Alkyl-thiophene Functionalized D-π-A Porphyrins for Mesoscopic Solar Cells

An alkyl-thiophene functionalized D-π-A porphyrin (LW16) is designed and synthesized for dye-sensitized solar cells (DSSCs). Two hexyl-thiophene groups are attached to the meta-position of each meso-phenyl with a motivation to increase the light-harvesting ability as well as retarding the aggregation of porphyrins dyes. For comparison, none-alkyl substituted (LW14) and octyloxy substituted (LW15) porphyrin dyes are also synthesized to fully investigate the influence of porphyrin chromophore modification. These porphyrins present similar spectrum while the oxidation potentials vary as the functionalized group changes from the meta-position to ortho-position. The DSSCs based on the alkyl-thiophene functionalized (LW16), none-alkyl substituted (LW14), and octyloxy substituted (LW15) porphyrins can be achieved a power conversion efficiency of 8.5%, 6.9%, and 8.2% using I-/I3-redox electrolyte under full sunlight irradiation (AM 1.5 G, 100 mW cm−2), respectively. It is found that by tailoring the porphyrin chromophore with hexyl-thiophenes, the photocurrent of the corresponding devices could be increased without sacrifice the photovoltage. Detailed investigation, including spectroscopy, electrochemical and transient photovoltage decay measurement, provides general influence of π-conjugation extension at the meso-position onto the optoelectronic features of porphyrins dyes.