Photovoltaic Properties Of Naphthalenothiophene Imide-based Polymer Donor

Due to advantages of easy fabrication,light weight and flexibility,Organic solar cells（OSCs）have attracted increasing attention.The power conversion efficiency（PCE）of OSCs has been greatly improved owing to the rapid development of the materials of active layer and the continuous optimization of devices.The appearance of high-performance non-fullerene electron acceptors,such as ITIC,Y6 and their derivatives,have broken the efficiency bottleneck of OSCs,achieving the highest PCE around 18%so far by using Y6 and its derivatives as acceptor.Polymer donor lags behind non-fullerene acceptor materials due to most donor materials designed to match with fullerene and their variants,which do not perfectly match with Y6 in absorption spectra,energy levels and miscibility.Thus far,only several polymer donors,such as PNTB series and D18exhibit a PCE higher than 17%.Therefore,it is critically important to design new conjugated polymer donors and systemically study the optimization conditions of new polymer donor based OPV devices.Here,my thesis focuses on OPV device fabrication and characterization based on naphthalenothiophene imide-based polymer donors.The achievements were shown as follows:1)Employing naphthalenothiophene imide-based polymer PNTB1 as electron donor and Y6as electron acceptor,the highest efficiency of 15.18%was obtained in the binary OPV device.Using IT-4F as electron acceptor,the non-halogenated solvent processing enable the highest PCE of 10.83%.The high efficiency and ease in synthesis of PNTB1 without introducing any F or Cl electron-deficient groups into conjugated backbone make PNTB1 a very promising polymer donor.Meanwhile,the GIWAXS result shows that the strong intermolecular interaction of polymer PNTB1 is unfavorable for phase separation optimization,pointing out the direction for the structure optimization of materials.2)Polymer PNTB and PNTB-2T were further developed.The solar cell devices for PNTB-2T:Y6 exhibit an efficiency of 16.72%,which is further enhanced to 17.35%by the third component PC₇₁BM,whereas that for PNTB:Y6 is only 3.81%.Importantly,PNTB-2T based devices exhibit excellent batch-to-batch reproducibility with large molecular weight variation,showing that PNTB-2T is one of the best polymer donors The photophysical properties and morphology characterizations revealed the reseaons why PNTB-2T is much better photovoltaic properties than that of PNTB.Furthermore,it was demonstrated that introduction of extra thiophenes between donor and acceptor units is a effective strategy to tune the film forming property of polymer donorsThrough photovoltaic study based on polymer donors of PNTB1,PNTB,PNTB-2T,remarkable achievements of device optimization based on NTI-based polymer donor have been obtained,which will enlighten the future development of polymer donors.