Construction And Characterization Of Non-fullerene Receptor Materials Based On Carbon-oxygen Bridge Core Units

Recently,organic solar cells?OSCs?have attracted interests from both academia and industry due to the advantages like lightweight,flexibility,semitransparency,and roll-to-roll production.since the LUMO level of the fullerene material can not controllable,the increase of the open circuit voltage(V_OC)in the cell is limited.In order to further improve the PCE of the cell,it is crucial to design and develop the new non-fullerene receptors?NFAs?.The carbon-bridged?C-bridged?ladder-type D unit plays a crucial role in developing high performance A–D-A NFAs.However,the medium electron-donating capability of C-bridged units is unfavorable for making NFAs with strong light-harvesting capability.Therefore,the development of a new D unit has great significance.Above problems,this paper designs and develops a series of high-efficiency NFA molecules based on C-O bridges.we investigated their optical,thermostability and electrochemical properties,charge transport and photovoltaic performance.The results are summarized as follows:1.A heptacyclic carbon-oxygen-bridged ladder-type unit,COi7,was designed.Two corresponding nonfullerene acceptors,CO_i7IC and CO_i7DFIC,were developed.The single crystal structure of COi7IC indicates an S-shaped backbone and a packing via?-?interaction of the end groups.Compared to CO_i7IC,CO_i7DFIC has a higher EQE response,and F atoms are introduced to make the band gap smaller.By fabricating the device with the polymer donor PTB7-Th,it was found in the exciton dissociation and bimolecular recombination tests that COi7DFIC can generate more effective charges with less recombination,and the device gave a power conversion efficiency of 6.36%and 8.32%,with a decent fill factor of 58.9%and 71.9%.2.Three nonfullerene acceptors CO5DFIC,CO5DFIC-OT and CO5DFIC-ST were design and developed.CO5DFIC-OT and CO5DFIC-ST have alkoxythiophene?OT?and alkylthiothiophene?ST??-bridges,respectively.The two acceptors,CO5DFIC-OT and CO5DFIC-ST,present higher LUMO levels and enhanced light-harvesting capability than CO5DFIC without?-bridges.The exciton dissociation efficiencies of CO5DFIC,CO5DFIC-OT and CO5DFIC-ST were 91.5%,87.5%and95.3%,respectively.The?h/?e of the mixed membrane were 1.8,9.1 and 6.7,and the?values were 0.996,0.959 and 0.986 in the bimolecular composite test.which was consistent with the EQE responsivity and FF change of the three molecules.CO5DFIC CO5DFIC-OT and CO5DFIC-ST obtained 5.58%,7.66%,and 9.73%PCE from PTB7-Th:NFA devices.