Browsing by Author "Lin, Chun-Yen"

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Photovoltaic conversion and quantum efficiency in perovskite multiferroic ceramics
(2018-05) Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Schmidt, V. Hugo; Chien, R. R.; Lin, Chun-Yen
Junction-driven photovoltaic effects in lead-free perovskite BiFeO3 multiferroic materials have demonstrated promising applications in energy harvesting and optical sensors. This study highlights remarkable photon-to-electron external quantum efficiency (EQE) of ∼9% and light-to-electric power-conversion efficiency (PCE) of ∼0.8% in the heterostructure consisting of A-site neodymium-doped BiFeO3 ceramic and indium-tin-oxide (ITO) thin film under irradiation of wavelength λ = 405 nm. A theoretical p-n-junction model based on the photo-generated carriers was employed to quantitatively describe open-circuit voltage (Voc) and short-circuit current density (Jsc) as functions of irradiation intensity, and to calculate junction widths and carrier densities. The direct band gap and the degree of local disorder (or defect state) were estimated using the photon-energy-dependent optical attenuation coefficient with the Tauc and Urbach relations.
Tailoring microstructure and photovoltaic effect in multiferroic Nd-substituted BiFeO3 ceramics by processing atmosphere modification
(2018-11) Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Lin, Chun-Yen; Schmidt, V. Hugo
This study highlights significant effects of processing atmosphere ratio (O2/N2) on microstructure, impurity phases, atomic hybridization, band gap, and photovoltaic properties in (Bi0.93Nd0.07)FeO3 (BFO7Nd) ceramics. A Rietveld-refinement analysis indicates increased oxygen and bismuth vacancies in the specimens processed in the O2-rich atmosphere (hereafter called O2-rich-atmosphere specimens). In the matrix containing mainly Fe3+ ions, Fe4+ cations were identified with O2 concentration decreasing in the atmosphere by Fe K/L-edges synchrotron X-ray absorption. Oxygen K-edge absorption reveals reduced hybridizations of the O 2p–Fe 3d and the O 2p–Bi 6sp orbitals in the O2-rich-atmosphere specimens. Photovoltaic effects in the ITO/BFO7Nd/Au heterostructures under near-ultraviolet irradiation (λ = 405 nm) exhibit strong dependences on O2/N2 ratio. A p-n-junction model was used to describe open-circuit voltage and short-circuit current density as functions of irradiation intensity. The calculated carrier densities (in BFO7Nd ceramics) and p-n-junction widths (in the dark) are ∼1023 m−3 and a few hundred nanometers, respectively.