Tunability of electronic and optical properties of the Ba–Zr–S system via dimensional reduction

Abstract

Transition metal sulfide perovskites offer lower band gaps and greater tunability than oxides, along with other desirable properties for applications. Here we explore dimensional reduction as a tuning strategy using the Ruddlesden-Popper phases in the Ba-Zr-S system as a model. The three dimensional perovskite BaZrS3 is a direct gap semiconductor, with a band gap of 1.5 eV suitable for solar photovoltaic application. However, the three known members of the Ruddlesden-Popper series, are all indirect gap materials, and additionally have lower fundamental band gaps. This is accompanied in the case of Ba2ZrS4 by a band structure that is more favorable for carrier transport for oriented samples. The layered Ruddlesden-Popper compounds show significantly anisotropic optical properties, as may be expected. The optical spectra show tails at low energy, which may complicate experimental characterization of these materials.

Band gap evolution in Ruddlesden-Popper phases

“…Alloying is a common approach to tune the band gap of such semiconductors, yet the accompanying disorder has the undesirable effect of lowering carrier mobility [15,16]. RP phases offer an alternative approach to create long range ordered structures to tune the physical properties such as band gap [13,14,[17][18][19][20][21][22]. While the changes in the band gap through alloying can be understood in terms of orbital composition (by chemical substitutions) of the valence and/or conduction-band edge states, it is yet unclear how the quantum confinement through reduced dimensionality, and details of the crystal structure of the RP phases modify the band gap with respect to the ABX 3 parent material.…”

Chalcogenide Perovskites and Perovskite-Based Chalcohalide as Photoabsorbers: A Study of Their Properties, and Potential Photovoltaic Applications

“…There are various ways by which dimensional reduction can be accomplished in the electronic material scheme through artificial methods, for instance, superlattices, exfoliation, or thin-film development to yield 2D perovskite compounds, bonding structures that reduce the active dimensionality, interfacial electron gasses, and production of the Ruddlesden-Popper (R.P.) sequences for perovskites [37]. 2D perovskite compounds have made available novel properties, approaching innovative design conventions for system application and forming new structures [38].…”

“…2D perovskite compounds have made available novel properties, approaching innovative design conventions for system application and forming new structures [38]. Moreover, dimensional reduction produces changes associated with the electronic form of the materials, resulting in their broad range of uses and comprising, for instance, thermoelectric, where thermal power and conductivity can be decoupled, and optoelectronic components such as plain conductors, as well as a broad selection of other optical and electronic functions based on 2D compounds [37].…”

Special issue in honor of Eberhard K.U. Gross for his 65th birthday

“…The optical properties of quantum dots of Cu 2 ZnSn(Se,S) 4 , a material currently investigated for its use as an absorber in photovoltaic cells, is investigated in [50]. In [51], the authors propose a way to tune the electronic and optical properties of the Ba-Zr-S system via dimensional reduction. Finally, Nazarov looks at the collective and independent-particle excitations in quasi-2D electron gas with one filled miniband [52].…”