Mesoporous structures show intriguing properties in the field of energy conversion. The nanoscale morphology of porous, semiconducting metal oxides has a profound impact on their physical properties, including charge transport, ion intercalation and redox catalysis. We will discuss several strategies for the formation of hierarchical porous oxide semiconductor systems, which are partially based on fusing pre-formed oxide nanocrystals in the presence of appropriate porogens. These systems are employed as efficient active layers in photovoltaic cells and for electrochemical energy storage, respectively. We will discuss the significant impact of the nanoscale morphologies of these self-assembled materials on their transport properties.