Tuning of interfacial charge transport in polyporphine/phthalocyanine heterojunctions by molecular geometry control for an efficient gas sensor.

[Display omitted] • Zinc porphine is electropolymerized into two structural forms (pZnP-1 & pZnP-2) • Monomers are orthogonally linked in pZnP-1 while ZnP rings are fused in 2D in pZnP-2. • pZnP-1 shows low conductivity while pZnP-2 displays high conductivity. • pZnP-1/LuPc 2 device shows interfacial charge transport contrary to bulk transport in pZnP-2/LuPc 2. • Heterojunction sensor based on pZnP-1 detects NH 3 gas below environmental guidelines. Owing to high interfacial conductivity, organic heterostructures hold great promises to augment the electrical performances of electronic devices. In this endeavor, the present work reports fabrication of novel polyporphine/phthalocyanine heterostructures and investigates the modulation of charge transport induced by structural change of polyporphine and its implication on ammonia sensing properties. Polyporphines materials are electrosynthesized by oxidation of zinc(II) porphine monomer that corresponds to the fully unsubstituted porphyrin. At less-positive anodic potential, low conducting meso , meso -singly-linked type-1 polymer (pZnP-1) is formed in which a monomer unit stays orthogonal to its neighbors. At higher anodic potential, monomer units are fused in the 2D plane to produce β , β - meso - meso - β , β -triply-fused type-2 polymer (pZnP-2), having a π-conjugated structure and high conductivity. Association of these polymers in organic heterojunction devices with lutetium bis-phthalocyanine (LuPc 2) reveals non-linear current–voltage (I-V) characteristics typical for interfacial accumulation of charges in the heterostructure for pZnP-1 and a linear I-V behavior for pZnP-2. Characterization of these heterojunctions by impedance spectroscopy further confirms the predominance of interfacial charge transport in pZnP-1/LuPc 2 which is improved with increasing bias, while largely bulk charge transport independent of bias prevails in pZnP-2/LuPc 2 device. Different regimes of charge transport influence ammonia-sensing properties of the devices, such that pZnP-1/LuPc 2 demonstrates highly sensitive, reversible and stable response, while pZnP-2/LuPc 2 shows low and unstable response. [ABSTRACT FROM AUTHOR]