Combinatorial detection of volatile organic compounds using metal-phthalocyanine field effect transistors

We apply percolation theory to explain the operation of multiple-use gas sensors based on organic field effect transistors (OFETs). For reversible operation, we predict that energetic disorder in the channel can obscure interactions with the analyte, because chemically induced traps are overwhelmed by the natural disorder. Consequently, the sensitivity of an energetically disordered OFET-based chemical sensor is significantly inferior to the ideal disorder-free case. Current modulation in disordered OFETs is predicted to rely on morphological alteration of percolation paths. The theory is compared to results from an array of metal phthalocyanine (MPC) transistors exposed to low concentrations of solvents. Despite the presence of very large adsorption fractions of solvent on the channel, the current modulation is small, consistent with theory. Chemical selectivity is possible, however, because the central metal atom of the MPC determines the strength of the solvent-MPC interaction, which in turn determines the amount of solvent adsorbed on the OFET channel. This work suggests that OFET-based sensors may be better suited to applications where the analyte binding energy exceeds the intrinsic energetic disorder of the organic semiconductor.