Understanding the Role of Oxygen Vacancy in Visible–Near‐Infrared‐Light‐Absorbing Ferroelectric Perovskite Oxides Created by Off‐Stoichiometry

Abstract

Recently, the visible or even-to-near-infrared light absorbing perovskite ABO 3 solid state solutions, show promising application in solar cells and multienergy harvesters or sensors by simultaneously introducing transition metal and oxygen vacancies. However, the existence of oxygen vacancies fundamentally causes photoexcited carrier trapping and large leakage current. Therefore, it is still challenging to limit oxygen vacancies while maintaining low bandgap and high ferroelectricity. Here, an efficient charge compensation strategy by finely adjusting the ion ratio on the A-site to obtain an oxygen-vacancy-free relaxer ferroelectric is demonstrated in the system of Na x Bi y TiO 3 -BaTi 0.5 Ni 0.5 O 3 , where y > x. It is found that the oxygen-vacancyfree composition still yields strong visible-near-infrared-light-absorbing and enhanced photoresponse, in which the photocurrent density doubles from ≈0.16 to ≈0.32 μA cm −2 . A new bandgap tuning mechanism is proposed according to the local structural information of Ni ions obtained via extended X-ray absorption fine structure. Moreover, this work succeeds in establishing the relationship between the concentration of oxygen vacancies and ferroelectric/piezoelectric properties of Na x Bi y TiO 3 -BaTi 0.5 Ni 0.5 O 3 . This research points out a promising route to the material design of bandgap engineered ferroelectrics with controlled defects, which is expected to benefit a wide range of functional energy conversion devices.

Visible or Near-Infrared Light Self-Powered Photodetectors Based on Transparent Ferroelectric Ceramics

“…For example, Ni 2+ -doped FE [KNbO 3 ] 0.9 [BaNi 1/2 Nb 1/2 O 3−δ ] 0.1 has a direct band gap of 1.39 eV and a photocurrent density approximately 50 times larger than that of the former alternative . Similarly, the band gap engineering method above has been applied successfully in (Na 0.5 Bi 0.5 )­TiO 3 -based, , BaTiO 3 -based, BiFeO 3 -based, PbTiO 3 –based, and (K 0.5 Na 0.5 )­NbO 3 -based , FEs.…”

Boosting the Photocatalytic Ability of Bandgap Engineered (Na0.5Bi0.5)TiO3–BaTiO3 by N–Ni Codoping

“…With the doping of N 3– , the peak positions of the (100), (110), and (200) plane shift to the lower 2θ value (the detailed shift on these peaks is presented in Figure S1) since the radius of N 3– is larger than that of O 2– , indicating N 3– are successfully introduced into the lattice structure and increase the lattice size of Ni-doped NBT-BT. For Ni–N-codoped NBT-BT composition, Ni 2+ has been proved to substitute the Ti 4+ at center of oxygen octahedron in our early work . SEM/EDS is performed to analyze the composition of the ceramic powder, which is presented in Figure b.…”

Photoresponsive Piezoelectrics

“…The influence of N in the structure on piezoelectricity is yet to be examined. On the other hand, in order to eliminate the charge trapping effect caused by the oxygen vacancies in the structure, decreasing the ratio between Na + and Bi 3+ ions could balance the chemical valence and hence was able to reduce the concentration of oxygen vacancies while maintaining a high d 33 (166 pC/N compared to 151 pC/N for NBT-BTNO with higher oxygen vacancy concentration), as well as supporting a narrow band gap of 2.2 eV (Xiao et al, 2019b).…”