Interfacial effect on the optoelectronic and piezoelectric properties of Ge-Sn terminated Halide Perovskite heterostructure from first-principles study

TL;DR

The study addresses the need for eco-friendly energy materials by evaluating Pb-free halide perovskites CsGeCl3 and RbSnBr3 via first-principles DFT for bulk, surfaces, and Ge–Sn terminated interfaces. Using GGA and mGGA functionals, the authors analyze electronic, optical, and piezoelectric responses across bulk, surface, and heterostructure configurations. Key findings include a direct band gap for CsGeCl3 and an indirect gap for RbSnBr3, Type II band alignment at the CsGeCl3/RbSnBr3 interface, and large piezoelectric coefficients up to approximately $e_{ij} \approx 2.3$ C/m$^2$ with electromechanical couplings $k_{ij}$ up to around $2.9$ in the mGGA case. These interfacial polarization effects and robust optoelectronic and piezoelectric responses suggest strong potential for photovoltaic, optoelectronic, and piezoelectric energy harvesting with Pb-free materials.

Abstract

Since the very early stages of research on sustainable technologies, green energy conversion has always been a prime focus. With the discoveries of countless functional materials in recent years, significant progress has been made to meet the global energy demand for sustainable development. Among them, halide perovskites have emerged as one of the most promising and reliable materials. In this work, we have investigated the lead-free halide perovskites, vis CsGeCl3 and RbSnBr3, within a framework of density functional theory (DFT) to explore their potential applicability in harvesting clean and renewable energy. This study gives a comprehensive analysis of the bulk, surface (001), and Ge-Sn-terminated interfaces within GGA and mGGA functionals. Interestingly, the inherent asymmetric arrangements of the systems exhibit remarkable optoelectronic and piezoelectric properties. The piezoelectric performance of each surface cut has been validated through the electromechanical coupling calculation.

Figures (9)

• Figure 1: Schematic 3D figures of the bulk perovskites
• Figure 2: Molecular dynamic simulations of bulk CsGeCl$_3$- Fig.(a&b) and RbSnBr$_3$- Fig.(c&d) using GGA and mGGA
• Figure 3: Band structures and DOS of CsGeCl$_3$ Fig.(a & b) and RbSnBr$_3$ Fig.(c & d).
• Figure 4: Schematic surface structures of CsGeCl$_3$ (001) and RbSnBr$_3$ (001)
• Figure 5: Relaxation energies (E$_r$), Cleavage energies (E$_c$), and Surface energies (E$_{surface}$) of CsGeCl$_3$ (001) and RbSnBr$_3$ (001)