Analyte selective response in solution-deposited tetrabenzoporphyrin thin-film field-effect transistor sensors

Organic thin film transistor (OTFT) chemical sensors rely on the specific electronic structure of the organic semiconductor (OSC) film for determining sensor stability and response to analytes. The delocalized electronic structure is influenced not only by the OSC molecular structure, but also the solid state packing and film morphology. Phthalocyanine (H2Pc) and tetrabenzoporphyrin (H2TBP) have similar molecular structures but different film microstructures when H2Pc is vacuum deposited and H2TBP is solution deposited. The difference in electronic structures is evidenced by the different mobilities of H2TBP and H2Pc OTFTs. H2Pc has a maximum mobility of 8.6 × 10−4 cm2 V−1 s−1 when the substrate is held at 250 °C during deposition and a mobility of 4.8 × 10−5 cm2 V−1 s−1 when the substrate is held at 25 °C during deposition. Solution deposited H2TBP films have a mobility of 5.3 × 10−3 cm2 V−1 s−1, which is consistent with better long-range order and intermolecular coupling within the H2TBP films compared to the H2Pc films. Solution deposited H2TBP also exhibits a textured film morphology with large grains and an RMS roughness 3–5 times larger than H2Pc films with similar thicknesses. Despite these differences, OTFT sensors fabricated from H2TBP and H2Pc exhibit nearly identical analyte sensitivity and analyte response kinetics. The results suggest that while the interactions between molecules in the solid state determine conductivity, localized interactions between the analyte and the molecular binding site dominate analyte binding and determine sensor response.