Tin Quantum Dot Materials for Third Generation Photovoltaics: Optical Properties

  • Dr Shujuan Huang, ARC Photovoltaics Centre of Excellence, University of New South Wales, Australia
  • Dr Eun-Chel Cho, University of New South Wales, Australia
  • Gavin Conibeer, University of New South Wales, Australia
  • Y Huang, ARC Photovoltaics Centre of Excellence, University of New South Wales, Australia
  • Prof Martin Green, ARC Photovoltaics Centre of Excellence, University of New South Wales, Australia
  • Shuying Cheng, Department of Electronic Science and Applied Physics, Fuzhou University, China

    • Objective
    The tandem cell is one of the most promising approaches to breakthrough the conventional efficiency limit of photovoltaic cells [1]. In a tandem device, each cell has a different bandgap, and absorbs and converts a different part of the solar spectrum, more efficiently. Our group concentrates on all-silicon tandem cell based on engineering wider band gap materials using quantum confinement in Si nanocrystals. Recently we have extended this work to tin (Sn) because of the possibilities of low process temperatures and greater bandgap flexibility. This work aims to make Sn-based QD materials with controlled energy bandgap and to study the optical properties.

    Experimental methods
    The Sn-rich precursor layers were prepared by magnetron co-sputtering of Sn and dielectric materials such as SiO2 and were subsequently annealed in a vacuum chamber to precipitate Sn nanocrystals embedded in a matrix [2]. Sn QDs with very uniform size were fabricated by depositing multilayer structures of alternating Sn-rich SiO2 layer and SiO2 layer and then annealing at relatively low temperatures. We studied the optical absorption and photoluminescence (PL) of the Sn QD materials.

    Results and conclusion
    The formation of Sn nanocrystals with low temperature annealing at 400~600 °C was confirmed by TEM and XRD [2]. Sn oxide nanoclusters 2.5-5.0 nm in diameter were also observed by TEM. Sn-based films showed wide optical bandgap of about 4.2 eV, believed to be dominated by Sn oxide nanoclusters and oxygen-related defects formed in SiO2 matrix. In addition, the Sn QD samples showed strong violet PL at ~3.2 eV at room temperature. The detailed optical studies on the Sn-based QD samples will be presented and discussed.

    [1] M.A. Green, Third Generation Photovoltaics, Springer, 2003.
    [2] S. Hunag, et al. J. Appl. Phys. 102, 114304 (2007).