Spin-Optoelectronic Research In Nonfullerene Organic Photovoltaic System

In recent years,new non-fullerene acceptors(NFA)have been constantly emerging.The performance of organic solar cells based on NFA has been continuously improved,and the single-junction photovoltaic efficiency has exceed 18%.In addition,this kind of materials can be parpered by the solution in low temperature.And the molecular structure has strong plasticity and light absorption characteristics.So,it provides an importance basis for realizing flexible,semi-transparent photovoltaic device.Campared with traditional fullerene acceptors,non-fullerene acceptors have obvious differences in molecular structure and photoelectric response.Therefore,it is important to further study photoelectric properties,especially the dissociation and recombination in excited states and transport of charge carries.This thesis is based on several non-fullerene acceptor materials to prepare the corresponding bulk heterojunction solar cells.We used the experiment tools including magneto-photocurrent(MPC),magneto-photoluminescence(MPL)and impedance spectroscopy test to investigate the photo-physical phenomena related to spin states,trap states,photo-induce polarization and exciton dissociation under photo-excited states.Such basic research can provide important scientific evidence for optoelectronic materials and device physics.The specific work is as follows:(1)Study on spin states,trap states,and photo induced polarization in non-fullerene photovoltaic system:In experiments,it was found that devices based on thiophene-modified ITTC as the acceptor can generate a smaller open circuit voltage and a larger short-circuit current.By studying the morphology,trap state density,magneto-photocurrent of PBDB-T: ITTC and PBDB-T: ITIC blends and corresponding devices,we have discovered triplet-charge reaction play an important role in the photovoltaic process.The reaction can effectively utilize the charge in the trap state to reaction and generate photocurrent,which provides an important clue for the photocurrent increase.In addition,the double beam photo-excitation confirms the existence of dipole-dipole interaction in materials,which can further promote electron-hole dissociation.This task was published in Caixia Zhang,et al.Nano Energy,2020,78,105324 and Caixia Zhang,et al.Journal of luminescence,2020,41(12):1000-7032.(2)Study of spin-drive exciton dissication in non-fullerene photovoltaic system:many non-fullerene bulk beterojunction break the traditional concept of fullerene bulk beterojunction that the dissociation energy generating the energy different donor and acceptor is independent the size of the photocurrent.To clarify this scientific question,we prepared a high efficiency organic solar cell based on PTO2:IT-4F and investigate the electron-hole dissociation process associated with spin states.By using magneto-photocurrent,we found that the charge transfer state of polymer-nonfullernen solar cell can effectively the singlet dipole pair.Compared with the triplet state,the singlet state has stronger dissocation rate and smaller exciton binding energy.Therefore,we conclude that the non-fullerene system can obtain high-density singlet excitons,and this effect provides the necessary conditions for the photocurrent gain.This paper has 32 figures,6 tables,and 194 references...