Design And Synthesis Of Oligomeric Small Molecule Acceptor Materials And Their Photovoltaic Propertie

Due to the problems existing in fossil fuels(resulting in global warming,air pollution and acid rain),developing renewable resources to replace fossil fuels and eliminating the negative impacts of traditional energy conversion systems on climate and human health is one of the challenges facing mankind today.Polymer organic solar cell(OSC)is considered as the most promising organic solar cell technology with its advantages of light weight,good flexibility and low cost.In 2017,Li Yongfang’s research group proposed the polymerization strategy of small molecule receptor(SMA).The polymerized small molecule receptor(PSMA)has been widely studied.PSMA combines the advantages of small molecule receptor such as narrow band gap,strong absorption,adjustable electron energy level,good film forming performance,more uniform morphology and light stability.In addition,many SMA modules and different conjugate joint units can be selected to adjust the physicochemical properties and photovoltaic characteristics of PSMA.Therefore,PSMA shows excellent energy conversion efficiency.However,the energy conversion efficiency of OSCs based on PSMA is lower than that of OSCs based on SMA.This is because the electron mobility in PSMA films is usually lower than that in SMA films,but the oligomeric small molecule receptors have the advantages of both SMA and PSMA systems.Oligomeric small molecule receptors can exhibit higher electron mobility than PSMAs because they have a well-defined molecular structure that enables intermolecular assembly,low batch to batch variance,and stronger crystal structure.In addition,because the molecular size of the oligomeric small molecule receptor is larger than its component SMA,the oligomeric small molecule receptor has stronger thermal and morphological stability.However,the energy conversion efficiency of OSCs based on oligomolecular receptors is still lower than that of the most advanced OSCs based on SMA and PSMA,so further development of new oligomolecular receptors is needed.The double bond structure of trans vinyl can form a lower torsion Angle between adjacent modules,which can reduce the flatness of the molecular skeleton.The flatness of a molecule affects its intermolecular packing and crystallinity,thus determining its electron transport capacity.Based on this,this paper designed and synthesized A-DA ’D-A type dimerized non-fullerene acceptor material with trans-vinyl bridge,and studied its photovoltaic performance.1.The trans-vinyl bridged dimer non-fullerene acceptor material DSV was designed and synthesized,and a device based on PM6:DSV blended film was prepared,and the optical,electrical,charge transport characteristics and morphology of the blended film were studied.DSV has strong absorption in the visible-near-infrared range of 550-900 nm,which is conducive to making full use of the solar spectrum.The HOMO/LUMO level difference between PM6 and DSV is 0.06 eV and 0.16 eV,respectively,which is beneficial to reduce non-radiative energy losses and thus obtain a large open-circuit voltage(VOC).Through device optimization,it is found that the blended film with 1-CN and thermal annealing has better phase separation morphology,which is conducive to exciton dissociation and charge transport,and improves the short-circuit current density(JSC)and fill factor(FF)of the device.Among them,the photoelectric conversion efficiency of the unoptimized(as-cast)device is 12.7%,which is much lower than the photoelectric conversion efficiency of the optimized device of 15.24%,and its VOC is 0.950 V,JSC is22.25 m A/cm2,and FF is 72%.2、The dimeric non-fullerene acceptor DSV-Cl was synthesized by the introduction of IC-2Cl,and the effects of chlorine substitution on the optical,electrical,charge transport characteristics and morphology of the blended membrane were studied.Miscibility is improved by the introduction of chlorine atoms,which facilitates mixing with PM6 donors.The HOMO/LUMO energy level difference between PM6 and DSV-Cl is 0.17 eV and 0.18 eV,and the large energy level difference ensures the effective dissociation of the charge.The AFM diagram can be observed to form a nanofiber network based on PM6:DSV-Cl films,which is conducive to charge separation and transport.Compared with DSV devices,molecular crystallization is stronger and hole transport capacity is better.It exhibits efficient exciton dissociation and hole transfer,therefore,higher JSC and FF are obtained,showing excellent energy conversion efficiency of 16.8%.