Abstract
Remarkably enhanced photovoltaic effects have been observed in the heterostructures of p-type A-site Nd3+-doped BiFeO3 (Bi0.9375Nd0.0625)FeO3 (or BFONd) polycrystalline ceramics and the n-type ITO thin film. The maximum power conversion is ~0.82%, which is larger than 0.015% in BiFeO3 (BFO) under blue-ultraviolet irradiation of wavelength λ = 405 nm. The current-voltage (I-V) characteristic curve suggests a p-n junction interface between the ITO thin film and BFO (or BFONd) ceramics. The band gaps calculated from first-principles for BFO and BFONd are respectively 2.25 eV and 2.23 eV, which are consistent with the experimental direct band gaps of 2.24 eV and 2.20 eV measured by optical transmission spectra. The reduction of the band gap in BFONd can be explained by the lower electronic Fermi level due to acceptor states revealed by first-principles calculations. The optical calculations show a larger absorption coefficient in BFONd than in BFO.
Highlights
Multiferroic BiFeO3 (BFO) possesses a ferroelectric Curie temperature of Tc ~ 1103 K and a G-type antiferromagnetic order (Neel temperature TN ~ 6 43 K) with a spatially modulated spin structure
The density-functional-theory (DFT) calculation and X-ray absorption spectroscopy revealed that the A-site rare-earth lanthanum (La) doping in BFO can reduce the leakage current[18]
It has been reported that doping can be one of the most effective methods used to improve ferroelectric and magnetic properties[19,20,21,22], as the Bi-site substitution can effectively control the volatility of Bi atoms with reduction of oxygen vacancies[23] and enhancement of photovoltaic effects[24,25,26]
Summary
The optical band gap depends strongly on the proper choice of the Hubbard parameter U for Fe41. The ITO/BFONd/Au heterostructure has demonstrated comparable photovoltaic effects, including open-circuit voltage (Voc), short-circuit current density (Jsc), and power-conversion efficiency (η). Where w is ceramic thickness, B is the radiative recombination factor which is temperature-dependent[50], q is carrier charge, T is room temperature (300 K), k is the Boltzmann constant, and Nc and Nv are effective densities of states in the conduction and valence bands. (One Nd atom contributes 6 more valence electrons than the Bi atom in BFO.) Fig. S3(a) shows the open-circuit voltage Voc and short-circuit current density (Jsc) as functions of irradiation intensity from the ITO/BFO/Au and ITO/BFONd/Au heterostructures under irradiation for the same thickness of d = 0.2 mm. We used Eq (3) to estimate the Jph ratio between BFO and BFONd, i.e
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