The effect of conjugated groups for favourable molecular planarity and efficient suppression of charge recombination simultaneously of phenothiazine-based organic dyes for dye-sensitized solar cells

With the view to the poor coexistence between promoting molecular planarity towards improving the intramolecular charge transfer (ICT) effect and preventing charge recombination for dyes in Dye-sensitized solar cells (DSSCs). A novel 2-phenothiazine-amine-based organic dye PTZ-10 is synthesized and applied in DSSCs. The extra benzene and ethynyl conjugated groups are inserted as the isolation groups between the 2-phenothiazine-amine donor and benzothiadiazole auxiliary acceptor to obtain PTZ-17 in order to probe the possibility of reaching the aim of suppressing the charge recombination and strengthening molecular planarity synchronously in a better degree. Our photophysical measurement, electrochemical test and theoretical calculation demonstrate that the introduction of ethynyl and benzene is beneficial to the improvement of ICT effect and the inhibition of charge recombination, which can also be confirmed by the photovoltaic property and EIS study. Therefore, higher short-circuit photocurrent density ( J sc ) and the open-circuit voltage ( V oc ) are exhibited in devices based on PTZ-17 , along with the higher photoelectric conversion efficiency (PCE) up to 4.24 % relative to that of 3.37 % in PTZ-10. We demonstrated that the incorporation of different sizes of conjugated groups is a promising candidate to fine-tune the structure-performance of dye molecules in the development of DSSCs’ materials. • Two novel dyes PTZ-10 and PTZ-17 with 2-phenothiazine-amine as donor unit has been synthesized and utilized for DSSCs. • The effect of extra benzene and ethynyl groups on the performance of these two dyes was investigated. • The balance between promoting molecular planarity towards improving the ICT and preventing charge recombination was achieved.