Performance Study Of Biomass Interface Materials Based On Nucleobase In Organic Solar Cells

In recent years,with the large consumption of global natural resources,the awareness of environmental protection is gradually awakening,dying to develop new environment-friendly resources to replace traditional energy.Solar energy is a sustainable energy with rich global resources,convenient access and low carbon emission.It is one of the green energy that can effectively solve the global energycrisis.Photovoltaic technology,which directly converts solar energy into electric energy,has become a hot research field.Organic solar cells(OSCs),one of the new photovoltaic technology,possess advantages of low cost,solution processing and light weight.They have the potential to construct flexible wearable electronic devices.With the rapid development of non-fullerene active materials,the power conversion efficiency(PCE)of bulk heterojunction OSCs has exceeded 19 %.At present,the efforts to improve the performance of OSCs mainly focus on active layer optimization,device structure design and interface engineering.Through the modification,interfacial materials can regulate the energy level matching of the electrode/active layer interface,prevent the damage of physical phenomena or chemical reactions on the active layer,improvide functional modification such as wettability and conductivity,and finally enhance the mobility of carriers in the device,as well as improving the collection and extraction of charges at electrodes.Therefore,interface engineering is one of the effective ways to improve the performance of OSCs.From the perspective of interface engineering,the nucleobase-derived materials were used as electrode modification materials to investiagte their effects on the photovoltaic performance of devices.The main research contents are as follows:(1)The adenine-derived small molecular: N9,N9’-trimethylene-bisadenine(AA)was firstly dissolved in 2,2,2-trifluoroethanol(TFE)and modified with ZnO nanoparticles to prepare cathode interlayer(CIL)in inverted organic solar cells(i OSCs).The results show that the the energy level of ZnO films can effectively regulate by AA,as the work function(WF)value of ZnO films is reduced from 4.79 e V to 4.46 e V.In addition,the leakage current of devices under dark is decreased,which confirms the AA as modifier inhibits the recombination of carriers.ZnO:AA nanoparticle films were prepared under lower temperature(60 °C)without high temperature(150 °C)annealing.The PCE of fullerene(PTB7:PC71BM)and non-fullerene(PM6:Y6)based i OSC devices fabricated by ZnO:AA films increased from 7.29 % and 14.31 % to 8.77 % and 15.63 %,respectively.(2)Following the exploration of AA,we investigated the performance of i OSCs based on ZnO nanoparticles films modified by adenine-derived polymer poly(9-(4-vinyl benzyl)adenine)(PA).Without thermal annealing,ZnO films with PA modification showed excellent performance in i OSCs based on fullerene and non-fullerene active layers.Especially,the PCE value of i OSCs based on non-fullerene(PM6:Y6)can reach 16.22 %,which is among the highest efficiencies reported for i OSCs.ZnO:PA films,worked as CIL,could reduce interface contact resistance and surface WF,inhibit the internal carrier recombination,and achieve effective carrier extraction and collection.Benefit of the increased electrical conductivity,the PA-modified ZnO films are thickness insensitive,affording high performance i OSCs over a wide interlayer thickness range,from 18 nm to 100 nm.They can be used for large-area processing technology.(3)Two nucleicbase-derived polymers PA and Poly(1-(4-vinylbenzyl)thymine)(PT)with different nucleicbase units were used as the high WF electrode modifiers to study the effects of biomass-derived materials on the performance of organic electronic devices.According to the DFT calculation,the polymer repeat units of PA and PT have strong molecular dipole moments,which can form interface dipoles with the electrode materials and regulate the interface WF.Through ultraviolet electron spectroscopy(UPS)and kelvin scanner(SKP)measurements,it is proved that two nucleicbase-polymers significantly reduced the WFs of silver(Ag),gold(Au)and indium tin oxide(ITO),which was consistent with the DFT calculation results.Polymer PT,possessing a stronger molecular dipole moment in thymine subunit,has stronger ability to adjust the interface WF.With the optimized thickness(~9 nm)corrected by X-ray photoelectron spectroscopy(XPS),PA and PT can be widely used in optoelectronic devices for electrode modification,such as OSCs,perovskite solar cells and organic field effect transistors.The PM6:Y6 baesd OSCs with PA CIL showed a higher PCE value,and maximum PCE reached 17.2 %,which is one of the highest efficiencies reported in biomaterial as CILs.