title: Si solid-state quantum dot-based materials for tandem solar cells.
abstract: The concept of third-generation photovoltaics is to significantly increase device efficiencies whilst still using thin-film processes and abundant non-toxic materials. A strong potential approach is to fabricate tandem cells using thin-film deposition that can optimise collection of energy in a series of cells with decreasing band gap stacked on top of each other. Quantum dot materials, in which Si quantum dots (QDs) are embedded in a dielectric matrix, offer the potential to tune the effective band gap, through quantum confinement, and allow fabrication of optimised tandem solar cell devices in one growth run in a thin-film process. Such cells can be fabricated by sputtering of thin layers of silicon rich oxide sandwiched between a stoichiometric oxide that on annealing crystallise to form Si QDs of uniform and controllable size. For approximately 2-nm diameter QDs, these result in an effective band gap of 1.8 eV. Introduction of phosphorous or boron during the growth of the multilayers results in doping and a rectifying junction, which demonstrates photovoltaic behaviour with an open circuit voltage (VOC) of almost 500 mV. However, the doping behaviour of P and B in these QD materials is not well understood. A modified modulation doping model for the doping mechanisms in these materials is discussed which relies on doping of a sub-oxide region around the Si QDs.
authors.affiliation: ARC Photovoltaics Centre of Excellence, University of New South Wales, Sydney, NSW 2052, Australia. g.conibeer@unsw.edu.au.
authors.forename: Gavin
authors.initials: G
authors.lastname: Conibeer
authors.forename: Ivan
authors.initials: I
authors.lastname: Perez-Wurfl
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Hao
authors.forename: Dawei
authors.initials: D
authors.lastname: Di
authors.forename: Dong
authors.initials: D
authors.lastname: Lin