Step-by-step modulation of crystalline features and exciton kinetics for 19.2% efficiency ortho-xylene processed organic solar cells

Abstract

A novel fluoro-methoxylated end group for Y-series acceptors is produced, and asymmetric substitution strategy is applied as a step-by-step optimization.19.24% power conversion efficiency is achieved for industrially compatible solvent ortho-xylene processed organic solar cells.Underlying morphological and photo-physical variation is revealed for device performance difference brought by solvent selection, which could set up a template for future research on similar topics. With plenty of popular and effective ternary organic solar cells (OSCs) construction strategies proposed and applied, its power conversion efficiencies (PCEs) have come to a new level of over 19% in single-junction devices. However, previous studies are heavily based in chloroform (CF) leaving behind substantial knowledge deficiencies in understanding the influence of solvent choice when introducing a third component. Herein, we present a case where a newly designed asymmetric small molecular acceptor using fluoro-methoxylated end-group modification strategy, named BTP-BO-3FO with enlarged bandgap, brings different morphological evolution and performance improvement effect on host system PM6:BTP-eC9, processed by CF and ortho-xylene (o-XY). With detailed analyses supported by a series of experiments, the best PCE of 19.24% for green solvent-processed OSCs is found to be a fruit of finely tuned crystalline ordering and general aggregation motif, which furthermore nourishes a favorable charge generation and recombination behavior. Likewise, over 19% PCE can be achieved by replacing spin-coating with blade coating for active layer deposition. This work focuses on understanding the commonly met yet frequently ignored issues when building ternary blends to demonstrate cutting-edge device performance, hence, will be instructive to other ternary OSC works in the future.