Novel Perylene Diimide Based Electron Acceptors: Design,Synthesis And Performance Research

Perylene diimide(PDI)derivatives were widely used as acceptors in organic solar cells(OSCs)due to the strong absorption,ease of functionalization and excellent stability.PDI molecules usually display strong π-π intermolecular interactions owing to the planar configuration,which can result in a high electron mobility.However,the excessive self-aggregation will lead to large scale phase separation in OSCs,which is highly detrimental to exciton dissociation and sequentially attenuates the device performance.Therefore,achieving a trade-off between the distortional degree and the conjugated extent to achieve high carrier mobility and efficient exciton dissociation was an effective approach to obtained high performance PDI-based acceptors.In this thesis,a series of acceptors with different conjugation sizes and twisting angles are designed and synthesized based on the first(PDI)and second(PDI2)generation buliding blocks.Additionally,by replacing the ethylene bridge(C=C)with boron-nitrogen(B-N)moiety in PDI2,the third generation buliding block PDI2 BN was obtained.Followings are the main contents and conclusions:(1)Firstly,the three-dimensional TPDI2 molecule and it’s ring-fused derivative FTPDI2 were designed and synthsized using PDI2 as building block.Owing to their well-aligned energy levels as well as the complementary absorption spectra,PTB7-Th was employed as electron donor for constructing the OSC devices.Much higer PCEs were obtained for TPDI2 and FTPDI2 based devices(7.84 % and 8.28 %,respectively)than that of PDI2 based ones(5.57 %),resulting from their larger twist angles.Compared to TPDI2,FTPDI2 poessessed a less twisted configuration but larger π-conjugation,which leaded to an appropriate aggregation behavior,sequentially gave better photovoltaic performance.(2)Secondly,this design principle was applied to a larger molecular system.A three-dimension molecule TPDI3 as well as the ring-fused analogue FTPDI3 were designed and synthesized based on PDI3.TPDI3 exhibited a much higher PCE(8.84 %)than that of TPDI2(7.84 %)and FTPDI3.This can be attributed to the better banlance between π-conjugation and distortion of TPDI3.As for FTPDI3,the relative less twist angle and larger conjugation resulted in stronger aggregation and inferior PCE referred to TPDI3.Thus,a trade-off between twisting angle with conjugation size is a key issue for high performance PDI based acceptors.(3)Additionally,a series of dendritic PDI derivatives with were designed and synthesized by adjusting their conjugation expansion pathway.It was shown that TTPDI,which contained large twist angle and small conjugation size exhibited the lowest PCE of 6.48 %.However,significant increasion in PCE can be achieved by either decreasing the twist angle(TFTPDI,7.77 %)or increasing the conjugation size(TTPDI2,7.25 %).Thus,the conclusion mentioned above was further verifiled.(4)Finally,PDI2 BN and PDI3 BN molecules were designed and synthesized by replacing the C=C bridge with B-N unit in PDI2 and PDI3.Their optoelectronic properties and molecular geometry were characterized by UV-vis spectra,CV as well as DFT calculation.Both PDI2 BN and PDI3 BN exhibited a strong absorption and excellent thermal stability,together with their advantages of cost effective synthesis making them an ideal next-generation building blocks.In summary,a series of three-dimensional PDI-based molecules as well as new generation PDI building blocks were designed and synthesized.The structure-performance relationship was deeply investigated and discussed.This thesis will provide a guidance for the further development and application of PDI materials.