Surface tailored Ti-oxo clusters enabling highly efficient organic solar cells

In this work, the hierarchical surface reactivity of a kind of Ti-oxo cluster (TOC) with robust cyclic structure, CTOC, supported by multiple surface ligands, has been initially established. By this method, a series of aromatics (i.e., benzoate for CTOC-Ph, 4-methylbenzoate for CTOC-PhMe and 4-cyanobenzoate for CTOC-PhCN) substituted CTOC-Ars, with identical TOC core have been produced. These CTOC-Ars can be solution-processed into smooth films with order microstructures and optimized semiconducting properties, driven by intermolecular interactions of the aromatics. When using CTOC-Ph as cathode interlayer (CIL) in PM6:BO-4Cl based organic solar cells (OSCs), power conversion efficiencies (PCEs) up to 17.7 % have been achieved, much higher than 15.6 % of those with CTOC CIL. The distinct electron doping behavior with non-fullerene acceptor and higher adsorption energy with the polymer donor has been successfully unraveled, which can enable CTOC-Ph more intimate contact with the photoactive layer and facilitate more efficient charge transport. Moreover, the gen-erality of CTOC-Ars as CIL for efficient OSCs has been confirmed in varied OSC systems, in which high PCEs of 18.4 % can be provided for PM6:L8-BO system.