External electric field control of charge transport in Y-shaped and linear non-fullerene acceptors

Abstract

Achieving a balance between controlled modulation and minimizing sensitivity to external electric fields (EEFs) is essential for improving charge mobility and stability in organic photovoltaics. However, the molecular-level effects of EEF-induced structural and electronic changes on charge transport in non-fullerene acceptors (NFAs) remain unclear. Herein, we reveal EEF-dependent charge transport behavior of representative NFAs, including Y-shaped (Y6 and BTPOT-F) and linear (ITIC-4F) molecules, through density functional theory coupled with machine learning. Fields aligned with the molecular long axis induce stronger fluctuations than those along the short axis or out-of-plane directions of reorganization energy (λ_int) and transfer integral (V), with nonmonotonic variations due to charge redistribution and altered orbital interactions. Y-series NFAs, especially Y6, exhibit superior resilience, with symmetric architectures yielding more stable λ_int, V, and charge mobility than asymmetric or linear analogues. Remarkably, the charge transfer rate is accurately predicted using an extra trees model taking only two chemically meaningful descriptors, capturing molecular conformation and aggregation effects, as well as polarizability. The model further demonstrates strong transferability to unseen NFAs. This work explores the molecular-level factors governing field-modulated charge transport in complex NFAs and demonstrates accurate prediction of transport behavior, offering chemical design principles for next-generation high-mobility and field-stable OPV materials.