Constitution Of Non-fullerene Acceptors Based On Different Push-pull Effects And Investigation Of Optoelectronic Properties

With the depletion of traditional fossil energy and the deterioration of the ecological environment,vigorously developing green,efficient and safe clean energy has become a global consensus.The development of new high-efficiency and low-cost photovoltaic power generation technology is becoming one of the key means to promote my country’s energy transformation and achieve the national green and sustainable development strategic goals.Among them,organic solar cells（OSCs）have attracted much attention because they can be fabricated into lightweight,ultra-thin and large-area flexible devices.At present,the development of non-fullerene acceptor materials are the key to realizing higher-efficiency organic photovoltaics and ultimately industrialized applications.How to balance and control the absorption spectrum expansion,energy level matching,nano-scale phase separation morphology and carrier transport improvement of non-fullerene fused-ring acceptor materials,and further breaking through the current efficiency bottleneck has become a difficulty in current scientific research.Therefore,exploring the innovative design of high-efficiency non-fullerene acceptor structures have positive significance for breaking through the bottleneck of research efficiency of organic photovoltaic materials and devices,and promoting the application and development of high-efficiency organic photovoltaics.In this research paper,we focus on the strategic structural design of non-fullerene electron acceptor molecules,and guide the non-fullerene electron acceptors through in-depth study of the structure-activity relationship between the acceptor moleculars structure and photovoltaic parameters in the device,and direct the structural optimization design of non-fullerene electron acceptors to achieve high-efficiency organic photovoltaic cells.The first chapter mainly describes the working principle,device structure,acceptor materials,development history of organic solar cells,and summarizes the current research status at domestic and abroad.In the second chapter,A-DA’DA-type based benzodithiazole central core was precisely synthesized by substituting the side chain of alkane octyl phenyl at the nitrogen position of the pyrrole ring on the Y6 molecular skeleton and introducing a strong electron-deficient group at the end,named BTS-IC2F and BTS-IC2Cl.The strong push-pull effect between the intramolecular D-A or A’units and the squeezing effect of the in-plane bending growth of the large arylalkane octyl group in the side chain extend the absorption of the chlorine-substituted end-group BTS-IC2Cl fused-ring acceptor to 1000 nm in the infrared region and the optical band gap reaches 1.23e V,which ranks among the highest spectral absorption values of current non-fullerene fused-ring acceptors.Compared with the fluorinated acceptor BTS-IC2F,the chlorinated acceptor BTS-IC2Cl obtains a lower LUMO level.The polymer donor PM6with matching spectral absorption and the non-fullerene fused-ring small molecule acceptor are selected to prepare a single-section two-component,which are optimized by blending the donor/acceptor ratio,additives and thermal annealing.PM6:BTS-IC2F and PM6:BTS-IC2Cl blend films obtain the highest photoelectric efficiencies of 12.11%and 12.96%,respectively.The high photoelectric efficiency of the chlorinated BTS-IC2Cl is attributed to the enhancement of J_sc,which is mainly due to the wider solar photon capture range and better balanced hole/electron transport capacity of the PM6:BTS-IC2Cl blend film.In the third chapter,by adopting the strategy of fused-ring small molecule acceptor polymerization and configuration regulation of polymer end-group sites,a precise synthesis of alternating flexible heterocyclic donor units based on selenium heterocyclic central core fused-ring rigid acceptor units are precisely synthesized by Stille coupling polymerization the D-A-type regioregular non-fullerene polymer acceptors,named PBTSe-C20S and PBTSe-C20Se.Compared with the thiophene unit,the PBTSe-C20Se constructed with the electron-rich selenophene unit has an obvious red shift in the spectral absorption due to the stronger push-pull effect formed in the molecule;Cyclic voltammetry electrochemical tests show that the energy level of the polymer acceptors are suitable,which could match the energy level of the polymer donor PM6.By optimizing the device process such as donor/acceptor dosage,additive content and thermal annealing treatment of the active layer,PBTSe-C20S is blended with wide-bandgap polymer PM6 to obtain an organic solar cell with a preliminary photoelectric efficiency of 6.25%.The device performance is being further optimized.In the fourth chapter,using the strategy of fused-ring small molecule acceptor polymerization and polymer end group configuration regulation,based on selenium heterocyclic central core and fused-ring rigid acceptor unit alternating acceptor units are precisely synthesized by Stille coupling polymerization,A-A’-type non-fullerene polymer acceptor BTSe-1F2 and regioregular non-fullerene polymer acceptor BTSe-2F2 are synthesised.Both polymer acceptors show good solubility in common solvents chlorobenzene,chloroform and dimethyl sulfoxide,indicating that they have good processability and compatibility.Compared with the isomerized acceptor BTSe-1F2,the regioregular acceptor BTSe-2F2 exhibits a stronger red-shifted absorption,which is attributed to the conformational regulation that contributes to the improved polymer chain regularity and the formation of more strongπ-πstacking morphology.The absorption spectrum of BTSe-2F2 extends to 955 nm in the near-infrared region,and its optical band gap is 1.30 e V.Cyclic voltammetry tests characterize the LUMO levels of BTSe-1F2 and BTSe-2F2 as-4.01 e V and-3.82 e V,respectively,and higher LUMO levels can realize high open-circuit voltage.The device performance is currently being tested.