Influence of Nonuniform Exciton Density on Diffusion Length Measurements via Photoluminescence Quenching - Article

Sep 29, 2026

Investigating exciton transport is central to improving energy-efficiency in organic photovoltaics (OPVs), where diffusion length (LD) summarizes overall transport efficiency. Photoluminescence quenching is widely used to measure LD, but bilayer quencher geometries can introduce bias because exciton generation is often assumed incorrectly. This study quantifies LD errors arising from wrong exciton generation assumptions and finds the error strongly depends on molecular absorption. Analysis of common organic compounds indicates errors up to 30%, highlighting a key limitation in common protocols.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Abstract

1. Introduction

Exciton diffusion and diffusion length in OPVs

LD estimation using photoluminescence quenching

Limits of analytic solutions under homogeneous generation assumptions

This article is licensed under CC-BY 4.0 [http://pubs.acs.org/journal/acsodf](http://pubs.acs.org/journal/acsodf) Article Influence of Nonuniform Exciton Density on Diffusion Length Measurements via Photoluminescence Quenching Published as part of ACS Omega special issue “Chemistry in Brazil: Advancing through Open Science”. Bruno Guilherme Araujo Pimenta, Tiago de Sousa Aráujo Cassiano, Ricardo Gargano, and Pedro Henrique de Oliveira Neto* Cite This: ACS Omega 2025, 10, 58383−58392 Read Online | | | | | | | | --- | --- | --- | --- | --- | --- | | ACCESS | Metrics & More | | Article Recommendations | | *sı Supporting Information | ABSTRACT: Addressing the challenge of energy efficiency inorganic photovoltaics (OPVs) requires investigating exciton transport mechanisms. Exciton migration in OPVs is influenced by factors such as the morphology, temperature, absorption properties, and excitation conditions. In this context, the diffusion length (LD) is a key parameter that characterizes overall transport efficiency. Spectroscopic techniques, particularly photoluminescence quenching, are commonly used for LD measurements. However, in bilayer quencher setups, these measurements can be limited by assumptions about exciton behavior, potentially leading to inaccurate LD estimates. In this work, we assess the magnitude of error in LD measurements resulting from incorrect exciton generation assumptions. It was found that the error largely depends on the molecules’ absorption characteristics. An analysis of common organic compounds suggests errors of up to 30%. The findings reveal an important limitation in commonly adopted experimental protocols that estimate the diffusion length. Moreover, assessing the error magnitude might aid in the interpretation of future experimental characterizations, furthering the understanding of exciton dynamics in practical setups. 1. INTRODUCTION Organic photovoltaics (OPVs) setups are one of the most promising candidates for renewable energy sources, owing to their significant low cost, lightweight, and flexibility. 1−3 Significant progress toward industrial use has been made through important advances in stability4,5 and efficiency.6 Today, operational OPVs with efficiencies nearing 20% are a reality,6−8 offering an encouraging prospect for future optoelectronics. The OPV operation involves the diffusion of bound electron−hole pairs, known as excitons.9 Therefore, from an efficiency perspective, the focus revolves around understanding exciton migration.10, 11 Toward this task, accurate experimental and theoretical characterizations are essential. Specifically, the diffusion length (LD) is commonly used as a metric to measure a key aspect of the OPV’s potential, playing a central role invalidating and directing new OPV architectures. Fundamentally, exciton diffusion consists of dynamical competition among transfer, recombination, and emission processes. The f̈orster resonance energy transfer (FRET) is the leading theory that models intermolecular exciton hopping,12 relating the transfer rate to the molecule’s optoelectronic properties. One way to connect this description with the diffusion mechanism is by numerically simulating the transport through the kinetic Monte Carlo (KMC) algorithm.13, 14 In this formalism, hopping and decay events are represented as rates given by FRET theory.15, 16 Through this protocol, morphological effects11, 17 as well as complex recombination processes such as singlet−triplet conversions, 18 thermally activated delayed fluorescence, 19,20 and annihilation 14,21−25 can betaken into account dynamically. Importantly, the approach allows for direct calculation of the diffusion length.21,26 Experimentally, LD can be estimated through the attenuation of photoluminescence (PL) when mixing the material with quenchers.12,27−29 In bilayer quenchers, the film thickness modulates the attenuation. Effectively, this shifts the quencher interface

FAQs

Why is diffusion length (LD) important in organic photovoltaics?

LD characterizes exciton transport efficiency, which directly influences OPV performance. Accurate LD values guide and constrain new OPV architectures.

How does photoluminescence quenching measure LD?

LD is estimated from the attenuation of photoluminescence when a material is mixed with quenchers. In bilayer setups, film thickness changes the effective quencher interface position and modifies the diffusion path.

What causes inaccurate LD estimates in bilayer quencher measurements?

Common protocols assume correct exciton generation behavior, but bilayer geometries can violate those assumptions. Incorrect exciton generation assumptions lead to LD errors that depend on molecular absorption characteristics, reaching up to about 30% for common organic compounds.

Sep 29, 2026

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