Investigation of humidity effects on electrical properties of PTB7-Th and PCBM sensor

Abstract

This paper reports the fabrication of semitransparent semisurface-type samples of an indium tin oxide (ITO)/poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b 0] dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl}: (PTB7-Th):[6,6]-Phenyl C61 butyric acid methyl ester (PCBM)/graphene composite humidity sensor. The transparency of the sensor was 58–60%. The dependences of the resistance, impedance and capacitance at 100 Hz, 1 kHz, 10 kHz, 100 kHz and 200 kHz of the ITO/PTB7-Th:PCBM/graphene composite samples on relative humidity in the range 50–93% were investigated. It was observed that as humidity increased from 50 to 93%, the resistance and impedances (at 1 kHz) of the samples decreased on average by factors of 7·48 and 58·75, respectively. Under the same experimental conditions (1 kHz), the capacitances of the samples increased by a factor of 42. As the frequency was increased from 100 Hz to 200 kHz, the impedance decreased by factors of 20 and 7 at relative humidity values of 50 and 62%, respectively. The corresponding capacitance decreased by factors of 33 and 178, respectively. The semitransparent PTB7- and -PCBM-based humidity sensors can be used for measurement of humidity, as well as a teaching aid where control of illumination or light intensity is desirable.