| Organic solar cells have attracted attention in academia and industry because of their advantages of low cost and flexible fabrication.The improvement power conversion efficiency（PCE）of organic solar cells mainly benefits from the continuous development of high-performance donor and acceptor materials.Indacenodithiophene and benzodithiophene have good planarity and high carrier mobility.Therefore,it is widely applied in the field of photoelectric materials.In this paper,a series of polymer donor materials and acceptor materials based on indacenodithiophene and benzodithiophene were designed and synthesized,and applied to organic solar cells to study the relationship between molecular structure and performance,so as to further improve the efficiency of organic solar cells.The specific research works are as follows:1.Two polymer acceptors PSF-IDIC and PSi-IDIC were developed by copolymerization of 2,20-（（2Z,20Z）-（（4,4,9,9-tetrahexadecyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b’]Dithiophene-2,7-diyl）bis（methanylylidene））bis（3-oxo-2,3-dihydro-1H-indene-2,1-diylidene））dimalononitrile（IDIC-C16）block with sulfur and fluorine functionalized benzodithiophene（BDT）unit and silicon atom functionalized BDT unit,respectively.The polymer acceptor PSF-IDIC and PSi-IDIC both show strong light absorption.The energy levels of PSF-IDIC and PSi-IDIC also match well with the current high-efficiency donor of PM6.PM6:PSi-IDIC based device obtained a PCE of 8.29%,PM6:PSi-IDIC based device obtained a PCE of 10.18%.PM6:PSF-IDIC devices have superior performance due to higher exciton dissociation,efficient charge transport,suppressed charge recombination and the optimize active layer morphology.These results suggest that optimizing side-chain functional atoms provides an effective strategy for developing high-performance polymer acceptors.These results indicate that the device performance can be regulated by copolymerization of benzodithiophene units modified with different functional atomic groups.2.Two polymer acceptors PCl-Si and PCl were continue developed by copolymerization of IDIC-C16 with chlorine and silicon functionalized BDT unit and chlorine atom functionalized BDT unit,respectively.The results show that PM6:PCl-Si based device obtained a PCE of 9.25%,a fill factor（FF）of 67.86%,and PM6:PCl based device obtained a PCE of 10.02%,a FF of 70.25%.3.In order to study the effect of 1-chloronide additive and thermal annealing treatment on the performance of the devices.The polymer acceptor P2TF was obtained by polymerization of IDIC-C16 and 3,3’-difluoro-2,2’-bithiophene,and the charge transfer kinetics of PM6:P2TF based devices were studied by time-resolved transient absorption.It was found that additives and thermal annealing can optimize the morphology of the active layer and improve the charge transfer rate between the donor acceptors.In addition,PM6:P2TF also has excellent bending performance,indicating its great application potential in flexible all-polymer solar cells.4.At present,the active layer of organic solar cells is mainly processed with halogen solvent,which is not conducive to commercial production in the future.We designed and synthesized two asymmetric polymer donors PBDT-F-2TC and PBDT-SF-2TC,which can be processed by green non-halogen solvent.The devices were prepared using 1,2,4-trimethylbenzene solvent,PBDT-F-2TC:IT-4F based device achieves a PCE of 10.29%,PBDT-SF-2TC:IT-4F based device achieves a PCE of 10.39%.5.Although fluorinated or chlorinated polymer donors can improve the performance of organic solar cells,how to rational introduction halogen atoms into polymer donors is very important when designing organic photovoltaic materials.We synthesized PBDT-F-3T2C containing fluorine atom and PBDT-Cl-3T2C containing chlorine atom,which can be processed by green non-halogen solvent,the effects of fluorine and chlorine atoms on polymer donor materials were systematically compared.It can be found that both chlorine atom and fluorine atom can effectively reduce the molecular energy levels,although fluorine atom is more electronegative than chlorine atom,the 3d orbital of chlorine atom can hold more electrons implying that chlorine atom can lower the molecular energy level of the material more effectively.and chlorine atom has a stronger ability to withdraw electrons than fluorine atom.The devices were prepared using chlorobenzene solvent,PBDT-F-3T2C:IT-4F based device achieves a PCE of 11.67%,PBDT-Cl-3T2C:IT-4F based device achieves a PCE of 10.19%.In addition,the devices were prepared using1,2,4-trimethylbenzene solvent,PBDT-F-3T2C:IT-4F based device achieves a PCE of10.04%,PBDT-Cl-3T2C:IT-4F based device achieves a PCE of 5.83%.The results show that rational introduction of halogen atoms into donor materials can improve the PCE of organic solar cells.6.To match non-fullerene acceptors with low LUMO（lowest unoccupied molecular orbital）levels,polymer donors with deep HOMO（highest occupied molecular orbital）levels and high planarity need to be developed to further improve the PCE of devices.Due to the strong electron-withdrawing effect of4,4’-dinonyl-2,2’-bithiazole（BTz）unit,the HOMO level of PBDTBTz can be significantly reduced to-5.60 e V.Meanwhile,the noncovalent conformational lock（N···S）of BTz can improve the planarity of the material,which is beneficial to charge transfer and molecular stacking.The device based on the PBDTBTz:IT-4F achieves an VOC of 0.92 V.Furthermore,the device work well with a negligible driving force(ΔEHOMO)of as small as 0.06 e V.These results revealed that combination of electron-withdrawing bithiazole and double noncovalent conformational lock of N···S is a promising molecular design concept of polymer donor with deep HOMO level and planar structure for high performance organic solar cells. |
