Design And Synthesis Of Novel Polymer Acceptors And Their Application In All-Polymer Solar Cells

All-polymer solar cells（all-PSCs）are favored by researchers because of their excellent device stability and mechanical flexibility.The device efficiency has been improved steadily,and now it has exceeded 17%.However,compared with polymer donors,the development of polymer acceptors with excellent photoelectric properties lags behind,so it is of great significance to develop new polymer acceptors.This thesis aims at establishing a deeper understanding on the structure-property relationship of polymer acceptors via delicate polymer structural control,and provides more theoretical basis for the development of new high-performance polymer acceptors in the future.The specific research contents are as follows.In Chapter 2,a set of random polymer acceptors PNDI-DTBTx were synthesized by introducing the third component into the conjugated backbone of the classic n-type polymer N2200.With the increase of the content of the third component,the regularity of the polymer main chain decreases,which inhibits the excessive aggregation of the polymers.Although the crystallinity decreases,PNDI-DTBT25 can still obtain high electron mobility.At the same time,the all-PSC prepared with PBDB-T as the donor obtained the highest PCE of 7.91%.This is mainly due to its relatively weak aggregation in solution and good miscibility with donors.Meanwhile,the active layer film can maintain a certain degree of crystallinity,so that the phase separation size of the blend film is appropriate.These results show that introducing an appropriate third component to design random copolymer is effective in adjusting the aggregation ability of the polymer acceptors in solution and the crystallization degree in film,which is very important to optimize the morphology and device performance of all-PSCs.In Chapter 3,two novel polymer acceptors PNDI-2Tz-Ph and PNDI-5Tz-Ph with"main chain isomerism"were designed and synthesized.Compared with PNDI-2Tz-Ph,PNDI-5Tz-Ph has a greater degree of main chain torsion,which inhibits the strong aggregation of the polymer to a certain extent.Nevertheless,the electron mobility of PNDI-5Tz-Ph is higher than that of PNDI-2Tz-Ph,which is mainly due to the different influence of"isomerization effect"on their molecular orientation and polymer crystallinity.With PCE10-2F as electron donor,the difference in device performance of all-PSCs is more obvious.Although the power conversion efficiency（PCE）of PNDI-5Tz-Ph is only 2.61%,it is 65 times higher than PNDI-2Tz-Ph,which is due to the formation of fiber-like network structures,tighterπ-πstacking,and longer coherence length.This work is the first time to explore the influence of"isomerization effect"on the performance of all-PSCs from NDI-based polymer acceptors.The isomerization effect also provides an effective strategy for the development of new high-performance polymer acceptors based on NDI in future.Although the polymer acceptors based on NDI unit possesses low production cost,the low light absorption coefficients limited the short-circuit current density(J_sc)and PCE of all-PSCs.On the contrary,polymerized small molecular acceptors have exhibited promising prospect in achieving high-efficiency all-PSCs.In Chapter 4,a novel polymer acceptor PAY-IT was synthesized by selecting the small molecular acceptor with asymmetric skeleton and isomeric pure terminal group as the structural unit.Compared with the"V"configuration of symmetric monomer,the asymmetric monomer shows the"S"configuration.Therefore,the planarity of the resulting polymer PAY-IT will be better,which is conducive to charge transport.With PM6as the donor,PAY-IT offered the highest PCE of 14.91%associated with an open circuit voltage(V_oc)of 0.94 V,a J_sc of 21.73 m A cm^-2,and a fill factor（FF）of 0.73.In addition,three batches of PAY-IT with different molecular weights all offered exceeding 14.40%efficiency,showing the superior batch-to-batch reproducibility.Moreover,the all-PSCs prepared from non-halogenated solvents of o-xylene and tetrahydrofuran（THF）afforded a PCE of 10.66%and11.65%,respectively.This work explored polymerized fused ring acceptors with asymmetric structures for application in all-PSCs for the first time.Overall,this work demonstrated a new design concept for the development of high-performance polymer acceptors with superior batch-to-batch reproducibility and green solvent processability.Although polymerized fused ring acceptors exhibited high device performance,their synthesis is complicated,which is not conducive to commercial application.On the contrary,non-fused acceptors is more facile in synthesis,but non-fused polymerized small molecular acceptors have not been reported.In Chapter 5,two novel polymer acceptors PBTz-TT and PFBTz-TT with A-D-A’-D-A type non-fused ring structures were synthesized.Compared with PBTz-TT,PFBTz-TT exhibits more coplanar structure,higher absorption coefficient,stronger interchain interaction and higher electron mobility due to the noncovalent interaction induced by F atom.All-PSCs were prepared by layer-by-layer deposition method with PBDB-T as donor.The best device efficiency was obtained through the synergistic effect of solvent additive and thermal annealing.A decent PCE of 10.14%was achieved by PFBTz-TT as a result of high J_sc(18.95 m A cm^-2)and FF（0.63）,which is mainly due to the closer and more ordered stacking of the polymer in active layer.This work demonstrated non-fused polymerized small molecular acceptors（non-fused PSMAs）for all-PSCs for the first time.The research results also showed that non-fused PSMAs have broad prospects in all-PSCs.