Global Theory of Equilibrium and Nonequilibrium Exciton Dynamics in Disordered Semiconductors
Stavros Athanasopoulos a, Mehdi Ansari-Rad b
a Departamento de Física, Universidad Carlos III de Madrid, Avenida Universidad 30, Leganés 28911, Madrid, Spain
b Department of Physics, Shahrood University of Technology, Shahrood 3619995161, Iran
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference on Perovskite and Organic Photovoltaics and Optoelectronics (IPEROP19)
Kyōto-shi, Japan, 2019 January 27th - 29th
Organizers: Hideo Ohkita, Atsushi Wakamiya and Mohammad Nazeeruddin
Oral, Stavros Athanasopoulos, presentation 073
DOI: https://doi.org/10.29363/nanoge.iperop.2019.073
Publication date: 23rd October 2018

The phenomenon of exciton diffusion is found to play a role in a remarkably wide range of physical systems, including disordered organic semiconductors [1], nanocrystalline quantum dots [2], semiconducting carbon nanotubes and photosynthetic biological systems. Moreover, there is a growing interest in describing electronic excitation energy transfer because exciton dynamics determines function in many technological applications. For example, in thin film organic solar cells, exciton diffusion drives charge separation, in organic light emitting diodes it determines the brightness and color of the device, in scintillator detectors it controls the response function and yield, while in quantum communication systems it facilitates photon antibunching. Whilst significant progress has been made on understanding temperature dependent spectral relaxation and exciton diffusion, including experimental measurements and computational models [1-5], currently there is no analytical theory that can describe the transition from equilibrium to non-equilibrium transport.

In this talk, I will present a temperature dependent theory for singlet exciton hopping transport in disordered semiconductors [6]. It draws on the transport level concept within a Förster transfer model and bridges the gap in describing the transition from equilibrium to non-equilibrium time dependent spectral diffusion. We test the validity range of the developed model using kinetic Monte Carlo simulations and find agreement over a broad range of temperatures. It reproduces the scaling of the diffusion length [3] and spectral shift [5] with the dimensionless disorder parameter and describes in a unified manner the transition from equilibrium to non-equilibrium transport regime. We find that for Förster radius values smaller than 5 nm, typical in organic semiconductors, exciton transport occurs mainly in the nonequilibrium regime and the diffusion length deviates from the cubic dependence upon the Förster radius. The developed theory provides a powerful tool for interpreting time-resolved and steady state spectroscopy experiments in a variety of disordered materials, including organic semiconductors and colloidal quantum dots.

This project has received funding from the Universidad Carlos III de Madrid, the European Union’s Seventh Framework Programme for research, technological development, and demonstration under Grant Agreement No. 600371, el Ministerio de Economía, Industria y Competitividad (COFUND2014- 51509), el Ministerio de Educación, cultura y Deporte (CEI- 15-17), and Banco Santander.

© Fundació Scito
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