Given the great potential for achieving record breakingorganicsolar cells (OSCs), newly explored solid additives that could optimizenanoscale morphology of active layers have rapidly gained widespreadattention. Herein, a new volatile solid additive 2,5-dichlorothieno[3,2-b]thiophene (TT-Cl) is delicately explored, fully satisfyingthe design criteria of a planar conjugated skeleton with suitablemolecular size, symmetrical geometry, and proper halogenation. Whenapplied in the state-of-the-art OSCs with diverse active layers, thequite high crystallinity of TT-Cl and strong interactions with light-harvestingcomponents lead to optimized molecular crystalline ordering, fibrillarnetworks, and vertical phase distributions, thus offering a significantperformance enhancement. Consequently, PM6:Y6-based binary and ternaryOSCs achieved PCEs of 18.20% and 18.95%, respectively. Moreover, PM6:CH23-basedbinary OSCs presented an outstanding PCE of 18.72%. Our work not onlyprovides a broad-spectrum solid additive to optimize film morphologiespowerfully but also manifests great potential for achieving a record-breakingPCE of OSCs.