Design,Synthesis And Performance Study Of Dopant-Free D-A Type Polymeric HTMs

Perovskite solar cell(PVSC)as a promising new generation of thin-film photovoltaic technology has drawn tremendous attention within the past decade.PVSC has experienced a remarkable rise in its power conversion efficiency(PCE)from 3.8% to 25.7%,which was greatly boosted by the outstanding photoelectric performances of perovskite active layer and the merits of the functional layers.As one of the essential functional layers in PVSC,hole-transporting layer(HTLs)is vital in extracting and transporting charge carriers,and can also play a role as interface modification layer between perovskite and anode.Furthermore,HTL offers protection to perovskite from moisture,oxygen,and mis-diffused atoms in the conventional n-i-p PVSCs.At present,the benchmark hole-transporting materials(HTMs)in state-of-the-art PVSCs is 2,2′,7,7′-tetrakis-(N,N-di-pmethoxyphenylamino)-9,9′-spirobifluorene(spiro-OMe TAD).However,the spiroOMe TAD suffers from the low carrier mobility,thus needing to be doped with 4-tertbutylpyridine(t-BP)or lithium bis(trifluoromethanesulfonyl)imide(Li TFSI),which increases the overall cost of device while also compromising its long-term stability.It is therefore a challenge,but also an issue highly necessary for the commercialization of PVSCs,to explore low-cost and high-efficiency polymeric HTMs.Based on the above problems,aiming at developing high-performance and low-cost hole-transporting materials,this dissertation summarizes some intrinsic rules on the structure-efficiency relationship of dopant-free hole-transporting materials.The main contents are listed as follow:1.Three polymeric HTMs PDPP-O,PDPP-T,and PDPP-Cz with different side chains were designed and synthesized by using pyrrolopyrrole-1,4-dione(DPP)as electron acceptor unit and benzodithiophene(BDT)as electron donor unit,in which alkoxy,thiophene,and carbazole serves as side chain of BDT.The PVSCs based on PDPP-O,PDPP-T,and PDPP-Cz exhibited the PCE of 7.92%,10.78%,and 14.96%,respectively.2.Three polymeric HTMs PBTB-1,PBTB-8,and PBTB-12 were designed and synthesized using BDT with carbazole side chain as electron donor unit and benzothiadiazole(BT)as electron acceptor unit with different length alkyl chain.The devices based on PBTB-1,PBTB-8,and PBTB-12 exhibited PCE of 7.92%,10.78%,and14.96%,respectively.The results show that the selection of appropriate length alkyl chain has a crucial effect on the performance of the device.3.Two polymeric HTMs PBTz-8 and PBTz-26 were designed and synthesized by using BDT with carbazole side chain as electron donor unit and benzotriazole(BTz)with different side chain as electron acceptor unit.The effects of side chain branching on the photoelectric properties,energy levels,molecular stacking,and hole mobility were systematically studied.The results show that PBTz-26 with branch chain has better molecular stacking and hole mobility than PBTz-8 with straight chain.The device based on PBTz-26 achieved the highest PCE of 19.83%.4.Two D-A polymeric HTMs PBDBT and PBDBTT were designed and synthesized by using BDT unit with carbazole side chain as electron donor unit,benzodithiophen-4,8-dione(BDD)as electron acceptor unit,and thiophene and thienothiophene as π bridge,respectively.The effects of π bridge conjugation on the photoelectric properties,energy levels,molecular stacking,and hole mobility were investigated.The results show that PBDBT with thiophene as π bridge not only has deeper HOMO level,but also exhibits better molecular stacking and hole mobility.PBDBT-based devices achieved a promising PCE of 22.06%,while PBDBTT-based devices only achieved a PCE of 18.29%.