Junction-free silver network electrode : from potential applications to degradation

Abstract

Transparent conducting electrodes (TCEs) are one of the essential components of devices such as solar cells, and the capacitor touch sensors of smartphones. With increasing demand for these devices, the research on transparent conducting electrodes becomes a very popular topic. In this thesis TCEs are fabricated by the method of cracked template polymer and different network densities are obtained by varying the spin coating speed of the templated polymer. The degradation of silver network electrodes with high transparency (82%) and low sheet resistance 8Ω/□ is studied by using thermoreflectance and scanning electron microscopy (SEM). Thermoreflectance (TR) results show that the existence of hot spots contributes to faster breaking down of silver network electrodes. Further study on SEM images reveals the increase in grain size after constant voltage bias which is an electromigration related phenomena. The results of finite element simulation precisely pinpoint the hot spots on each network, confirming the accuracy of TR result. Finite element simulation allows us to study the current density on each silver wire within the network, showing a relatively high current density on horizontal wires than vertical wires. It suggests that the number of horizontal wires is key to increase the lifetime of silver network electrode by decreasing the current density. Potential applications of the silver network electrode such as heaters, pressure sensors, and acoustic sensors are studied. Transparent flexible heaters are successfully fabricated which can be used on thermotherapy and as a container temperature controller. This heater can heat up to 75 ̊C by applying a voltage of 5V within 10s. Transparent acoustic sensors are also fabricated by using silver network as a transparent membrane which shows a signal to noise level 23.7dB. This sensor is operational and transparent. Our transparent pressure sensor can sense a pressure change as low as 1.1Pa.