Enlarging the molecular size of zinc phthalocyanine (Pc) dyes three dimensionally with 2,6-diphenylphenoxy substituents significantly reduced the aggregation of the dyes on a TiO2 surface. As a result, the incident photon-to-current conversion efficiency was improved not only in the Q band but over the whole absorption range, achieving 4.6% energy conversion efficiency under one-sun conditions. Electron Lifetime measurements indicated that these Pc dyes do not enhance charge recombination, encouraging further development of Pc.