Nature of the singlet and triplet excitations mediating thermally activated delayed fluorescence

Olivier, Yoann; Yurash, Brett; Muccioli, Luca; D’Avino, Gabriele; Mikhnenko, Oleksandr V.; Sancho-García, Juan-Carlos; Adachi, Chihaya; Nguyen, Thuc‐Quyen; Beljonne, David

doi:10.1103/physrevmaterials.1.075602

Cited by 122 publications

(193 citation statements)

References 37 publications

Supporting

Mentioning

176

Contrasting

Order By: Relevance

“…S tudies of UV-Vis-NIR absorption for conventional semiconductors usually focus on the absorption strength and the energy of spectral features. This is similar for organic semiconductors, which exhibit strong excitonic effects 1 and for which the nature of the excitons (molecular excitons, chargetransfer (CT) excitons or hybrids) and their connection to performance limitations of optoelectronic devices are of great interest [2][3][4][5][6][7] . For instance, the physical mechanisms and microscopic interactions that influence the key electron-transfer events in OSCs are broadly debated 1,3,[8][9][10][11][12] and can be studied by absorption spectroscopy.…”

mentioning

confidence: 87%

Molecular vibrations reduce the maximum achievable photovoltage in organic solar cells

et al. 2020

View full text Add to dashboard Cite

The low-energy edge of optical absorption spectra is critical for the performance of solar cells, but is not well understood in the case of organic solar cells (OSCs). We study the microscopic origin of exciton bands in molecular blends and investigate their role in OSCs. We simulate the temperature dependence of the excitonic density of states and low-energy absorption features, including low-frequency molecular vibrations and multi-exciton hybridisation. For model donor-acceptor blends featuring charge-transfer excitons, our simulations agree very well with temperature-dependent experimental absorption spectra. We unveil that the quantum effect of zero-point vibrations, mediated by electron-phonon interaction, causes a substantial exciton bandwidth and reduces the open-circuit voltage, which is predicted from electronic and vibronic molecular parameters. This effect is surprisingly strong at room temperature and can substantially limit the OSC's efficiency. Strategies to reduce these vibration-induced voltage losses are discussed for a larger set of systems and different heterojunction geometries.

show abstract

mentioning

confidence: 87%

Molecular vibrations reduce the maximum achievable photovoltage in organic solar cells

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Fortunately, the computational design of novel conjugated organic materials has significantly contributed to the field, first applying a variety of modelling techniques for the fast screening of the compounds, and then rationalizing the physical origin of small ∆E ST together with other competitive factors such as the impact of the spin-orbit coupling (SOC or V SOC ). Despite significant advances in the study and influence of SOC [11][12][13], which also contributes to the RISC rate as k RISC ∝ V 2 SOC , in the following we concentrate on the former ∆E ST quantity for simplicity.…”

Section: Current Achievements and Challenges For Theoretical Methods mentioning

confidence: 99%

Computational Studies of Molecular Materials for Unconventional Energy Conversion: The Challenge of Light Emission by Thermally Activated Delayed Fluorescence

2020

View full text Add to dashboard Cite

In this paper we describe the mechanism of light emission through thermally activated delayed fluorescence (TADF)—a process able to ideally achieve 100% quantum efficiencies upon fully harvesting the energy of triplet excitons, and thus minimizing the energy loss of common (i.e., fluorescence and phosphorescence) luminescence processes. If successful, this technology could be exploited for the manufacture of more efficient organic light-emitting diodes (OLEDs) made of only light elements for multiple daily applications, thus contributing to the rise of a sustainable electronic industry and energy savings worldwide. Computational and theoretical studies have fostered the design of these all-organic molecular emitters by disclosing helpful structure–property relationships and/or analyzing the physical origin of this mechanism. However, as the field advances further, some limitations have also appeared, particularly affecting TD-DFT calculations, which have prompted the use of a variety of methods at the molecular scale in recent years. Herein we try to provide a guide for beginners, after summarizing the current state-of-the-art of the most employed theoretical methods focusing on the singlet–triplet energy difference, with the additional aim of motivating complementary studies revealing the stronger and weaker aspects of computational modelling for this cutting-edge technology.

show abstract

“…The most common design strategy of TADF emitters consists in partitioning hole and electron densities over different spatial regions via electron donating (D) and accepting (A) units, often connected in a twisted conformation, hence reducing exchange interactions splitting singlets from triplets [6][7][8][9] . In actual cases, the excited states involved in TADF often turn out to be hybrid mixtures of charge transfer (CT) and local excitation (LE) diabatic states, with the amount of mixing prompted by vibronic coupling 10,11 . We refer the interested reader to a recently published review 12 for a critical discussion of the chemical design rules that have emerged so far through the fruitful interplay between theoretical and experimental chemists.…”

mentioning

confidence: 99%

Computational Design of Thermally Activated Delayed Fluorescence Materials: The Challenges Ahead

Olivier

Sancho‐García

Muccioli

et al. 2018

J. Phys. Chem. Lett.

Self Cite

137

188

View full text Add to dashboard Cite

Thermally activated delayed fluorescence (TADF) offers the premise for all-organic light emitting diodes with quantum efficiencies competing those of transition metal-based phosphorescent devices. While computational efforts have so far largely focused on gas-phase calculations of singlet and triplet excitation energies, the design of TADF materials requires multiple methodological developments targeting among others a quantitative description of electronic excitation energetics, fully accounting for environmental electrostatics and molecular conformational effects, the accurate assessment of the quantum-mechanical interactions that trigger the elementary electronic processes involved in TADF, as well as a robust picture for the dynamics of these fundamental processes. In this perspective, we describe some recent progress along those lines and highlight the main challenges ahead for modeling, which we hope will be useful to the whole TADF community.

show abstract

Nature of the singlet and triplet excitations mediating thermally activated delayed fluorescence

Cited by 122 publications

References 37 publications

Molecular vibrations reduce the maximum achievable photovoltage in organic solar cells

Molecular vibrations reduce the maximum achievable photovoltage in organic solar cells

Computational Studies of Molecular Materials for Unconventional Energy Conversion: The Challenge of Light Emission by Thermally Activated Delayed Fluorescence

Computational Design of Thermally Activated Delayed Fluorescence Materials: The Challenges Ahead

Contact Info

Product

Resources

About