Photoelectrochemical properties and interfacial charge transfer kinetics of BODIPY-sensitized TiO2 electrodes

We present studies of the photoelectrochemical characteristics and interfacial charge transfer dynamics of two (4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene) BODIPY dyes (BODIPY-1 and 2) attached to nanostructured TiO2 electrodes. BODIPY-1 bears two carboxylic acid groups at its 2 and 6 positions and BODIPY-2 is modified with two cyanoacetic acid groups at these positions. Photoelectrochemistry measurements show that BODIPY-2 has better photostability and device short-circuit current density than BODIPY-1 because of its broader light absorption and efficient charge injection as shown by ultrafast transient absorption spectroscopy and steady-state photoelectrochemical studies. The more efficient photocurrent generation by BODIPY-2 is also attributed to the improved redox reaction kinetics with its hole transport media, I-/I-3(-), in comparison with BODIPY-1.