Tuning the optical bandgap in hybrid layered perovskites through variation of alkyl chain length

TL;DR

This study explores how changing the alkyl chain length in layered hybrid perovskites affects their optical bandgap, revealing a significant blueshift linked to structural tilting and providing insights into tuning material properties.

Contribution

It demonstrates the impact of organic ligand chain length on the optical properties and structure of 2D perovskites, highlighting the role of octahedral tilting in bandgap tuning.

Findings

Blueshift in optical spectra with increasing chain length

A 110 meV jump in transition energy between n=10 and n=12

Effective mass model agrees with experimental data

Abstract

Recently, layered hybrid perovskites have been attracting huge interest due to a wide range of possible chemical compositions and the resulting tunability of the materials properties. In this study, we investigate the effect of the chain length of the organic ligands on the optical properties of stacks of two dimensional perovskite layers consisting of alkylammonium lead iodide (CnH2n+1NH3)2PbI4 with n=4-18. Photoluminescence and absorption spectroscopy reveal a blueshift with increasing chain length n including a jump of 110 meV between the n=10 and n=12 ligands due to a change in octahedral tilting. Using Xray diffraction (XRD) we determine the crystal structure and find the octahedral tilting to be the main cause of this blueshift. However, for very short chain lengths additional effects further reduce the transition energy. Results of effective mass approximation model calculations show good agreement between the expected reduction of transition energy and measured photoluminescence emission wavelength for these samples. This highlights how octahedral tilting plays a major role in determining the optical bandgap and suggests that miniband formation plays only a minor role in this material.