Dopant free, solar active ZnO photocatalysts with oxygen vacancy richness were achieved by a solution processing strategy followed by calcination at various temperatures 300, 500, 700, 800, and 900 degrees C. All the ZnO nanocrystals possessed defective structures with copious surface oxygen vacancies directed toward notable visible light absorption around lambda = 480 nm (band gap = 3.053.09 eV). The photocatalytic efficiencies of all ZnO samples were systematically examined under sunlight and UV illumination using methylene blue (MB) as a model system. ZnO calcined at 500 and 700 degrees C demonstrated microrod morphology with band gap energies of 3.08 and 3.09 eV respectively have shown the highest solar photocatalytic activity revealed the synergistic effect between oxygen vacancy and the rod morphology. ZnO calcined at 500 degrees C, having maximum surface oxygen vacancy sites degraded MB within 10 min whereas the commercial photocatalyst Degussa-P25 has taken 20 min under solar illumination.