Manipulating Hierarchical Aggregation Structure via Film-forming Kinetics Enables Organic Photovoltaics over 20% Efficiency

Abstract

The non-equilibrium dynamics of solvent evaporation and polymer diffusion induce vertical crystallization differences in the donor film, which pose great challenges to the precise control of the ideal vertical phase morphology in pseudo-planar heterojunction (PPHJ) organic photovoltaics (OPVs). In this study, the Peclet number (Pe) was first proposed as a predictive parameter to evaluate the correlation between solvent evaporation and the vertical gradient distribution morphology of the active layer during the film-forming process. This further directs the regulation of the hierarchical aggregation structure and vertical crystallization behavior of the polymer donor, thereby inducing ordered donor/acceptor interpenetration and ultimately achieving the construction of active layers with controllable heterojunction architectures. Depth-dependent light absorption spectroscopy and in situ depth-dependent fluorescence intensity measurements confirmed that Pe is about 1 can induce vertical crystallization differences in various polymer donors to form a PPHJ active layer with an ideal vertical gradient distribution morphology. Consequently, the toluene-processed PPHJ device achieved competitive power conversion efficiencies of 20.07%/16.86% (0.04/16.94 cm²) via blade coating technology.