Materials assembly and integration at multiple length scales are critical to the functioning of new generation solar energy devices, and call for basic science informed design and elaboration. The key is to understand and leverage the intrinsic properties of the tailored materials as well as the interplay between the material components so as to realize the desired functions.This contribution will present some of recent results in interfacing and assembling various nanostructures by solution processes. The novel materials have been explored as efficient light absorbers, carrier transporters, interlayers and surface reaction promotes for high-performance solar energy conversion device, particularly perovskites solar cells and photoelectrochemical cells. Implications of these results on the future development of new solar energy devices will be discussed.