Synthesis of diphenylamino-carbazole substituted BODIPY dyes and their photovoltaic performance in dye-sensitized solar cells

Non-alkylated BODIPY dye YHO-1 and hexa-alkylated BODIPY dye YHO-2, which have a diphenylamino-carbazole moiety as an electron-donating group at the 8-position on the BODIPY core and a carboxyhexyl group as an anchoring group on the carbazole ring, were designed and developed as photosensitizers for dye-sensitized solar cells (DSSCs). From the molecular structures of YHO-1 and YHO-2, when the two dyes were adsorbed on the TiO2 surface, it is assumed that the BODIPY core is located in close proximity to the TiO2 surface. The dye YHO-2 (Φf = 0.62) exhibits a significantly higher fluorescence quantum yield (Φf) than YHO-1 (Φf = 0.06). The short-circuit photocurrent density (Jsc) and solar energy-to-electricity conversion yield (η) for a DSSC based on YHO-2 are greater than those of YHO-1. This work demonstrates that fluorescent BODIPY dyes can inject electrons efficiently from the BODIPY core to the conduction band (CB) of the TiO2 electrode, but non-fluorescent BODIPY dyes result in lowering of photocurrent generation due to radiationless relaxation of the photoexcited dye.