The Design,Synthesis And Device Performance Characterization Of Non-Fullerene Fused-Ring Electron Acceptor Materials

In recent years,organic solar cells(OSCs)have attracted great attention in the field of organic photovoltaics due to unique advantages,such as light-weight,flexible preparation,and low-cost solution fabrication.The power conversion efficiency(PCE)is one of the important parameters to evaluate the photovoltaic performance of OSCs.In order to realize commercialization of OSCs,much work has focused on the promotion of PCE.The design of highly efficient organic photovoltaic materials is the key to improve the photovoltaic performance of OSCs,so that the understanding of the relationship between the molecular structure and photovoltaic performance can scientifically guide the design of highly efficient organic photovoltaic materials.In this paper,we designed and synthesized two different systems of non-fullerene fused-ring electron acceptor(NF-FREAs)materials and studied the relationship between photovoltaic performance and molecular structure and blend morphology by preparing OSCs.The" main research results are as follows1.By introducting the alkylthio substituent into the ?-bridge and fluorine atoms into the electron-withdrawing end group,a new NF-FREAs material ACS8 based on indacenodithiophene(IDT)as core,alkylthiothiophene as ?-bridge and electron-withdrawing 3-(1.1-dicyanomethylene)-5,6-diuoro-l-indanone(IC2F)as the end groups has been designed and synthesized.The introduction of alkylthio substituent and fluorine atoms expand the absorption spectrum and enhance the charge transfer,so ACS8 exhibits a narrower optical bandgap of 1.3 eV and a high electron mobility of 2.65×104 cm2 V-1 s-1.The device based on PTB7-Th:ACS8(1:2,w/w)with 0.5%PN(1-phenylnaphthalene)exhibited an optimal PCE of 13.2%with a Jsc of 25.3 mA cm-2.This PCE is among the highest values reported in the literature to date for PSCs based on ultra-narrow bandgap acceptors(Egopt?1,3 eV).2.By introducting benzo[1,2-b:4,5-b']difuran(BDF)unit into central aromatic fused rings and different fluorine atoms into the electron-withdrawing end group,the series of NF-FREAs materials IFIC1,IFIC2 and IFIC3 based on BDF as core,electron-withdrawing 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile(IC),2-((5)6-fluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile(IC-F),and IC-2F as the end groups have been designed and synthesized,respectively.The introduction of BDF unit and fluorine atoms broaden the absorption spectrum and enhance intramolecular charge transport,so the series of NF-FREAs materials IFIC1,IFIC2 and IFIC3 exhibit narrow optical bandgaps(1.49-1.44 eV)and high electron mobilities(2.72×10-4?6.2×10-4 cm2 V-1 s-1).As the number of fluorine atoms increases,the Egopt and ?e of NF-FREAs materials are reduced and enhanced,respectively.The devices based on PM6:IFIC1/PM6:IFIC2/PM6:IFIC3(1:1.5,w/w)with 0.75%PN and thermal annealing treatment at 120? for 20 min exhibited optimal PCEs of 8.65%,11.63%and 13.43%,respectively.The results indicate that the fluorination on the terminal groups of NF-FREAs materials can effectively improve the photovoltaic performance of OSCs.