Photocurrent enhancement of hemicyanine dyes containing RSO3- group through treating TiO2 films with hydrochloric acid

Two kinds of hemicyanine dyes, 2-[4-(dimethylamino)styryl]benzothiazolium propylsulfonate (BTS) and 2-[4(dimethylamino)styryl]-3.3-dimethylindolium propylsulfonate (IDS), were synthesized and characterized with respect to their UV-vis, fluorescence, and redox properties. Both dyes show outstanding properties for charge transfer on HCl-treated nanocrystalline TiO2 films with near 100% incident monochromatic photon-to-electron conversion efficiency (IPCE) at the maximum absorption wavelength. This treatment was found to improve short-circuit photocurrent significantly. with increases by 99% and 329% for BTS and IDS, respectively. Overall yields were hence improved remarkably as a result of photocurrent enhancement: BTS increased by 66% from 3.1% to 5.1% and IDS increased by 260% from 1.3% to 4.8%. This phenomenon can be explained by the positive shift of flat band potential for TiO2 and the increased amount of adsorbed dye molecules upon HCl treatment. The values for IPCE. short-circuit photocurrent, and overall solar energy to electricity conversion efficiency are all among the highest values respectively in the pure organic sensitizers reported so far.