Probing the Architecture of Organic Heterojunctions Based on Zn(Salen)-Type/Lu(Bis-phthalocyanine) Complexes and Their Potential Application as Gas Sensors

Organic semiconductor devices based on planar (PHJ) and bulk (BHJ) heterojunctions have attracted considerable interest in recent decades. This work reports the preparation and characterization of heterojunctions based on a Zn(salen)-type complex (ZnL) and lutetium bis-phthalocyanine (LuPc2), either as ZnL/LuPc2 bilayers or ZnL:LuPc2 mixed films deposited on indium tin oxide interdigitated electrodes. Morphological, optical, and electrical properties were investigated by AFM, PeakForce TUNA nanoconductivity mapping, Raman and UV–vis spectroscopy, as well as current–voltage and impedance measurements. Bilayer films exhibited a uniform rough surface, whereas mixed films showed pillar-like or alveolar structures. Raman and AFM analyses revealed homogeneous mixed films containing distinct ZnL and LuPc2 domains. PeakForce TUNA demonstrated that the pillar-like features correspond to highly conductive LuPc2 domains dispersed within a less conductive ZnL matrix, evidencing heterogeneous conductive pathways at the nanoscale. Thermal annealing induced significant changes in the optical and electrical properties of both bilayer and mixed films. The potential of these materials as conductometric ammonia sensors was also examined. At 90 ppm NH3, as-prepared mixed films showed a tenfold higher relative response (−40%) than bilayers (−4.1%). Annealing further enhanced sensor performance for both systems.