Ellipsoid-based Coarse-grained Molecular Dynamics Simulation of Morphology Evolution of Small Molecule Organic Solar Cells during Vacuum Deposition Process

Ping-Han Tang^1*, Chun-Wei Pao¹

¹Research center for applied sciences, academia sinica, taipei, Taiwan

* Presenter:Ping-Han Tang, email:pinhamtang@gmail.com

Vacuum deposition of organic small molecules has been applied to the fabrication of many flexible optoelectronic device such as small molecule solar cells and organic light emitting diodes. The morphology of the molecular film during and after deposition processes is one of the crucial issues to affect the performance of these device. In this study, we investigated the morphology evolution of DPDCPB: C₇₀ small molecule solar cells during vacuum co-deposition processes by carrying out a series of GPU-accelerated, multiscale, coarse-grained molecular dynamics (CGMD) simulations. By coarsing DPDCPB and C₇₀ molecules into ellipsoid beads, we were able to simulate morphology evolution of system with system length scale compatible with experiments (c.a. 50 nm). The Gay-Berne force field was parametrized using genetic algorithm to reproduce potential energy surfaces from respective all-atom molecular simulations. We systematically investigated morphology evolution of the active layer with different donor:acceptor ratio as well as deposition rates. The present study demonstrates that ellipsoid-based coarse-grained model allows us to study morphology evolution of small molecule organic thin film during vacuum deposition processes with unprecedented details, and provides valuable insights into the correlations between blending ratio, deposition rates, and resultant film morphologies, thereby helping experimental teams optimize device fabrication protocols for the next generation organic optoelectronic devices.

Keywords: Organic solar cell, Vacuum deposition, Coarse-grained molecular dynamics, Gay-Berne force field