Orbital-Energy Splitting in Anion Ordered Ruddlesden-Popper Halide Perovskites for Tunable Optoelectronic Applications

TL;DR

This study uses first-principles calculations to link atomic orbital characteristics with optoelectronic properties in layered halide perovskites, enabling targeted orbital engineering to enhance photovoltaic performance.

Contribution

It introduces a simple band structure parameter, $ig|ig| ext{Δ}cig|ig|$, to optimize optoelectronic properties in layered halide perovskites through orbital splitting control.

Findings

Reducing orbital splitting $| ext{Δ}c|$ lowers band gap and effective masses.

Orbital splitting control improves optical absorption in visible spectrum.

The approach extends to other non-cubic halide perovskites.

Abstract

The electronic orbital characteristics at the band edges plays an important role in determining the electrical, optical and defect properties of perovskite photovoltaic materials. It is highly desirable to establish the relationship between the underlying atomic orbitals and the optoelectronic properties as a guide to maximize the photovoltaic performance. Here, using first-principles calculations and taking anion ordered Ruddlesden-Popper (RP) phase halide perovskites Cs$_{n+1}$Ge$_n$I$_{n+1}$Cl$_{2n}$ as an example, we demonstrate how to rationally optimize the optoelectronic properties (e.g., band gap, transition dipole matrix elements, carrier effective masses, band width) through a simple band structure parameter. Our results show that reducing the splitting energy $|\Delta c|$ of p orbitals of B-site atom can effectively reduce the band gap and carrier effective masses while greatly improving the optical absorption in the visible region. Thereby, the orbital-property relationship with $\Delta c$ is well established through biaxial compressive strain. Finally, it is shown that this approach can be reasonably extended to several other non-cubic halide perovskites with similar p orbitals characteristics at the conduction band edges. Therefore, we believe that our proposed orbital engineering approach provides atomic-level guidance for understanding and optimizing the device performance of layered perovskite solar cells.