Header menu link for other important links
X
Oxygen vacancy induced photoconductivity enhancement in Bi 1-x Ca x FeO 3-δ nanoparticle ceramics: A combined experimental and theoretical study
Subhajit Nandy, Kulwinder Kaur, Pavana S.V. Mocherla, ,
Published in American Institute of Physics Inc.
2018
Volume: 124
   
Issue: 19
Abstract
Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (O V ) leads to large scale enhancement of photoconductivity in BiFeO 3 (BFO). The O V concentration is increased by substituting an aliovalent cation Ca 2+ at Bi 3+ sites in the BFO structure. Furthermore, the O V concentration at the disordered grain boundaries can be increased by reducing the particle size. Photoconductivity studies carried out on spark plasma sintered Bi 1-x Ca x FeO 3-δ ceramics show four orders of enhancement for x = 0.1. Temperature dependent Nyquist plots depict a clear decrease in impedance with increasing Ca 2+ concentration which signifies the role of O V . A significant reduction in photoconductivity by 2 to 4 orders and a large increase in impedance of the air-annealed (AA) nanocrystalline ceramics suggest that O V at the grain boundaries primarily control the photocurrent. In fact, activation energy for AA samples (0.5 to 1.4 eV) is larger than the as-prepared (AP) samples (0.1 to 0.5 eV). Therefore, the room temperature J-V characteristics under 1 sun illumination show 2-4 orders more current density for AP samples. Density-functional calculations reveal that, while the defect states due to bulk O V are nearly flat, degenerate, and discrete, the defect states due to surface O V are non-degenerate and interact with the surface dangling states to become dispersive. With large vacancy concentration, they form a defect band that enables a continuous transition of charge carriers leading to significant enhancement in the photoconductivity. These studies reveal the importance of tailoring the microstructural features as well as the composition-tailored properties to achieve large short circuit current in perovskite oxide based solar cells. © 2018 Author(s).
About the journal
JournalData powered by TypesetJournal of Applied Physics
PublisherData powered by TypesetAmerican Institute of Physics Inc.
ISSN00218979
Open AccessNo
Concepts (20)
  •  related image
    Activation energy
  •  related image
    Binary alloys
  •  related image
    Ceramic materials
  •  related image
    Grain boundaries
  •  related image
    Microstructural evolution
  •  related image
    Nanocrystals
  •  related image
    Nanoparticles
  •  related image
    Particle size
  •  related image
    Perovskite
  •  related image
    Perovskite solar cells
  •  related image
    Photoconductivity
  •  related image
    CONTINUOUS TRANSITIONS
  •  related image
    Density-functional study
  •  related image
    J-v characteristics
  •  related image
    Microstructural features
  •  related image
    Nanocrystalline ceramics
  •  related image
    TAILORED PROPERTIES
  •  related image
    Temperature dependent
  •  related image
    VACANCY CONCENTRATION
  •  related image
    Oxygen vacancies