ZnO/MoO3 Heterojunction Thick Films to Detect ppb Level Volatile Organic Compounds

The development of a fast, stable metal oxide-based VOC sensor for the detection of trace-level ppb concentrations, remains a challenge. Recently, many composite materials have been investigated to try and develop sensors with these characteristics. Here, we report on the development of ZnO/MoO
₃
heterojunction thick film devices, fabricated by a spin-coating technique, to detect a wide range of VOCs at application relevant ppb level concentrations. For comparison, pristine ZnO and pristine MoO
₃
devices were also fabricated. Sensors were tested at different temperatures and resulting in an optimum temperature of 380°C. The sensors were tested towards 11 different VOCs at ppb concentrations. Of all the sensors tested, the heterojunction device showed the highest response to VOCs, with the highest sensitivity towards 200 ppb of ethanol (R
_a
/R
_g
= 12.84). The results compared well with the pristine materials, with the response of the ZnO material being 6 times smaller and MoO
₃
10 times smaller compared to their heterojunction counterpart. The response times of the heterojunction device were also faster, at around 30 sec compared with 120 sec for pristine materials.