Mo substitution in ferroelectric perovskite oxides towards transparent photovoltaic applications

Photovoltaic (PV) devices are a promising clean energy solution. However, they are limited by their efficiency, due to which even within the value of its theoretical limit, large areas will have to be covered with them in order to meet the energy requirements of society. To overcome the coverage issue, transparent PV (TPV) can be used, since their transparency allows coverage of larger surfaces. TPV has low efficiency since they do not absorb visible light. To improve the efficiency, ferroelectric perovskite oxides can be used since ferroelectric oxides perovskites-based PV devices can, in principle, exhibit higher efficiency due to the bulk photovoltaic effect (BPVE).

In this study, novel ferroelectric perovskite oxides systems had their band-gap engineered by Mo substitution, to fit to the PV/TPV requirements (

Substitution of Mo and Mg at the B-site in parent BaTiO₃ was done[1], leading to a band-gap decrease to the TPV target value of 2.8 eV while maintaining ferroelectric polarization. This material was experimentally realized by the group of Prof. Jonathan Spanier at Drexel University (Philadelphia, PA). In addition, a second BaTiO₃ derivative was studied, which is substituted with Na at the A-site and Mo or W at the B-site of the perovskite. The system shows an improvement relative to the prior system in its ability to maintain ferroelectric polarization, while having similar band-gap in the TPV region.

A novel potassium-based perovskites system of [KTi_0.5Mo_0.5O₃] was studied and was found to have a lower gap than the one necessary for TPV (2.7 eV). Therefore, a solid solution of [KTi_0.5Mo_0.5O₃] system with KNbO₃ to form [KNbO₃]_0.5–[KTi_0.5Mo_0.5O₃]_0.5 was studied. The result solid solution exhibits a band-gap in the TPV target in its most stable studied phase. This system is currently being studied experimentally by Prof. Yang Bai at University of Oulu (Oulu, Finland).

[1] O. Shafir, J. Yang, A. M. Rappe, and I. Grinberg, “Ferroelectric barium titanate derivatives containing Mo and Mg for transparent photovoltaic applications,” J. Appl. Phys., vol. 126, no. 17, p. 174101, Nov. 2019.

[2] O.Shafir, A. Shopin, and I. Grinberg "Band-gap engineering of W- and Mo-containing perovskite oxides derived from barium titanate" Phys. Rev. Applied (under review)