Volatile Imide Additives with Large Dipole and Special Film Formation Kinetics Enable High-Performance Organic Solar Cells

Large dipole moment additives have strong interactions with the host materials, which can optimize morphology and improve the photovoltaic performance of organic solar cells (OSCs). However, these additives are difficult to remove due to their strong intermolecular interactions, which may impair stability. Developing volatile additives with large dipole moments is challenging. Herein, we first report volatile imide additives that could effectively improve the performance of OSCs through morphology modification. Three additives N-(o-chlorophenyl)phthalimide (oClPA), N-(m-chlorophenyl)phthalimide (mClPA), and N-(p-chlorophenyl)phthalimide (pClPA) were screened to investigate the effort of positional isomerization on molecular configuration and interaction. These additives (ClPAs) have larger dipole moments (2.0664 Debye for oClPA, 4.2361 Debye for mClPA, and 4.7896 Debye for pClPA) compared to reported solid additives. In contrast to traditional simultaneous nucleation and crystal growth, ClPAs could induce the acceptor to nucleate first and then grow, which contributes to forming high-quality acceptor domains with better crystallinity. To our knowledge, this unique film formation kinetics was reported first. The power conversion efficiency (PCE) of OSCs based on PM6:BTP-eC9 treated with pClPA was improved from 16.13 % to 18.58 %. Additive pClPA also performed well in PM6:L8-BO, PM6:Y6, and D18:L8-BO systems, and a high PCE of 19.04 % was achieved. Our results indicate using imide unit to construct solid additives is a simple and effective strategy, and the positional isomerization of halogen atom also has a large effect on the photovoltaic performance.