Effect of the receptor layer on the response selectivity, response reversibility and reproducibility. (a) Mean response of the sensor groups with different receptor layers: TiO-, Cu-, Zn-TPP and sensors without receptor layer towards 100 ppb of NO2 in humid air with 95% RH. (b) Response curves to NO2 at 95% for the non-modified OFET sensor and the devices with TiO-, Cu- and Zn-TPP receptor layers demonstrating their effect on the response selectivity. Mean values are presented with their standard errors. (c) Response-time (left axis) dependence for 6 non-modified OFET sensors of the array on a single substrate for 2 successive experiments in humid air at 95% RH (color lines) and its mean value (bold blue line) with NO2 pulses from 100 to 1000 ppb shown in light blue.