Research On Charge Energy Transfer Behavior Between Donor And Acceptor In Opv

Non-fullerene organic solar cells(NF-OSCs)become a hot point with higher and higher power conversion efficiencies(PCEs)as the advantage of facile synthesis,adjustable energy levels and designable structures.In non-fullerene OSCs,the energy offset of HOMO level between donor and acceptor is quite different in fullerene system as the unchanged energy level of PCBM.As a result,the physic mechanism of PHT process changed need to be noticed which has not been researched wildly.The research and understanding of the physical mechanism of charge transfer behavior will help us to achieve more efficient OSCs,and have guiding significance for material synthesis and device preparation.For fullerene OSCs,due to the fixed energy level of fullerene and its derivative materials,the light absorption is weak.So,the research on the corresponding PHT process is very rare.For this reason,we selected the PTB7-Th:PC₇₁BM system to study the charge transfer behavior of the devices under different conditions,including using different proportion of additives,changing the annealing temperature and the D/A ratio,and using different solvents.We found that when 3%DIO is used as an additive,the morphology of the active layer is the best,and the charge transfer efficiency of the corresponding device is the highest.However,the higher the annealing temperature,the more obvious the PET process efficiency of the donor material PTB7-Th decreases.Correspondingly,the morphological phase size of the active layer becomes larger and the roughness increases.Next,we found the photoelectric conversion efficiency of the corresponding absorption range is enhanced in the device with a high acceptor content,due to the increase in the absorption of the acceptor,and the photocurrent is significantly improved.Therefore,a more balanced charge transfer process will be obtained.At last,when CF is used as a solvent,the active layer has a larger phase separation size,which is particularly unfavorable for the PET process of the donor material PTB7-Th,and the device performance is low.For the non-fullerene material system,PM6:Y6 is selected for the study of charge transfer behavior.First,the active layer was treated with 1%DIO,1%CN and no additives.The morphology size of the active layer prepared by using DIO as an additive is too small and the roughness is large,while the active layer with CN as an additive has better phase structure and stronger absorption.Compared with no additive system,the weaker range of absorption is supplemented,so that the device obtains a more balanced and efficient charge transfer process.Then,comparing non-annealing and 110°C annealing treatment,it can be found that the annealing treatment enhances the crystallinity of the films.This morphology is conducive to the charge transfer of the acceptor material Y6.Unlike fullerene materials,annealing will optimize the morphology of the active layer of non-fullerene devices and obtain a more balanced and efficient PET and PHT process.Finally,we adjusted the ratio of donor/acceptor of the active layer.Unlike the fullerene system,we found that the non-fullerene active layer system with the D:A=2:1 showed more obvious crystallization.The poor quality of the interpenetrating network leads to unsatisfactory charge transfer process.However,the device with D/A ratio D:A=1:3 is far inferior to the device with active layer ratio D:A=1:1.5,which is mainly due to the low overall charge transfer efficiency in the device with active layer ratio D:A=1:3.The ratio of donor to acceptor has a significant effect on the charge transfer behavior of non-fullerene materials.In the chapter 4 of this paper,the charge transfer behavior of the ternary system is researched.Ternary stargate usually introduces the third component to achieve the complementarity of the spectrum so that the J_SC and V_OCcan be improved at the same time,but the research of charge transfer process is still relatively lacking.The research in this paper shows that when the IT-M content is 80 wt.%,the ternary OSCs of PBDB-T:PC₇₁BM:IT-M achieve the best performance.The study found that by changing the content of the third component,an efficient and balanced PET and PHT process can be obtained.Further studies have proved that the ternary system is an alloy model,so we speculate that this"alloy acceptor"has a deeper energy level than IT-M,thereby increasing the driving force of the PHT process.We further proved that the PET and PHT processes have been effectively improved through PL quenching and IQE experiment;through AFM and TEM test,we found that the introduction of the third component has reduced morphology roughness of active layer and mixed the receptor phase more obviously.The GIWAXS experiment have proved optimize crystal structure.This is conducive to the charge transfer behavior of the device,and this efficient charge transfer behavior also enables the device to obtain the best efficiency.