Browsing by Author "Wei, H.-H."

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Enhanced photovoltaic effects in A-site samarium doped BiFeO 3 ceramics: The roles of domain structure and electronic state
(2015) Tu, Chi-Shun; Chen, Cheng-Sao; Chen, Pin-Yi; Wei, H.-H.; Schmidt, V. Hugo; Lin, C.-Y.; Anthoniappen, J.; Lee, J.-M.
This work reports enhanced photovoltaic (PV) responses of (Bi1 − xSmx)FeO3 (x = 0.0, 0.05, 0.10) ceramics (BFO100xSm) with ITO film under near-ultraviolet irradiation (λ = 405 nm). The ceramics were characterized by micro-Raman scattering, high-resolution transmission electron microscopy, and synchrotron X-ray absorption spectroscopy (XAS). A rhombohedral R3c symmetry with tilted FeO6 octahedra has been confirmed. The Fe K-edge absorption spectra reveal a slight shift toward higher energy as A-site Sm3+ substitution increases. The oxygen K-edge XAS reveals an enhancement of hybridization between the O 2p and unoccupied Fe 3d states due to Sm doping. The optical band gaps are in the range of 2.15–2.24 eV. The maximal PV power-conversion and external quantum efficiencies respectively reach 0.37% and 4.1% in the ITO/BFO5Sm/Au heterostructure. The PV responses can be described quantitatively by a p-n-junction-like model. The domain structures and hybridization between the O 2p and Fe 3d states play important roles for the PV responses.
Raman vibrations and photovoltaic conversion in rare earth doped (Bi 0.93 RE 0.07 )FeO 3 (RE=Dy, Gd, Eu, Sm) ceramics
(2016-01) Chang, L.-Y.; Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Schmidt, V. Hugo; Wei, H.-H.; Huang, D.-J.; Chan, T.-S.
High-resolution Raman spectra, X-ray diffraction, oxygen vacancies, synchrotron X-ray absorption spectroscopy, magnetization, optical band gap, and photovoltaic (PV) conversion have been studied in BiFeO3 (BFO) and (Bi0.93RE0.07)FeO3 (RE=Dy, Gd, Eu and Sm) multiferroic ceramics (7%Dy–BFO, 7%Gd–BFO, 7%Eu–BFO, and 7%Sm–BFO). 7%Dy–BFO exhibits a weak ferromagnetic behavior instead of the linear antiferromagnetic responses found in the other compounds. Optical transmissions reveal band gaps of 2.20–2.21 eV, which are slightly smaller than 2.24 eV in pure BFO. The current vs. voltage (I–V) characteristic curves of indium tin oxide (ITO)/(Bi0.93RE0.07)FeO3 ceramics/Au heterostructures suggest a p–n-junction-like behavior. The maximal PV power-conversion efficiencies under illumination of λ=405 nm in ITO/7%Dy–BFO/Au, ITO/7%Gd–BFO/Au, ITO/7%Eu–BFO/Au, and ITO/7%Sm–BFO/Au respectively reach 0.22%, 0.35%, 0.27%, and 0.24%, which are much larger than 0.017% in ITO/BFO/Au. The PV open-circuit voltage and short-circuit current can be reasonably described by a junction model as a function of illumination intensity.