Phase field simulations of thermal annealing for all-small molecule organic solar cells

TL;DR

This paper uses phase field simulations to analyze how thermal annealing influences the nanomorphology of all-small molecule organic solar cells, revealing key physical mechanisms behind morphological evolution.

Contribution

It introduces a phase field simulation approach to study the effects of thermal annealing on BHJ morphology in all-small molecule OSCs, linking physical phenomena to morphological changes.

Findings

Morphological evolution is dominated by dissolution of small crystals.

Large crystals grow anisotropically during annealing.

Simulation results align with experimental observations.

Abstract

Interest in organic solar cells (OSCs) is constantly rising in the field of photovoltaic devices. The device performance relies on the bulk heterojunction (BHJ) nanomorphology, which develops during the drying process and additional post-treatment. This work studies the effect of thermal annealing (TA) on an all-small molecule DRCN5T: PC71 BM blend with phase field simulations. The objective is to determine the physical phenomena driving the evolution of the BHJ morphology for a better understanding of the posttreatment/morphology relationship. Phase-field simulation results are used to investigate the impact on the final BHJ morphology of the DRCN5T crystallization-related mechanisms, including nucleation, growth, crystal stability, impingement, grain coarsening, and Ostwald ripening, of the amorphous-amorphous phase separation (AAPS), and of diffusion limitations. The comparison of simulation results with experimental data shows that the morphological evolution of the BHJ under TA is dominated by dissolution of the smallest, unstable DRCN5T crystals and anisotropic growth of the largest crystals.