“…In particular, efficient light harvesting is an important issue, because ambient photon flux density is low in general. With this in mind, we have developed the following three new classes of nanomaterials and photoelectrochemical devices based on the nanomaterials: (1) photocatalysts with energy storage abilities, [1][2][3][4][5][6][7][8] which can store energy derived from light and continue redox reactions even in the night, (2) plasmonic metal nanoparticle ensembles stabilized by metal oxide nanomasks and ultrathin metal oxide coatings, 9,10 as well as solid-state photovoltaic cells 11 and plasmon resonance sensors 9,10,12 based on the ensembles, and (3) organic [13][14][15][16][17][18] or organic-inorganic hybrid [19][20][21] photoelectrodes with optimally arranged plasmonic metal nanoantennas. The former one stores surplus energy during the day and uses it in the night, while the latter two trap photons efficiently taking advantage of the large absorption cross-section of plasmonic metal nanoparticles.…”