title: A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cells.
abstract: A novel "photovoltaics (PV) + electrolyzer" concept is presented using a simple, small, and completely stand-alone non-biased device for solar-driven overall water splitting. Three or four spherical-shaped p-n junction silicon balls were successfully connected in series, named "SPHELAR." SPHELAR possessed small projected areas of 0.20 (3PVs) and 0.26 cm(2) (4PVs) and exhibited working voltages sufficient for water electrolysis. Impacts of the configuration on the PV module performance were carefully analyzed, revealing that a drastic increase in the photocurrent (≈20%) was attained by the effective utilization of a reflective sheet. Separate investigations on the electrocatalyst performance showed that non-noble metal based materials with reasonably small sizes (<0.80 cm(2)) exhibited substantial currents at the PV working voltage. By combining the observations of the PV characteristics, light management and electrocatalyst performance, solar-driven overall water splitting was readily achieved, reaching solar-to-hydrogen efficiencies of 7.4% (3PVs) and 6.4% (4PVs).
authors.affiliation: Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kageshima
authors.affiliation: Division of Physical Science and Engineering, KAUST Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), 4700 KAUST, Thuwal, 23955-6900, Saudi Arabia.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Shinagawa
authors.affiliation: Kyosemi Corporation, 949-2 Ebisu-cho, Fushimi-ku, Kyoto, 612-8201, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Kuwata
authors.affiliation: Kyosemi Corporation, 949-2 Ebisu-cho, Fushimi-ku, Kyoto, 612-8201, Japan.
authors.forename: Josuke
authors.initials: J
authors.lastname: Nakata
authors.affiliation: Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Minegishi
authors.affiliation: Division of Physical Science and Engineering, KAUST Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), 4700 KAUST, Thuwal, 23955-6900, Saudi Arabia.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Takanabe
authors.affiliation: Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Domen