Direct Current Nanogenerator Based on Tribovoltaic Effect at WS2 Semiconductor Interface

With the fast development of microelectronic devices and the Internet of Things, triboelectric nanogenerators (TENGs) have been widely explored in self-powered micro/nano electronic devices recently. However, there are still many limitations for direct current (DC) TENGs. This study developed a semiconductor DC tribovoltaic nanogenerator (SDC-TVNG) based on n-type WS2 and p-type silicon (p-Si). Unlike alternating current output in contact-separation mode, the current generated during horizontal sliding friction, regardless of the sliding direction and whether it was positive or negative, was a DC signal from p-Si to n-type WS2. We studied the influence of frictional characteristics on the electrical output and found that the normal pressure and motion frequency had a positive correlation with the size of the DC signal. The maximum short-circuit current was 0.01 μA at a frequency of 1 Hz and a normal pressure of 10 N. The SDC-TVNG achieved a maximum power density of 2.46 μW/m2 at an outer impedance of 40 MΩ. Particularly, the tribovoltaic effect at the semiconductor–liquid–semiconductor interface was explored. Since the filled liquid layer could eliminate the insufficiency and uncertainty of the semiconductor–semiconductor contact friction, the maximum DC output of the semiconductor–liquid–semiconductor DC tribovoltaic nanogenerator (SLSDC-TVNG) was increased to 4.2 μA by a factor of 142 as compared to the current of 0.03 μA without adding the liquid (100 g/L NaCl solution) layer. The maximum power density of the device was 5.09 μW/m2 with a DC of 0.02 μA when the external resistance was 40 MΩ. This increased tribovoltaic nanogenerator with surface states at semiconductor interfaces, a composite system coupled by the liquid-enhancement effect and the tribovoltaic effect, promotes the separation of electron–hole pairs and the enhancement of current output.