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Band-gap tunable thiadiazolo[3,4-g]quinoxaline derivatives as non-fullerene acceptors in organic photovoltaic cells processed from low toxic ethanol/anisole mixtures

Costa, C. ; Farinhas, J. ; Velho, M. ; Avó, João Avó ; Matos, M. ; Galvão, A. ; Charas, A.

New Journal of Chemistry Vol. 43, Nº 36, pp. 14246 - 14256, August, 2019.

ISSN (print): 1144-0546
ISSN (online): 1369-9261

Journal Impact Factor: 3,086 (in 2014)

Digital Object Identifier: 10.1039/c9nj02419k

The synthesis, characterisation and application as electron-acceptors in organic photovoltaic cells of
new [1,2,5]thiadiazolo[3,4-g]quinoxaline-based small molecules with oligo(ethylene oxide) solubilising
groups and tunable optical bandgaps are reported. A new p-type polymer consisting of a polythiophene
derivative substituted with analogous solubilising groups was also synthesised to perform as a donor, in
combination with the small molecules, for bulk-heterojunction solar cells using ethanol/anisole mixtures
as low toxic solvents to process the active blends. Comparison of the structural, electrochemical and
photophysical properties of the small molecules elucidated on the structural dependence of their optical
bandgaps, ranging from 1.31 to 2.25 eV. The active layers composed of the polythiophene donor and
the small molecules showed well-intermixed morphologies, and the best performing blends showed a
fibrillar-type morphology, indicative of more ordered molecular packings. Blends processed from the
50 : 50 (v/v) mixture of ethanol and a low toxic solvent, anisole, yielded low power conversion
efficiencies of 0.39% in non-optimized organic solar cells. Although the efficiencies are low, these are
the first reported results of OSCs with active layers composed of non-fullerene acceptors processed
from ethanol-based solvent formulations. This study provides guidelines for the design of non-fullerene
acceptors for the fabrication of OSCs processed from environmentally friendly solvents