This study investigates the growth behavior of atomic-layer-deposited (ALD) Al2O3 overlayers on porous TiO2 electrodes, which comprise an anatase nanoparticle layer and a rutile particle layer, for optimizing dye-sensitized solar cells. The growth mode of the AID Al2O3 overlayers changes from island growth to layer-by-layer growth during the first few MD reaction cycles, and the growth mode transition is much more pronounced for the anatase electrode layer. The transition is likely a result of the reduction in the contractive lattice strain of the TiO2 nanoparticles. The lattice strain in the hydroxylated TiO2 nanoparticles is progressively reduced during the ALD Al2O3 deposition, resulting in the growth mode transition. (c) 2011 Elsevier B.V. All rights reserved.