Electrical and Ammonia Gas Sensing Properties of PQT-12/CdSe Quantum Dots Composite-Based Organic Thin Film Transistors

Abstract

The electrical and ammonia gas sensing properties of poly (3, 3”’-dialkylquaterthiophene) (i.e., PQT-12) and CdSe quantum dots (QDs) composite-based back-gated organic thin film transistors (OTFTs) fabricated on SiO2 coated heavily doped p-Si substrates by solution method have been investigated in this paper. The properties of pristine PQT-12 and PQT-12/CdSe QDs composite films have been investigated by transmission electron microscopy and atomic force microscopy. To investigate the effect of colloidal CdSe QDs on the characteristics of PQT-12-based OTFTs, the performance of pristine PQT-12-based OTFT has been compared with that of the PQT-12/CdSe QDs composite-based OTFT. The field effect mobility, threshold voltage, on/off current ratio, and subthreshold swing of the PQT-12/CdSe QDs composite-based OTFT are $4.2\times 10^{-3}$ cm2/Vs, −14.4 V, $1.9\times 10^{3}$ , and 5.2 V/dec while the corresponding values for pristine PQT-12-based OTFT are $1.4\times 10^{-3}$ cm2/Vs, −22.1 V, $3.6\times 10^{2}$ , and 7.9 V/dec, respectively. When the devices are exposed to ammonia gas, an estimated gas response of ~51% is obtained for PQT-12/CdSe QDs composite-based OTFT whereas the gas response of ~41% is achieved for the pristine PQT-12 OTFT sensor. The improved gas response in the PQT-12/CdSe QDs composite-based OTFT is attributed to enhanced charge transfer due to the CdSe QDs as compared with the pristine PQT-12-based OTFT.