Balancing the p- and n-type conductivities of the ZnO/graft-poly(3-hexylthiophene) copolymer nanocomposite to achieve sub-ppb NO2 detection in chemiresistive sensors at room temperature

Hybrid organic/inorganic composites are a frequent material used in chemoresistive sensors. These composites typically contain components that exhibit p- and n-type electrical conductivity, so as to enable the formation of p–n junctions and increase the sensitivity of the sensors. The specific mechanism behind the operation of such junctions appears to be well-understood and is rarely examined on a case-by-case basis. The interactions between p- and n-type conductors, however, need not be beneficial to the performance of the sensor. In this work, we provide evidence of the competition between p- and n-type conductivities of a hybrid nanocomposite activated by UV light, subjected to ageing and provide a mechanistic description of the underlying processes, as well as indicate potential for such phenomena to be harnessed in development of future sensor generations. By using nanocomposite consist of nanostructured ZnO and poly(3-hexylthiophene) based graft-comb-copolymers we obtained sensor material that can achieve sub-ppb detection limit of NO₂ (as low as 50 ppt) capabilities at room temperature. It is experimentally demonstrated that proper choice of polymer material used in the nanocomposite provide stabilisation of baseline drift and lowers limit of the detection while ensuring good adhesion of the receptor layer to the substrate.