Absolute energy level positions in tin- and lead-based halide perovskites

Shuxia Tao,Ines Schmidt,Ionut Tranca,Klaus Meerholz,Geert Brocks,Selina Olthof,Junke Jiang

doi:10.1038/s41467-019-10468-7

Abstract

Metal halide perovskites are promising materials for future optoelectronic applications. One intriguing property, important for many applications, is the tunability of the band gap via compositional engineering. While experimental reports on changes in absorption or photoluminescence show rather good agreement for different compounds, the physical origins of these changes, namely the variations in valence and conduction band positions, are not well characterized. Here, we determine ionization energy and electron affinity values of all primary tin- and lead-based perovskites using photoelectron spectroscopy data, supported by first-principles calculations and a tight-binding analysis. We demonstrate energy level variations are primarily determined by the relative positions of the atomic energy levels of metal cations and halide anions and secondarily influenced by the cation-anion interaction strength. These results mark a significant step towards understanding the electronic structure of this material class and provides the basis for rational design rules regarding the energetics in perovskite optoelectronics.

Highlights

Metal halide perovskites are promising materials for future optoelectronic applications
This way, the positions of E = 0 eV corresponds to the vacuum level and the onset positions of the valence band and conduction band directly match the Ionization Energy (IE) and Electron Affinity (EA) values. These valence band maximum (VBM) and conduction band minimum (CBM) positions are indicated by black vertical markers and are extracted by correlating the measured spectra with density of states (DOS) obtained from first-principles calculations as elaborated below
We suggest that the inconsistency between the density- functional-theory (DFT) and IPES-derived DOSs may have to do with significant differences in measurement cross section

Summary

Introduction

Metal halide perovskites are promising materials for future optoelectronic applications. It should be noted that we have extensively optimized the preparation procedure of each compound and have further evaluated the quality of our samples with respect to elemental composition, oxidation state, crystal structure, and morphology; the corresponding measurements can be found in the Supplementary Notes 1–18.

Results

Conclusion