Spin-conserving Boltzmann theory for carriers and excitons in organic semiconductors

TL;DR

This paper introduces a semiclassical Boltzmann theory for organic semiconductors that models both charge transport and excitonic processes, including spin conservation and many-particle effects, aiding in organic solar cell research.

Contribution

It develops a comprehensive Boltzmann framework that accounts for spin-conserving excitonic and charge dynamics with matrix-valued distributions, advancing modeling capabilities in organic electronics.

Findings

Quadrupolar terms are essential for triplet exciton modeling.

The theory incorporates fermionic and bosonic many-particle effects.

Provides a basis for improved organic solar cell simulations.

Abstract

The rise of organic electronics calls for versatile modeling tools. In this context, we develop a semiclassical Boltzmann theory that describes transport and excitonic processes in crystalline organic semiconductors on equal footing. The generation of singlet and triplet excitons out of the ground state, their formation from free electrons and holes, the reverse processes, as well as the fusion and fission of excitons are included. The corresponding scattering integrals respect spin conservation, which requires matrix-valued distribution functions. They also include fermionic and bosonic many-particle effects such as Pauli blocking. We employ a multipole expansion of the distribution functions, where quadrupolar terms turn out to be essential for the triplet excitons. This work provides a basis for the modeling of organic solar cells, in which excitonic processes are crucial for the performance. Moreover, the theory is of general interest for transport and transitions of multiple (quasi-) particle species carrying spin in nonequilibrium systems.