title: Energetic alignment in nontoxic SnS quantum dot-sensitized solar cell employing spiro-OMeTAD as the solid-state electrolyte.
abstract: An environmentally friendly solid-state quantum dot sensitized solar cell (ss-QDSSC) was prepared by combining colloidal SnS QDs as the sensitizer and organic hole scavenger spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) as the solid-state electrolyte, and the energy alignment of SnS and TiO2was investigated. The bandgap of colloidal SnS QDs increased with decreasing particle size from 14 to 4 nm due to an upshift of the conduction band and a downshift of the valence band. In TiO2/SnS heterojunctions, the conduction band minimum (CBM) difference between TiO2and SnS was as large as ∼0.8 eV; this difference decreased with decreasing particle size, but was sufficient for electron injection from SnS nanoparticles of any size into TiO2. Meanwhile, the sensitizer regeneration driving force, that is, the difference between the valence band maximum (VBM) of SnS and the work function of the electrolyte, showed an opposite behaviour with the SnS size due to a downward shift of the SnS VB. Consequently, smaller SnS QDs should result in a more efficient charge transfer in heterojunctions, revealing the advantages of QDs vs larger particles as sensitizers. This prediction was confirmed by the improved photovoltaic performance of ss-QDSSCs modified with SnS nanoparticles, which peaked for 5-6 nm sized SnS nanoparticles due to the balance between electron injection and sunlight absorption.
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China; Department of Physical Electronics, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, Japan; These authors contributed equally.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Oda
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China; These authors contributed equally.
authors.forename: Heping
authors.initials: H
authors.lastname: Shen
authors.affiliation: Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China; College of Materials Science and Chemical Engineering, Hainan University, Haikou 570228, People's Republic of China.
authors.forename: Jianbao
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Physical Electronics, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, Japan.
authors.forename: Mitsumasa
authors.initials: M
authors.lastname: Iwamoto
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Lin
keywords: energy alignment; non-toxic; quantum dots; solar cell; solid-state