Morphology Inversion of a Non-Fullerene Acceptor Via Adhesion Controlled Decal-Coating for Efficient Conversion and Detection in Organic Electronics

In this study, a promising film formation technique is highlighted, named mold-assisted decal-coating, as a thin film transfer printing process using the polyurethane acrylate-based stamping mold. By optimizing the surface energy of the mold with wetting coefficient theory, the mold-assisted decal-coating process is successfully demonstrated by transferring the photoactive layer composed of the polymer donor, poly4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] and a narrow bandgap non-fullerene acceptor (NFA), 2,2′-4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno1,2-b:5,6-b′]dithiophene-2,7-diyl]bis4-(2-ethylhexyl)oxy]-5,2-thiophenediyl]methylidyne(5,6-difluoro-3-oxo-1H-indene-2,1(3H)-diylidene)]]bispropanedinitrile]. This process induces a well-ordered morphology of photoactive material, prevents damage to the underlying layer by suppressing the solvent penetration. Both photovoltaic cells and photodetectors prepared by the decal-coated photoactive layers containing fluorinated NFAs showed higher performance (power conversion efficiency = 10.69% and specific detectivity = 1.27 × 10¹² A cm Hz^1/2 W⁻¹, respectively) than those of cells prepared by the spin-coating method owing to morphology inversion and smoother interface that led to suppressed internal resistance and enhanced charge flow in normal structure. Thus, the reproducible decal-coating process using a customized elastomeric mediator is an important thin film coating technique for efficient next-generation organic optoelectronic materials.