Photovoltaic Performance Characterization Of A Narrow-bandgap Donor Polymer And Effect Of Binary Solvent Additives Treatment On The Performance Of Polymer Solar Cells

As a new photovoltaic technology,Polymer solar cells(PSCs)have good prospects for appllication due to their advantages of light weight,low cost and the capability to be fabricated into flexible large-area devices.However,comparing to the inorganic counterpart,the photovoltaic performance of PSCs is still lower.Thus,it's a challenge for us to develop efficient devices for PSCs.In order to improve the photovoltaic performance of PSCs,we carried out the research work from following two aspects: the design of donor materials and technology optimization of devices.The specific research content is as follows:1.A new narrow-bandgap copolymer PBFTT,based on 4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene(BDT-F)as donor unit and octyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate(TT)as acceptor unit,was synthesized as donor material for non-fullerene(NF)polymer solar cells(PSCs)application.The optical,electrochemical and photovoltaic properties,the molecular packing and the morphology of the blend films were investigated.The PSCs based on PBFTT: ITIC showed a high PCE of 9.1% with a Voc of 0.94 V,a short-circuit current density(Jsc)of 16.0 m A cm-2,and a fill factor(FF)of 60.5%.Notably,this PCE is among the highest values for the NF-PSCs based on narrow bandgap polymer donor without extra treatments.These results indicate that PBFTT is a promising narrow bandgap polymer donor material for NF-PSCs application.2.A wide bandgap copolymer PBD1 based on meta-alkoxy-phenyl-substituted benzodithiophene(BDT-m-OP)and benzodithiophene-4,8-dione(BDD)have been synthesized in our previous work.Polymer solar cells are fabricated based on the blend of PBD1: IT-4F by using toluene as non-halogenated solvent.When the DIO was used as additive,a high PCE of 10.7% was achieved with a Voc of 0.84 V,Jsc of 19.9 m A cm-2,and FF of 63.8%.When the NMP was used as additive,a PCE of 10.3% was achieved with a Voc of 0.79 V,Jsc of 19.8 m A cm-2,and FF of 65.7%.And corresponding devices with binary solvent additives showed a higher PCE of 11.2% with a Voc of 0.83 V,Jsc of 19.6 m A cm-2,and FF of 68.9% than that of the devices with single solvent additive treatment.In addition,when the optimal active layer was managed by 140 ? thermal annealing for 10 min,an optimal PCE of 11.5% has been achieved with a Voc of 0.81 V,Jsc of 20.8 m A cm-2,and FF of 68.4%.Finally,the morphology of active layers was optimized by the use of binary solvent additives.And performance of polymer solar cells has been improved by thermal annealing step to remove residual additives from the device.