Quantifying the Excitonic Static Disorder in Organic Semiconductors

TL;DR

This paper introduces a novel method to accurately measure excitonic static disorder in organic semiconductors using photovoltaic spectra, revealing its independence from Urbach energy and providing insights into disorder's impact on device performance.

Contribution

It presents a new approach and computational framework for quantifying excitonic static disorder, considering optical interference effects, in various organic semiconductor blends.

Findings

Static disorder is uncorrelated with Urbach energy.

Disorder can be accurately measured from photovoltaic spectra.

Quantified disorder in high-efficiency blends like PM6:Y6.

Abstract

Organic semiconductors are disordered molecular solids and as a result, their internal charge dynamics and ultimately, the performance of the optoelectronic devices they constitute, are governed by energetic disorder. To ascertain how energetic disorder impacts charge generation, exciton transport, charge transport, and the performance of organic semiconductor devices, an accurate approach is first required to measure this critical parameter. In this work, we show that the static disorder has no relation with the so-called Urbach energy in organic semiconductors. Instead, it can be obtained from photovoltaic external quantum efficiency spectra at wavelengths near the absorption onset. We then present a detailed methodology, alongside a computational framework, for quantifying the static energetic disorder associated with singlet excitons. Moreover, the role of optical interference in this analysis is considered to achieve a high-accuracy quantification. Finally, the excitonic static disorder was quantified in several technologically-relevant donor-acceptor blends, including high-efficiency PM6:Y6.