Cadmium selenide quantum dots: Synthesis, characterization and their humidity and temperature sensing properties with poly-(dioctylfluorene)

[Display omitted] •Successful synthesis of CdSe QDs (∼4 nm) by using aqueous colloidal route method.•Fabrication of Ag/F8-CdSe QDs/Ag multipurpose sensors by using spin coating method.•Enhanced, stable and linear response of the sensor to humidity and temperature variations.•Broad range of humidity and temperature sensing, faster response and recovery times due to high surface area of CdSe QDs.•Well-reproducible and reversible results with small hysteresis. In this paper, we report synthesis, thin film characteristics and sensing properties of cadmium selenide (CdSe) quantum dots (QDs) for enhancing the humidity and temperature sensing of a polymeric semiconductor poly-(9,9-di-n-octylfluorenyl-2,7-diyl) (F8). Transmission electron microscopy (TEM) has been performed to study the texture, distribution over surface and size of the synthesized CdSe QDs. TEM image revealed slightly non-uniform distribution of the QDs with an average size of 4 nm having three-dimensional quantum confinement features. Atomic force microscopy (AFM) is carried out to investigate the average grain size and surface roughness of the F8-CdSe nanocomposite film. To understand the role of CdSe QDs on the sensing properties of F8, a blend F8-CdSe QDs has been prepared at 10:1 wt-percent (wt%) of F8 and CdSe QDs, respectively, in chloroform. An Ag/F8-CdSe QDs/Ag surface-type sensor has been fabricated via spin coating F8-CdSe QDs nanocomposite on a 45 μm gap between the pre-patterned silver (Ag) electrodes on glass substrate. The fabricated Ag/F8-CdSe QDs/Ag sensor has been studied for humidity and temperature sensing by measuring capacitance (C) of the sensor as a function of humidity and temperature, respectively. The Ag/F8-CdSe QDs/Ag sensor exhibits enhancement in the sensing parameters such as response time and recovery time i.e., 9 s and 7 s, respectively, as compared to our previously studied Ag/F8/Ag sensor whose response and recovery time were 15 s and 7 s, respectively. This improvement is due to the addition of CdSe QDs in F8 polymer matrix which changes some of the important properties of the F8-CdSe QDs nanocomposite such as electron polarizability, polarity, hydrophobicity and size dependent properties. The role of porosity (P) in the sensing properties of the active film of Ag/F8-CdSe QDs/Ag device has also been explored. The Ag/F8-CdSe QDs/Ag based sensor shows approximately linear change in C as a function of humidity and temperature with wide range of sensitivity from 25