Theoretical Prediction of Electron Mobility in Birhodanine Crystals and their Sulfur Analogues

TL;DR

This study compares semi-classical and Marcus-Levich-Jortner models to predict electron mobility in birhodanine crystals, finding MLJ aligns better with experiments and highlighting model sensitivities to reorganization energy.

Contribution

It provides a detailed comparison of SCM and MLJ models for charge mobility prediction in organic crystals, guiding model selection based on accuracy and sensitivity.

Findings

MLJ approach predicts electron mobility consistent with experiments.

MLJ's predictions are highly sensitive to external reorganization energy.

SCM underestimates electron mobility compared to MLJ.

Abstract

Molecular crystals compose the current state of the art when it comes to organic-based optoelectronic applications. Charge transport is a crucial aspect of their performance. The ability to predict accurate electron mobility is needed in designing novel organic semiconducting materials. In the present work, the Semi-Classical Marcus (SCM) and Marcus-Levich-Jortner (MLJ) hopping models are employed to numerically describe the charge mobility in six distinct birhodanine-like crystals. These materials were recently used in n-channel organic transistors as electron transporting layers. Results have revealed that the MLJ approach predicts electron mobilities in good agreement with the experiment, whereas SCM underestimates this parameter. Remarkably, we found for one of the birhodanine derivatives studied here average electron mobility of 0.14 cm^2 V^(-1) s^(-1), which agrees with the one reported in experimental investigations. Moreover, it was identified that the MLJ approach presents a strong dependency on external reorganization energy. For SCM, a change in the reorganization energy value has a small impact on mobility, while for MLJ it impacts the average electron mobility that exponentially decays by increasing the external reorganization energy. Importantly, we highlight the primary source of the differences in predicting the electron mobility presented by both approaches, providing useful details that will help the selection of one of these two models for study different species of organic molecular crystals.