Solvent vapor annealing (SVA) is one route to prepare block copolymer (BCP) thin films with long-range lateral ordering. The lattice defects in the spin-coated BCP thin film can be effectively and rapidly reduced using SVA. The solvent evaporation after annealing was shown to have a significant impact on the in-plane ordering of BCP microdomains. However, the effect of solvent evaporation on the out-of-plane defects in BCPs has not been considered. Using grazing-incidence x-ray scattering, the morphology evolution of lamellae-forming poly(2-vinlypyridine)-b-polystyrene-b-poly(2vinylpyridine) triblock copolymers, having lamellar microdomains oriented normal to substrate surface during SVA, was studied in this work. A micelle to lamellae transformation was observed during solvent uptake. The influence of solvent swelling ratio and solvent removal rate on both the in-plane and out-of-plane defect density was studied. It shows that there is a trade-off between the in-plane and out-of-plane defect densities during solvent evaporation. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 980-989