Synthesis And Application Of New Non-fullerene Acceptor Materials Based On 3D Skeleton

Among various photovoltaics technologies,organic photovoltaics(OPVs),whose building blocks are based on earth abundant organic materials,have the advantages of light weight,flexible fabrication,and being compatible with plastic substrates,which make them the promising candidates for the next generation PV technologies.OPV is an area of great interest driven by the rapid improvement of device efficiencies of non-fullerene based systems in recent years.To date,a single-junction OPV has achieved a power conversion efficiency of 18%.OPVs are at the dawn of commercialization.This is mainly due to the proposal and wide application of linear fused ring"acceptor-donor-acceptor"(A-D-A)design strategies.Its molecular design is mainly concentrated in three parts:fused ring core,solubilizing side chains,and electron-withdrawing end groups.Among them,the fused ring core is crucial to regulate the photoelectric properties and intermolecular interactions,which in turn affects the photovoltaic performance.Introducing the spiro-like 3D structure into the fused ring core can optimize the intermolecular stacking,avoid excessive aggregation and ensure an effecient intramolecular charge transport channel.The anchor point of this thesis is the synthesis of novel non-fullerene acceptor materials based on the 3D skeletons.Our work mainly has the following aspects:(1)First,we incorporated spirobifluorene units in the 1D A-D-A fused ring system.The spirobifluorene unit linked together by a sp3 spirocarbon atom has a orthogonal orientation,which can inhibit excessive aggregation.The rigid skeleton reduces the non-radiative energy loss simultaneously,which is beneficial to improve the device performance.So we designed and synthesized two materials,SFT6-4F with heptacyclic core and SFT8-4F with nonacyclic core.With a high open circuit voltage of 0.97 V and good absorption in the visible region,SFT8-4F has achieved an average efficiency of 12.1%when combined with polymer donor PM6,and it has achieved a PCE of 15.9%with a near-infrared-absorbing rear battery.(2)To explore the effect of 3D molecular structure on device performance,we introduce a 3D configuration into the acceptor material.The bicarbazole connected by nitrogen-nitrogen bond has an orthogonal structure similar to spirobifluorene,and the carbazole unit has a stronger electron donating ability than the fluorene unit,which is favorable to form effective interchain ?-? overlap and enhance intermolecular charge transport.Based on the electron-rich carbazole and bicarbazole units,we designed and synthesized 926CZ-4F with a 1D nonacyclic core and 99CZ-8F with a 3D spatial structure,respectively.99CZ-8F can be considered as a 3D non-fullerene acceptor formed orthogonally by two 1D A-D-A non-fullerene acceptors.After optimizing the PM6:99CZ-8F active layer with a binary solvent system,its PCE reached 6.6%,which is among the best reported values for 3D non-fullerene electron acceptor based OSCs.(3)In chapter 4,we adopt the A-D-A-D-A strategy by introducing a distorted electron-withdrawing group into the acceptor material to enhance the intramolecular charge transfer,reduce the band gap,and broaden the absorption spectrum.The BTP(8,8'-biindeno[2,1-b]thiophenylidene)unit formed by carbon-carbon double bonds has a unique ? electron system.BTP can satisfy the 14-? electron rule after receiving an additional electron,and at the same time the molecule is twisted by a certain degree to relieve the intramolecular steric strain.So the BTP derivatives are expected to show near-infrared absorption above 1000 nm.Since BTP shows cis-trans inter-conversion in solution,we,at present,focus on the enhancement of the stability of BTP.In conclusion,we have included three types of 3D skeletons into non-fullerene acceptors to optimize the charge transfer between donor and acceptor,which could provide new avenues to design efficient non-fullerene acceptors.The results suggest that the non-fullerene acceptors based on the 3D skeletons could suppress the formation of large domains of acceptors by the reducing the strong intermolecular interaction.Meanwhile the morphology of the active layer could be improved with the introduce of 3D acceptors,resulting in good device performance.