Synthesis, Characterization and Photovoltaic Properties of Truxene Based Star-Shaped Non-Fullerene Acceptors†

doi:10.7503/cjcu20180792

Abstract

Abstract:

Small molecular non-fullerene acceptors(NFAs) have recently drawn tremendous attention. In this work, a class of star-shaped NFAs, namely 2,2',2″-{[(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a：1',2'-c]fluorene-2,7,12-triyl)tris(thiophene-5,2-diyl)]tris(methanylylidene)}tris(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)trimalononitrile(NFT-C6) and 2,2',2″-{[(5,5,10,10,15,15-hexadecyl-10,15-dihydro-5H-diindeno[1,2-a：1',2'-c]fluorene-2,7,12-triyl)tris(thiophene-5,2-diyl)]tris(methanylylidene)}tris(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)trimalononitrile(NFT-C10), have been designed and synthesized by an alkyl-substituted truxene as the central group and three strong electron withdrawing cyano-1,3-indanone as the terminal groups. The highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) energy levels of the compounds both lies at -5.66 and -3.75 eV, respectively. The NFT-C6 and NFT-C10 films show intense absorption from 400 nm to 700 nm with a maximum at 606 and 586 nm, respectively. The polymer solar cells(PSCs) devices using (PBDB-T=poly{[(2,6-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2-b：4,5-b']dithiophene})-alt-{5,5-[1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c：4',5'-c']dithiophene-4,8-dione]})(PBDB-T) as a donor, and NFT-C6 or NFT-C10 as an acceptor have been fabricated, which shows a power conversion efficiency(PCE) of 1.09% and 5.23%, respectively. The external quantum efficiency(EQE) spectra indicated broad photocurrent response from 300 nm to 700 nm of the devices. The aggregation properties of the device have been investigated by atomic force microscopy(AFM). The height and phase images of the active layers indicated that the PBDB-T： NFT-C10 based film showed proper phase separation with dozens of nanometers, which was benefit to exciton dissociation and produced desired device performance. On the other hand, the low short-circuit current density, fill factor and PCE of the ITO/ZnO/PBDB-T：NFT-C6/MoO₃/Ag photovoltaic device was attributed to the overlarge phase separation size between the donor and the acceptor. These results demonstrated that truxene based star-shaped NFAs have promising application in PSCs devices.

Key words: Non-fullerene acceptor material, Donor-acceptor(D-A) structure, Truxene, Photovoltaic property

CLC Number:

O631
O646

TrendMD:

SONG Meining, HAO Haijing, CHEN Weiping, GU Fang, BA Xinwu. Synthesis, Characterization and Photovoltaic Properties of Truxene Based Star-Shaped Non-Fullerene Acceptors^†[J]. Chem. J. Chinese Universities, 2019, 40(7): 1527.

Figures/Tables 6

Scheme 1 Synthetic routes of NFT-C6 and NFT-C10

Fig.1 UV-Vis absorption spectra of NFT-C6(a, c) and NFT-C10(b, d) in solutions(a, b) and films(c, d) and PBDB-T film(e)

Fig.2 DFT calculated HOMO/LUMO energy levels and orbital distributions of NFT-C6(A) and cyclic voltammograms curves(B) of NFT-C6(a) and NFT-C10(b) in 1×10-5 mol/L solution of CH2Cl2(A) The hexyl groups were simplified as methyl groups during the calculation.

Table 1 Photophysical and electrochemical properties of NFT-C6 and NFT-C10

Compound	$λ abs Solution$ /nm	ε_solution/(L·cm^-1·mol^-1)	$λ abs Film$ /nm	$E g Film$ /eV	HOMO/eV	LUMO/eV
NFT-C6	564	1.82×10⁵	586	1.78	-5.66	-5.66
NFT-C10	564	2.13×10⁵	606	1.86	-3.75	-3.75

Table 1 Photophysical and electrochemical properties of NFT-C6 and NFT-C10

Compound	$λ abs Solution$ /nm	ε_solution/(L·cm^-1·mol^-1)	$λ abs Film$ /nm	$E g Film$ /eV	HOMO/eV	LUMO/eV
NFT-C6	564	1.82×10⁵	586	1.78	-5.66	-5.66
NFT-C10	564	2.13×10⁵	606	1.86	-3.75	-3.75

Fig.3 J-V(A) and EQE(B) curves of PBDB-T：NFT-C6 and PBDB-T：NFT-C10 photovoltaic devicesa. NFT-C6; b. NFT-C10

Fig.4 AFM height(A, C) and phase(B, D) images of PBDB-T：NFT-C6(A, B) and PBDB-T：NFT-C10(C, D) photovoltaic devices

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