Given the great potential for achieving record breaking
organic
solar cells (OSCs), newly explored solid additives that could optimize
nanoscale morphology of active layers have rapidly gained widespread
attention. Herein, a new volatile solid additive 2,5-dichlorothieno[3,2-b]thiophene (TT-Cl) is delicately explored, fully satisfying
the design criteria of a planar conjugated skeleton with suitable
molecular size, symmetrical geometry, and proper halogenation. When
applied in the state-of-the-art OSCs with diverse active layers, the
quite high crystallinity of TT-Cl and strong interactions with light-harvesting
components lead to optimized molecular crystalline ordering, fibrillar
networks, and vertical phase distributions, thus offering a significant
performance enhancement. Consequently, PM6:Y6-based binary and ternary
OSCs achieved PCEs of 18.20% and 18.95%, respectively. Moreover, PM6:CH23-based
binary OSCs presented an outstanding PCE of 18.72%. Our work not only
provides a broad-spectrum solid additive to optimize film morphologies
powerfully but also manifests great potential for achieving a record-breaking
PCE of OSCs.