Bifacial Structures of ZnS Humidity Sensor and Cd-Free CIGS Photovoltaic Cell as a Self-Powered Device

In this letter, a ZnS humidity sensor was integrated with MgF 2 /ZnS/CuIn 1-x Ga x Se 2 (CIGS)/Mo photovoltaic cell as a self-powered device. Both the ZnS layers of this bifacial device were deposited at the same time by a one-step process. This ZnS layer not only serves as the buffer layer of the CIGS photovoltaic cell on the upside, but is also used as the humidity sensing material on the backside. Under 1-sun illumination, the humidity current increased monotonically from 0.045 to 12.63 nA as we increased the related humidity (RH) from 30% to 95%. At RH 95%, the humidity current decreased from 13.1 to 4.93 nA while the illumination decreased from 1 to 0.1 sun. These results indicate that this device is of practical use as a self-powered humidity sensor.