A lattice model approach to the morphology formation from ternary mixtures during the evaporation of one component

Emilio N M Cirillo,Adrian Muntean,Jan Van Stam,Stela-Andrea Muntean,Ellen Moons,Matteo Colangeli

doi:10.1140/epjst/e2019-800140-1

Emilio N M Cirillo, Adrian Muntean + Show 4 more

Open Access

https://doi.org/10.1140/epjst/e2019-800140-1

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Abstract

Stimulated by experimental evidence in the field of solution-born thin films, we study the morphology formation in a three state lattice system subjected to the evaporation of one component. The practical problem that we address is the understanding of the parameters that govern morphology formation from a ternary mixture upon evaporation, as is the case in the fabrication of thin films from solution for organic photovoltaics. We use, as a tool, a generalized version of the Potts and Blume-Capel models in 2D, with the Monte Carlo Kawasaki-Metropolis algorithm, to simulate the phase behaviour of a ternary mixture upon evaporation of one of its components. The components with spin 1, −1 and 0 in the Blume-Capel dynamics correspond to the electron-acceptor, electron-donor and solvent molecules, respectively, in a ternary mixture used in the preparation of the active layer films in an organic solar cell. Furthermore, we introduce parameters that account for the relative composition of the mixture, temperature, and interaction between the species in the system. We identify the parameter regions that are prone to facilitate the phase separation. Furthermore, we study qualitatively the types of formed configurations. We show that even a relatively simple model, as the present one, can generate key morphological features, similar to those observed in experiments, which proves the method valuable for the study of complex systems.

Highlights

Multi-state spin systems on a lattice have been widely studied in the Statistical Mechanics literature, we refer the reader for instance to [33] where efforts have been invested in connecting microscopic dynamics to dynamics at mesoscopic and/or continuum scales
This work is a first step of a program that aims at describing the morphology observed in thin film evaporation experiments on the basis of lattice gas models that are amenable to an analytical or, typically, a numerical investigation
We showed that even this relatively simple model can be used to understand the influence of the multiple external and internal parameters on the morphology formation in ternary systems upon evaporation of one component

Summary

Introduction

Multi-state spin systems on a lattice have been widely studied in the Statistical Mechanics literature, we refer the reader for instance to [33] where efforts have been invested in connecting microscopic dynamics to dynamics at mesoscopic and/or continuum scales. The number Jαγ will be the energy cost of two neighboring spins equal to α and γ With this model at hand, we study the phase separation in a ternary mixture upon evaporation of one of the components. This is a crucial issue in the morphology formation in solution borne thin films, as for example in the preparation of the active layer in organic photovoltaics. The components of the ternary mixture are usually an electron-donor molecule, an electron-acceptor molecule, and a solvent This subject is of large interest in the community and is discussed in many experimental and computational [1,2,18,21,25,26,28,30] studies; see [20] for related work done for stochastic models for competitive growth of phases.

The model

Simulation results and discussion

Conclusions