Design,Synthesis And Properties Of Imide Non-Conjugated Polymer Zwitterionic Cathode Interlayer Materials

During the development of organic solar cells（OSCs）,interfacial engineering has become the focus of researchers because of its abilities of reducing the transport barrier between the active layers and the electrodes and passivating interfacial defects.The power conversion efficiency（PCE）of single-junction OSCs has approached 20%with the rapid development of fused-ring electron acceptors（FREAs）.There are no free ions in the structure of polymer zwitterions,thus the instability of devices caused by the migration of counter-ions under electric field is avoided.Meanwhile,there are no reactive amine groups in the structure,which can avoid chemical reaction between the amine groups and non-fullerene acceptors.Compared with conjugated polymer zwitterions,the synthesis of non-conjugated polymer zwitterions does not require metal catalysts,which is green and environmentally friendly,and the reaction conditions are mild.Furthermore,the study of non-conjugated polymer zwitterions as cathode interlayers（CILs）for OSCs has been rarely reported and there are many problems and challenges.In this thesis,two types of non-conjugated polymer zwitterionic cathode interlayers systems were obtained by introducing the n-type conjugated units of imide into the backbone of polymer.The main work is as follows:1.The non-conjugated polymer zwitterion PDI-NPZ was designed and synthesized.Compared with the classical small-molecule zwitterion PDI-Z,PDI-NPZ exhibited better film formation,higher conductivity and more suitable energy levels.In the classical non-fullerenes active layer system of PM6:Y6,the devices using PDI-NPZ as CIL reached the highest PCE value of17.72%,which was significantly higher than that of PDI-Z modified devices.The influence of the interlayer thickness on the PCE value was investigated and 91%of the highest PCE value was still maintained when the film thickness of PDI-NPZ reached to 35 nm.Moreover,the high performance non-fullerene system OSCs based on PM6:BTP-eC9 achieved a maximum PCE value of 18.34%.These results demonstrate the validity of the design strategy for polymerization of small-molecule zwitterions.2.D-A type non-conjugated polymer zwitterions,PDEN-PDISB and PDEN-NDISB,were designed and synthesized.They were found to have excellent solubility,good film-forming ability and efficient interfacial self-doping property,where the self-doping properties further facilitate the electron transport and extraction in the devices.In the classical non-fullerenes active layer system of PM6:Y6,PCE values as high as 17.62%and 17.85%were achieved for PDEN-NDISB and PDEN-PDISB,respectively.For PDEN-PDISB,high PCE values can still be achieved in the thickness range from 6 nm to 30 nm.In the high performance binary and ternary systems of PM6:BTP-eC9 and PM6:BTP-eC9:PC₇₁BM,the maximum PCE values of18.43%and 18.85%were achieved,respectively.All the results demonstrate the generalizability of PDEN-PDISB as CIL in OSCs.