Effect of electron donor groups on the performance of benzothiadiazole dyes with simple structures for dye-sensitized solar cells

Three structurally simple metal-free organic dyes (C1, C2 and C3) with D-A-pi-A structure, having benzothiadiazole auxiliary acceptor, benzene pi-bridge and cyanoacrylic acid anchoring group, were designed and synthesized for use in dye-sensitized solar cells (DSSCs). Diphenylamine, carbazole and phenothiazine were used as electron donor groups and their effects on the photovoltaic performance were investigated. It was found that C1 dye with diphenylamine donor has the longest maximum absorption wavelength and highest molar extinction coefficient, which is benefical for harvesting more photons and generating a higher photocurrent. Therefore, the DSSC based on C1 dye gives a power conversion efficiency (PCE) of 5.01 %, which is greater than those of C2 dye with carbazole donor (3.51 %) and C3 dye with phenothiazine donor (1.76 %). Finally, the co-sensitization of C1 and C2 exhibits a highest PCE of 5.49 % may be due to broader visible light absorption.