Influence of the terminal electron donor in D–D–π–A phenothiazine dyes for dye-sensitized solar cells

•Three new D–D–π–A phenothiazine dyes were synthesized for DSSCs.•The terminal electron donor has distinct effects on light-harvesting and efficiency.•An efficiency of 7.13% was achieved for the WR8 sensitized cobalt cell.

We report three new molecularly engineered push–pull dyes based on phenothiazine (PTZ) as a π-conjugating linker and arylamine moiety as donor and compared with a simple phenothiazine derived reference dye. Absorption spectra, electrochemical cyclic voltammetry, theoretical calculations, current–voltage curves and electrochemical impedance spectroscopy were performed to understand the terminal electron donor influence on the performance of D–D–π–A PTZ dyes. Among these four dyes, the dye incorporating a 9-hexyl-9H-carbazole shows the best photovoltaic performance: a short-circuit photocurrent density of 14.02 mA cm−2, an open-circuit photovoltage of 748 mV, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 7.13% under standard global AM 1.5 solar light conditions.

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