Bilayer Heterojunctions of Phthalocyanines and Conjugated Microporous Porphyrin Polymers for High-Performance Ammonia Sensing

This study presents the fabrication and characterization of bilayer heterojunction (BLH) ammonia sensors combining copper(II) fluorophthalocyanine (CuF8Pc and CuF16Pc) sublayers with a microporous conjugated polymer of poly[nickel(II) 5,10,15,20-tetra(3-thienyl)porphyrin] (pNiTTP) synthesized via oxidative chemical vapor deposition (oCVD). The oCVD process enables direct gas-phase oxidative coupling of metalloporphyrins, yielding uniform, thickness-controlled polymer thin films with a high degree of π-conjugation and an intrinsic microporosity exceeding 100 m2 g−1. Structural, optical, and electrical analyses confirmed well-defined BLH architectures and interfacial charge transport. Ammonia sensing tests across 1−90 ppm and 30−70% RH revealed complementary behaviors: CuF8Pc/pNiTTP exhibited p-type response and higher sensitivity at elevated NH3 concentrations and humidity, while CuF16Pc/pNiTTP displayed an n-type polarity and superior performance at low concentrations under dry conditions. At 45% RH, sensitivities reached −0.57% and 0.90% ppm−1, with detection limits of 350 and 270 ppb, respectively. Advanced kinetic analysis indicated a single dominant process for CuF16Pc/pNiTTP with a rapid response time (t90 ≈ 1 min), outperforming CuF8Pc/pNiTTP (t90 ≈ 7 min). These findings demonstrate that microporous conjugated porphyrin polymers enable humidity-tunable sensitivity, fast kinetics, and low detection limits, while the proposed kinetic framework offers a robust tool for comparing dynamic behaviors across sensor platforms.