Hierarchical spindle structures of Li+-doped ZnO for a high performance humidity sensor

Abstract

In this paper, controllable composites of Li⁺-doped ZnO with hierarchical spindle structures have been successfully prepared on conductive glass via a simple hydrothermal synthesis. By introducing Li⁺, a cation with strong adsorption capacity, the humidity sensing performance of the hierarchical spindle has been greatly improved and has become controllable. Compared with ZnO, the composite of Li⁺-doped ZnO keeps the hierarchical spindle structure of the material, improves the adsorption speed and reduces the response time. When the relative humidity (RH) varies from 11% to 95%, the impedance of the Li⁺-doped ZnO composite changes by 3 orders of magnitude, and its response and recovery time are 14 s and 11 s, respectively. By analyzing the sensing mechanism of the sensor, the effect of Li⁺ doping has been discussed. Under a low humidity condition, as an adsorption active material, Li⁺ improves the hydrophilic ability of the sensor. In a high humidity environment, Li⁺ participates in the conduction process resulting in a sharp drop in resistance, and the humidity sensing performance of the sensor has been improved. Because of the fast response time of Li⁺-doped ZnO, it has a crucial significance in the development prospects for humidity sensors and provides new insights for humidity sensors based on ZnO.