Manipulation of Oxygen Vacancy for High Photovoltaic Output in Bismuth Ferrite Films

Abstract

Very recently, the ferroelectric photovoltaic property of bismuth ferrite (BiFeO3, BFO) has attracted much attention. However, the physical mechanisms for its anomalous photovoltaic effect and switchable photovoltaic effect are still largely unclear. Herein, a novel design was proposed to realize a high photovoltaic output in BiFeO3 films by manipulating its oxygen vacancy concentration through the alteration of the Bi content. Subsequent results and analysis manifested that the highest photovoltaic output was achieved in Bi1.05FeO3 films, differing 1000 times from that of Bi0.95FeO3 films. Simultaneously, the origin of photovoltaic effect in all BiFeO3 films was suggested as the bulk photovoltaic mechanism instead of the Schottky effect. Moreover, oxygen vacancy migration should be the dominant factor determining the switchable photovoltaic effect rather than the ferroelectric polarization. A switchable Schottky-to-Ohmic interfacial contact model was proposed to illustrate the observed switchable photovoltaic or diodelike effect. Therefore, the present work may open a new way to realize the high power output and controllable photovoltaic switching behavior for the photovoltaic applications of BiFeO3 compounds.

XPS Study in BiFeO3 Surface Modified by Argon Etching

“…Figure 6a exhibits Bi 4 f at 0 s, with doublets peak around 158.7 and 164.2 eV corresponding an oxidation state Bi 3+ . These values agree with other BFO works [13,35], and they are close to bismuth oxide Bi 2 O 3 [36,37]. A peak related to metallic bismuth does not appear (just like in Bi 5d at 0 s) confirming that deposition in a low argon atmosphere is not enough to produce metallic species.…”

Investigation of Local Conduction Mechanisms in Ca and Ti-Doped BiFeO3 Using Scanning Probe Microscopy Approach

“…In contrast, the grain boundaries conduction can be apparently distinguished via the cross-section profile lines overlaying the C-AFM and topography scan images (Figure 1g,h). The latter is consistent with the observation of the n-type conductivity in pure BFO, where the conduction is supported by thermally activated electrons from defect (oxygen vacancies) states [25][26][27][28][29][30][31][32][33][34]. It is worth noting that the conductivity of Ca/Ti-doped BFO can change from n-to p-type depending on defect structure and synthesis conditions [37].…”

“…Depending on the defect structure, both p-and n-type conductivity associated with the DW were found [16,29,30]. The p-type conductivity is due to charge transfer between Fe 4+ and Fe 3+ [2,16,[25][26][27][28][29][30][31][32][33][34], while the n-type conductivity is linked to the formation of oxygen vacancies [16,[25][26][27][28][29][30][31][32][33][34]. Some alternative mechanisms of conductivity in polycrystalline BFO suggesting the reduction of local bandgap at the boundaries [13,26] were also considered.…”

Controllable Distribution and Reversible Migration of Charges in BiFeO3-Based Films on Si Substrates

“…As one of the few known ferroelectric and magnetic materials at room temperature, , BFO, possessing large spontaneous polarization, has been widely studied for the ferroelectric storage, − magnetoelectric coupling, ,, and so forth. The small band gap (2.7 eV) , of BFO has also attracted much attention in the field of optoelectronics. − In addition, correlated with the volatilization of Bi, the valence change in Fe, the lack of oxygen, and the charge migration and distribution could greatly influence the electrical, magnetic, and optical properties of BFO low-dimensional materials. − …”