Design,Synthesis And Photovoltaic Properties Of High-efficiency Non-fused Ring Small Molecule Acceptors

Organic solar cells have become one of the research hospots in the field of organic optoelectronics,because of its unique advantages such as light weight,wide sources,low cost,and solution processability.With the successful application of non-fullerene acceptors to organic solar cells,the efficiency of single-cell organic solar cells based on A-D-A’-D-A type fused-ring small molecule acceptor material Y6 and its derivatives has exceeded 19%.However,the fused-ring small molecule acceptor material contains a multi-fused-ring molecular backbone in the center,which requires covalent ring closure to connect adjacent aromatic hydrocarbons.The synthesis is usually complicated and involves multi-step synthesis and purification,resulting in low overall yield and high material cost,which will limit the large-area device preparation and commercial application of organic solar cells.In order to overcome the shortcomings of the commercialization of fused-ring small molecule acceptors,a molecular design of non-fused ring structures was proposed.This graduate thesis is focuses on A-D-A’-D-A type non-fused ring small molecule acceptors as the research object,a series of new and efficient non-fused ring small molecule receptors are designed and synthesized in this paper.Meanwhile,the relationship between non-fused ring molecular structure and device performance were studied in detail,which provides guidance for the development of new and efficient non-fused ring small molecule acceptors and design strategies for non-fused ring small molecule acceptors.The specific research work and results are as follows:1.Two A-D-A’-D-A type non-fused ring small molecule acceptors 2T2CSi-4F and4T2CSi-4F based on diester-thieno[3,2-b]thiophene unit as the non-fused ring core were designed and synthesized.It has been found that the non-fused ring core based on diester-thieno[3,2-b]thiophene can form multiple non-covalent bond interactions,thereby forming multiple intramolecular conformationally locks in the molecule,which effectively restricting the rotation of single bonds,and making the formation of rigid and coplanar non-fused ring structure,thereby improving molecular accumulation and charge transport.In addition,devices based on PBDB-T:2T2CS i-4F and PBDB-T:4T2CS i-4F obtained a power conversion efficiency of 10.04%and 3.63%,respectively.In addition,the performance of the active layer of the two non-fused ring small molecule acceptors was further studied through morphological analysis and characterization.The PBDB-T:2T2CS i-4F device has higher crystallinity and a face-on stacking structure which favorable for charge transport,thereby forming a fibrous nano-interpenetrating network structure.This study shows that the introduction of non-covalent bonds is an effective strategy to improve the planar ity and device performance of non-fused ring molecules,and the strategy of diester-thiophene units and multiple intramolecular conformationally locks can construct efficient and low-cost organic solar cells.2.Designed and synthesized a new aromatic imide electron-deficient unit dithienophthalamide（DTP）for the construction of non-fused ring small molecule acceptor material DTPEH-4F.It has been found that the non-fused ring small molecule acceptor based on the electron-deficient unit of DTP has suitable energy level and absorption,which can be well matched with PM6,and it reaches a high open circuit voltage of 0.93 V,and the devices based on PM6:DTPEH-4F obtained a power conversion efficiency of 8.27%.In addition,the DTP unit of the fused ring structure serves as the central core,and its rigid fused ring structure improves the overall molecular planarity and close the molecular packing,resulting in a good morphology and high carrier mobility,and the introduction of alkane on the imide group improves the blending morphology and solubility,forming a fibrous nano-interpenetrating network structure.The study shows that DTP unit combines the characteristics of fused ring π-core and imide unit,which provides a reference for the design of novel and strongly electron-deficient acceptor molecules in the central core,and is expected to construct efficient organic solar cells.