Ultrafast nonadiabatic relaxation of photoexcited phenyl-C₆₁ butyric acid methyl ester molecule

Highly efficient polymer-fullerene based OPV devices employ polymer functionalized fullerenes P-C_n, such as phenyl-C₆₁ butyric acid methyl ester (PCBM), as electron acceptors [1]. In general, the success of functional fullerenes as acceptors, electron selective layers, and morphology stabilizers of bulk heterojunction polymer solar cells is now established [2]. This high degree of versatility in P-C_n functionality in OPV makes a fundamental understanding of its hot carrier relaxation dynamics an essential test case to probe the process. In this work, we use an approach of electron-phonon coupled nonadiabatic molecular dynamics (NAMD) [3] to simulate the relaxation of a photoexcited PCBM molecule. The methodology relies on a combination of the fewest-switches surface hopping approach and Kohn−Sham single-particle description in density functional theory (DFT) using Libra software [4]. Comparisons with the results from pristine C₆₀ will be made at various stages to capture the effects of polymer functionalization on the dynamics.

[1] G.J. Hedley et al, Nat. Commun. 4, 2867 (2013).

[2] C.-Z. Li et al, J. Mater. Chem. 22, 4161, (2012).

[3] M.E. Madjet et al, Phys. Rev. Lett. 126, 183002, (2021).

[4] M. Shakiba et al, Software Impacts 14 100445 (2022).