Preparation of TiO2 and ZnO dispersions for inkjet printing of flexible sensing devices

Research presented in this article focuses on the preparation of functional dispersions for inkjet printing of nanoparticles as sensitive layers. The stable suspensions of MOx (M = Ti, Zn) were prepared using gum arabic (GA) and Solsperse (R) 40000 (SO) as dispersants. A special attention was paid to the monitoring of particle size evolution during the planetary ball milling of dispersions, so that optimum ratio between milling time and particle size can be determined. After adjusting the printing parameters, prepared inks were printed on the flexible PET substrate with interdigitated electrodes (IDE). Films printed with TiO2 ink stabilized by GA exhibited highly cracked surface which resulted in low current values, whereas ZnO ink stabilized by SO yielded crack-free surface and much higher current values. All investigated samples showed linear current behaviour in the range from -5 to 5 V indicating formation of ohmic contacts between electrodes and nanoparticles, but ZnO ink produced the highest current values. Gas sensing properties, tested at room temperature at several humidity levels and for different types of alcohols, revealed that printed sensor exhibits modest sensitivity for low humidity levels and slightly higher affinity towards methanol gas. Photo sensitivity measurement showed very high photocurrent values with strong potential for optoelectronic applications.