Theoretical Study On The Relationship Between Structure And Performance Of Heterojunction Cells Containing Non-fullerene Acceptors

Social progress cannot be separated from the use of energy.Given the increasingly severe environmental pollution and the depletion of fossil energy exploitation,it is urgent to develop new clean energy and implement the goal of carbon neutrality.Organic solar cells（OSCs）have the advantages of flexibility,convenient molecular modification,and low price,which stand out among various solar cells.In recent years,many researchers have carried out regulation based on strategies such as molecular design and device optimization,while refining and improving the internal working mechanism of OSCs from a microscopic perspective is complementary to macroscopic experiments,deeply understanding the photoelectric conversion mechanism,and identifying the essential relationship between material structure and performance,which is conducive to ultimately achieving precise guidance of microscopic mechanisms for material design and device preparation.In this thesis,the dithienothiophen[3,2-b]-pyrrole-benzothiadiazole（BDP）,chlorinated BDP-2Cl,BDP-4Cl,and designed BDPN-4Cl have been investigated.One performed the density functional theory（DFT）and time-dependent density functional theory（TD-DFT）to study their electronic structures,frontier molecular orbitals（FMOs）,and other photoelectric parameters,which showed that designed BDPN-4Cl displayed narrower band gaps,smaller reorganization energy,and electrophilic parameters than prototypical non-fullerene acceptors（NFAs）.It had a more excellent charge separation rate/charge recombination rate ratio for heterojunction system PM6/BDPN-4Cl,which was conducive to the interfacial process.Furthermore,one also estimated the ideal performance(V_OC,V_loss,J_SC)of all the compounds estimated by the macroscopic scale model to reveal the influence of halogen atomic substitution andπ-extension at the end-capping on performance.Secondly,several non-fused ring asymmetric NFAs were studied and designed to explore the photoelectric conversion mechanism under this structural system.The skeletons were constructed by a central 1,4-dimethoxybenzene core and flanked by different dithieno-pyrroles and thiophene derivates as electron-donating groups;the end-capped groups were composed of two 1,1-dicyanomethyl-3-indanone.Theoretical calculations show that the designed DBPT-series have broader absorption spectra,larger electron-accepting power,and greater separation distance between holes and electrons.The DBPT-series also yielded enhancement mobility,which may relate to the significant dipole moment and electronic coupling.In addition,one constructed the device models using PBDB-T as the donor.The results show that the optimized blends of PBDB-T/DBPT-4F achieved more intermolecular fragment charge amounts,charge transfer states,and smaller binding energy.Then,under the Scharber model,the device PBDB-T/DBPT-4F performs better properties.Overall,based on the different electronic structures of NFAs,systematic research on the essential relationship between molecular structure modification and performance can provide theoretical support for further design,synthesis and development of efficient NFAs.