# Strain-engineered Si-doped Cs3Bi2I9 perovskite for high-performance MIM capacitors: a DFT study

## TL;DR

This paper explores how silicon doping and strain engineering can improve the energy storage properties of a lead-free perovskite material for use in high-performance capacitors.

## Contribution

The study demonstrates that Si-doping combined with strain-engineering can enhance dielectric properties in Cs3Bi2I9 perovskite.

## Key findings

- Undoped Cs3Bi2I9 has a wide band gap and low polarization, making it a stable insulator.
- 0.25 mol% Si doping narrows the band gap and increases dielectric constant and capacitance.
- Strain engineering enhances polarization and piezoelectricity in Si-doped systems.

## Abstract

This study examines the energy storage potential of strain engineered Si doped Cs3Bi2I9 perovskites using density functional theory. Key electronic and electromechanical parameters—band gap, born effective charge, polarization, piezoelectricity, and leakage suppression—were evaluated for intrinsic and strained systems. Undoped Cs3Bi2I9 exhibits a wide 3.3 eV band gap and low polarization, making it suitable as a stable insulating material. Introducing 0.25 mol% Si narrows the band gap and introduces beneficial defects that enhance the dielectric constant and capacitance, with BEC analysis revealing strong local polarization around Si atoms and increased anisotropic stiffness. Under 0.10% strain, the 0.25 mol% Si doped system achieves polarization nearing 1C m−2, strong out of plane piezoelectricity, and reduced leakage—properties ideal for flexible electronics and energy storage devices. In contrast, 0.50 mol% Si under strain shows excessive polarization and higher leakage due to larger lattice distortion. This work provides the first demonstration that Si-doping synergistically combined with strain-engineering can unlock high-κ dielectric behavior and enhanced polarization in Cs3Bi2I9, establishing a new, lead-free perovskite platform for next-generation MIM capacitors.

This study examines the energy storage potential of strain engineered Si doped Cs3Bi2I9 perovskites using density functional theory.