Synthesis And Photovoltaic Properties Of Small Molecule Acceptor Materials Based On Naphthimide

With the development of organic solar cells（OSCs）,the shortcomings of using fullerenes as acceptor materials have gradually become prominent.Non-fullerene small molecular acceptors have many advantages such as feasibly chemical modification,adjustable absorption and energy levels,strong absorption in the near-infrared range,excellent solubility and good morphological stability.This thesis provides a systematic overview of the research progress in OSCs in order to understand the source of ideas for designing novel non-fullerene acceptor materials.In response to the key problems such as few types of naphthalimide-based small molecular acceptors,and the relationship between molecular structure and performance are still unclear,a series of small molecular acceptors with star-shaped and linear structures based on naphthalene diimide（NDI）units are developed.The effects of different structures on the photovoltaic performance are compared systematically for revealing the relationship between the molecular structures and photovoltaic performance.The most substance and conclusions of the thesis are as follows:1.Two star-shaped small molecular acceptors（TPA-NDI and Tr-NDI）based on naphthalene diimide as acceptor unit,and triphenylamine and trimeric indene as donor units are designed and synthesized,respectively.The effects of different donor cores on the photophysical properties,electrochemical properties and photovoltaic performance of star-shaped acceptors are systematically studied.The different donor cores present significant effects on the molecular planarity and photovoltaic characteristics.The small molecular acceptor with triphenylamine as the donor core shows better intramolecular aggregation and photovoltaic characteristics,and has higher photovoltaic performance than the Tr-NDI with an excessively twisted molecular skeleton.The power conversion efficiency（PCE）of the PBDB-T:TPA-NDI based device is 2.71%,which is 1.9 times higher than that of the PBDB-T:Tr-NDI based devices with the open circuit voltage(V_oc),short circuit current(J_sc)and fill factor（FF）of 0.935 V,5.23 mA/cm² and 55.45%,respectively.2.Two small molecular acceptors（SF-NDI and F-NDI）are designed and synthesized with spirofluorene and fluorene as the donor units,and naphthalene diimide as the acceptor unit,respectively.The significant influences of different donor cores on the photovoltaic properties of these small molecular acceptors are systematically studied.Through thermal,photophysical and morphological tests,the star-shaped small molecular SF-NDI with spirofluorene as the donor core has better intramolecular aggregation,higher photovoltaic characteristics,better thermal stability,compared to the linear small molecular F-NDI based devices.The highest PCE based on PBDB-T:SF-NDI is 3.59%,with the corresponding J_sc of 6.25 mA/cm² and the FF of 59.9%,respectively,which is slightly higher than the efficiency of the PBDB-T:F-NDI based devices.3.Two small molecular acceptors（B-NDI and BP-NDI）are designed and synthesized based on naphthalene diimide as acceptor unit,and the smaller biphenyl and benzene as the donor center cores,respectively.Compared to the B-NDI with benzene as the donor core,the star-shaped BP-NDI with biphenyl as the donor core shows the better intramolecular aggregation,photovoltaic characteristics and better thermal stability.The PCE based on PBDB-T:BP-NDI is 3.23%with the V_oc,J_sc and FF of 0.896 V,6.75 mA/cm² and 53.39%,respectively,which are higher than the PBDB-T:B-NDI based devices.