Study On The Design And Photovoltaic Properties Of Non-fullerene Acceptors Based On Ladder-type Heterocycle

Solution-processing Organic solar cells(OSCs)adopting bulk-heterojunction(BHJ)structure have attracted increasing interest over the past few decades from both academic and industry,due to their significant advantages in terms of easy processing,low cost,flexibility and semitransparency.Especially,non-fullerene acceptors used in OSCs have recently drawn vigorous attention because of the features of their tunable energy levels,strong absorption in the visible and even near-infrared region(Vis-NIR)and easy purification.In this dissertation,several series of acceptor-donor-acceptor(A-D-A)type non-fullerene acceptors(NFAs)have been synthesized,with their optical and electrochemical properties,charge transport and photovoltaic properties systematically investigated.The main contents are summarized as follows.In Chapter 2,two isomers were observed in synthesis of A unit with asymmetric thiophene structure.An experimental-theoretical correlation study reveals the isomer having lower total energy as the major component.The structurally defined A unit generates the thiophene-ending ITIC-type NFAs(ITCT)as a good match for PTB7-Th.The resulted PTB7-Th/ITCT blends based devices give an appreciable power conversion efficiency(PCE)of 8.23%and a relatively high open-circuit voltage(Voc)of 0.96 V without any optimization.Upon device processing with thermal annealing and the addition of 0.1%1,8-diiodooctane(DIO),the active layer achieves more ordered and crystalline morphology.Consequently,a high PCE of 10.42%has been revealed with a Voc of 0.95 V,a short circuit current(JSC)of 15.13 mA· cm-2 and a high fill factor(FF)of 0.72.In Chapter 3,a new electron-rich central building block,5,5,12,12-tetrakis-(4-hexylphenyl)-indacenobis-(dithieno[3,2-b:2',3'-d]pyrrol)(INP)has been designed.And two derivatized NFAs(INPIC and INPIC-4F)end-capped with 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile(IC)or fluorinated IC by Knoevenagel condensation reaction have been constructed and systematically characterized.These two molecules reveal broad(600-900 nm)and strong absorption due to the satisfactorily electron-donating ability of INP.Compared with its counterpart INPIC,fluorinated non-fullerene acceptor INPIC-4F exhibits a stronger near-infrared absorption with narrower optical bandgap of 1.39 eV,an improved crystallinity with higher electron mobility and down-shifted highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)energy levels.The organic solar cells based on INPIC-4F exhibit a high power conversion efficiency of 13.13%and a relatively low energy loss(Eloss)of 0.54 eV,which is among the highest efficiency record for binary OSCs in the literature.In Chapter 4,two new non-fullerene acceptors were designed by introducing alkoxy groups to indacenodithiophene(IDT)core.The key intermediate D unit was constructed via several procedures,i.e.,stannylation,Stille coupling,and Friedel-Crafts intramolecular cyclization.The effects of alkoxy side chain on optical and electrochemical properties were investigated.IDTO-IC and IDTO-IC-4F exhibit worse solubility and enhanced crystallization properties for noncovalent interaction.Consequently,the as-cast OSCs deliver the highest PCE of 2.28%with low Jsc and FF.