Electroluminescence spectra in weakly coupled single-molecule junctions

TL;DR

This paper presents a combined ab initio and rate-equation approach to analyze electroluminescence spectra in single-molecule junctions, accurately capturing vibrational effects and explaining experimental features.

Contribution

The authors develop a comprehensive method that incorporates the full vibrational spectrum to quantitatively match experimental electroluminescence spectra in single-molecule junctions.

Findings

Good agreement with experimental spectral features and voltage dependence.

Quantum yield decreases at high bias, matching observations.

Vibrational relaxation times influence spectral features.

Abstract

We have combined ab initio quantum chemistry calculations with a rate-equation formalism to analyze electroluminescence spectra in single-molecule junctions, measured recently by several groups in Scanning Tunneling Microscope setups. In our method, the entire vibrational spectrum is taken into account. Our method leads to good quantitative agreement with both the spectroscopic features of the measurements and their current and voltage dependence. Moreover, our method is able to explain several previously unexplained features. We show that in general, the quantum yield is expected to be suppressed at high bias, as is observed in one of the measurements. Additionally, we comment on the influence of the vibrational relaxation times on several features of the spectrum.