Rational Engineering On Non-planar PDI Dimers As Organic Phorovoltaic Acceptors

Recently,significant progress has been made in the emerging field of bulk-heterojunction(BHJ)organic photovoltaic cells(OPVs).Nonetheless,there is still a long way to go before its large-scale commercialization realized the commercialization.The engineering,fabrication and mutual matching of the active layer of OPV devices,composed of the electron-donor(D)and electron-acceptor(A)materials,is crucial to improve power conversion efficiency(PCE)by with the development of quantum chemistry,the design and screening of active materials would leveopen the windows to develop the the oriented synthesis high-performance acceptor materials.Non-fullerene materials have beeen paid more attention due to excellent electron accepting properties,easily tuned energy levels and optical absorption,synthetic versatility etc.Among them,perylene diimides(PDIs)materials as one kind of representative non-fullerene acceptors have captured more attention of the researchers because of their high stability,strong assembly tendency and remarkable optoelectronic properties.However,the performance of traditional PDI acceptors is not very potential on account of the property of overstrong self-aggregation caused by the large ?-conjugated system in the OPVs.Hence,linking two PDI units constructing nonplanar dimers would become an effective strategy to suppress crystallization to design high-performance nonfullerene acceptors.This paper mainly includes three parts of work:1.Theoretical design for nonplanar PDI dimers with planar PDI units.For breaking molecular rigidity and planarity,it is an executable way to increase the distortion between two PDI units.A class of PDI dimers were designed via bridging different linkers in bay positions(1-1' bridge)and headland positions(1-2'bridge)to screen suitable acceptor materials for OPVs.Density functional theory(DFT)and timedependent density functional theory(TD-DFT)calculations were performed to investigate their electronic structures,open circuit voltage(VOC),driving forces(?EL-L),and some major parameters related to the short-circuit current density(Jsc)such as absorption spectrum and carrier transport ability.Meanwhile,engineering different aromatic bridges into the PDI dimers could avoid large torsion angle between the two planar PDI units.By the means of electronic structures,frontier molecular frbitals,open circuit voltages,driving force,absorption spectra and charge transfer rates,investigated 1-2' bridged PDI dimers exhibit more favorable properties as acceptors in OP Vs,which might provide theoretical prediction for the design and synthesis of new OPV SMAs.2.Theoretical design for bowl-shaped PDI dimers with N-annulated PDI units.The molecular backbones also take great effect on the photoelectric properties.To further render PDI derivatives soluble and tailor selfassembly,the incorporation of N-annulations in PDI dimers becomes an effective strategy in latest researches.Here,we focus on engineering PDI dimers with N-annulated bridges to construct bowl-shaped PDI dimers with the aim of improving efficiency,stereoscopic dimensions and the electron transfer abilities by introducing different functional linkers in N-annulated bridges.Besides some properties relevant to photovoltaic performance of these investigated acceptors were characterized by electronic structures,frontier molecular frbitals,open circuit voltages,driving force,absorption spectra and charge transfer rates,etc.Our results demonstrate that,compared to planar N-annulated PDI dimers,bowl-shaped PDI dimers would be more favorable to optical performance.We expect that these modified N-annulated PDI dimers could become potential acceptor materials in OP Vs.3.Theoretical design for star-shaped PDI dimers with functional centre-linkers.On the basis of the previous work,for proving the superiority of N-annulated PDI units,we design theoretically a series of star-shaped PDI dimers with three dimensional geometrical configurations.Meanwhile,considering the functional centre-linkers and different positions could influence the geometrical configuration and photovoltaic performance,we rationally design star-shaped PDI dimers linking bay-position and ortho-position with centre-linkers d,e,f and g.Based on relevant reports,our project will take advantage of star-shaped PDI dimers such as favorable phase separation,block aggregation and isotropic transmission.And we hope our efforts could propel the BHJ OSCs forward.