Langmuir–Blodgett Assembly of PM6 and N2200 Polymer Planar Heterojunctions for Interfacial Probing

Precise control over thin-film morphology and interfacial organization is essential for solution-processed organic electronics. We demonstrate the successful Langmuir-Blodgett (LB) fabrication of nanometer-precise, uniform PM6 and N2200 polymer films. Optimized solvent and spreading conditions yield controlled assembly of uniform and homogeneous mono- and multilayers. PM6 formed isotropic films with tangled coiled structures, while N2200 showed anisotropic domains with directional π-stacking and extended branch-like polymer chains. Nanomechanical analysis revealed a 35-40% increase in surface elasticity for multilayers versus monolayers. Surface potential measurements underlined a thickness-dependent transition from substrate-dominated electrostatics in monolayers to a bulk-like behavior in multilayers, while photoluminescence mapping confirms preservation of emissive functionality even down to a monolayer. Preliminary photoresponsivity tests with photoactive layers below 20 nm show a reproducible increase in short-circuit current density upon increasing the number of PM6 and N2200 layers from five to six each, as confirmed by measurements across multiple devices. This trend is attributed to an absorption cross section that scales with increasing layer thickness. Our results position the LB method as a robust platform for constructing ultrathin, structurally coherent, and electronically active polymer interfaces with nanometer-scale thickness control.