Organic dyes incorporating low-band-gap chromophores based on π-extended benzothiadiazole for dye-sensitized solar cells

A series of new π-conjugated organic dyes (HKK-BTZ1, HKK-BTZ2, HKK-BTZ3 and HKK-BTZ4), comprising triphenylamine (TPA) moieties as the electron donor and benzothiadiazole moieties as the electron acceptor/anchoring groups, was synthesized for the use in dye-sensitized solar cells (DSSCs). TPA units are bridged to benzothiadiazole with single(S), double(D) and triple bonds(T) in different derivatives. And HKK-BTZ1 was modified by introducing alkoxy group of TPA unit, because the bulky alkoxy group is a strong donating group for the more red shift and for reducing aggregation of dyes in TiO2 film. The structure-property relationship was investigated. Under standard global AM 1.5 G illumination, a maximum photo-to-electron conversion efficiency of 7.30% was achieved with the DSSC based on dye HKK-BTZ4 (JSC = 17.9 mA/cm−2, VOC = 0.62 V, FF = 0.66), while the Ru dye N719-sensitized DSSC showed an efficiency of 7.82% with a JSC of 17.5 mA/cm−2, a VOC of 0.62 V, and a FF of 0.72.

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► A series of new metal-free organic dyes, comprising triphenylamine moieties as the electron donor and benzothiadiazole moieties as the electron acceptor was designed and synthesized for the use in DSSC.
► Triphenylamine units are bridged to benzothiadiazole with single, double and triple bonds in different derivatives.
► HKK-BTZ4 was modified by introducing alkoxy group of triphenylamine donor unit.
► Under AM 1.5G illumination, a maximum conversion efficiency of 7.3% was achieved with the DSSC based on HKK-BTZ4 (JSC = 17.9 mA/cm−2, VOC = 0.62 V, FF = 66.2).