy disorder in organic / polymer solar cells(OSCs)devices based on NFAs,the power conversion efficiency(PCE)of NFAs-OSCs with NFAs as electron acceptor material has been boosted up to 18.6%-22.02%.However,the PCE and stability of the OSCs should be improved for practical applications.In spite that the PCE of the APCSs,in which both electron donor and acceptors in the devices are polymers,is lower than those for the OSCs from polymers paired with fullerene or non-fullerene acceptors,they have still received great attentions due to their unique characteriscts in the achievement of the flexible and stretchable device with remarkable stability.In this paper,four kinds of electron acceptor conjugated polymers,which wereprepared by Stille coupling reaction of brominated derivative of non fullere ne acceptor Y6 with long side chains and the aromatic units like of 3,3’-difluo-ro-2,2’-dithiophene,3,4-difluorothiophene and 3,4-ethylenedioxy-thiophene as π-spacer.Besides these,the absorption,electrochemical,photostability and aggrega tion behaviors,as well as the application of them as electron acceptor for APS Cs,have been preliminarily investigated.In chapter 2,two acceptor polymers with name of PYI-DFs and PYO-DFs,are designed and developed.Both polymers exhibit extensive absorption ranging from400-900 nm,with the maximum absorption peaks in the films are 785 nm and 720 nm respectively.The lowest unoccupied molecular orbital(LUMO)and highest occupied molecular orbital(HOMO)energy levels of the PYI-DFs and PYO-DFs,are determined to be-4.23 e V and-4.17 e V,-5.61 and-5.60 e V,respectively.Contributed to narrower band gap,higher extinction coefficient and shorter inter chain distance of the PYI-DFs in contract with PYO-DFs,the APSCs with PYI-DFs as acceptors,presented higher PCE of 11.6% vs 9.19% for the devices with PYO-DFs as acceptors.In Chapter 3,the acceptor polymer PYO-2Fs was constructed with 3,4-difl-uorothiophene as electron rich unit and 3-dinitroylmethylene-6-bromoindanone a s electron deficient unit.At the same time,it was compared with the acceptor polymer PY-OT without f protons in the donor unit.,the absorption spectrum of PYO-2Fs has a slight blue shift,but there is little difference.The LUMO levels of PYO-2Fs and PY-OT are-4.51 e V and-3.90 e V respectively.The in troduction of F atom has a certain effect on the regulation of LUMO level.At the same time,PYO-2Fs showed appropriate stacking behavior and good phot ostability.Taking PM6 as the donor,the PCE of the device based on PM6/PY O-2Fs is 3.45%.Compared with PY-OT,the efficiency of PYO-2Fs is not sati sfactory.The reason is that although the introduction of F atom can effectively improve its light absorption ability and regulate the energy level of polymer,too low LUMO energy level may not be conducive to obtaining higher open c ircuit voltage,thus affecting the performance of devices.In Chapter 4,the polymer PYI-EDOT was constructed with EDOT with strong electron donor ability as electron rich unit and Y-I-20-Br as electron deficient unit.The polymer showed strong and wide absorption in the range of 400-800 nm.Compared with the polymer PY-IT,the absorption light of PYI-EDOT showed obvious blue shift.The introduction of strong electron donor units makes PYI-EDOT have stronger light absorption ability.The HOMO and LUMO levels of PYI-EDOT are-4.13 e V and-5.63 e V respectively.The photovoltaic device based on PM6 /PYI-EDOT realizes an open circuit voltage of 0.787 V and PCE of 0.69%.In general,although the photovoltaic performance of polymers for electron donor units is not satisfactory,EDOT provides new ideas and strategies for the design and development of receptors with better performance.