Effect of structural modification on the performances of phenothiazine-dye sensitized solar cells

• Three novel phenothiazine-based dyes were synthesized for DSSCs.
• The DSSC device based on the dye DX1 obtained the highest PCE of 5.69%.
• The dyes DX2 and DX3 displayed broad spectra responses.

Three novel dyes DX1, DX2 and DX3 containing phenothiazine are designed and synthesized for dye-sensitized solar cells (DSSCs). Photophysical, electrochemical and photovoltaic properties of the three dyes have been systematically investigated. The results show that the DX1-based DSSC with 0.5 mM chenodeoxycholic acid (CDCA) obtains the power conversion efficiency (PCE) of 5.69%. When an additional electron-deficient benzothiadiazole (BT) unit is introduced into the molecular structures of the dyes DX2 and DX3, the absorption spectra are broadened. But the short-circuit photocurrent density (Jsc) of the devices are decreased due to the blocked electron transfer, so the DSSC device based on DX2 only obtains the PCE of 3.43%. Furthermore, a triphenylamine (TPA) unit with high electron-donating ability is joined onto the nitrogen atom of phenothiazine donor in DX3, which enhances the electron injection efficiency and reduces the dye aggregation. Thus, the Jsc is improved, resulting in a higher PCE of 4.41% in the DX3-based dye than the DX2-based one.

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