Light scattering of neighboring TiO2 particles in nanocrystalline films penetrated by electrolytes is examined based on rigorous solutions of the T-matrix method. Scattering efficiencies are improved by agglomeration of much larger particles than the nanocrystalline particles. A cluster of relatively small particles among the large particles effectively scatters every incident light because of symmetrical scattering. On the other hand, the improvement of scattering efficiencies with clusters of particles as large as the maximum efficiency is ascribed to significant forward scattering.