Thermally evaporated indium-free, transparent, flexible SnO2/AgPdCu/SnO2 electrodes for flexible and transparent thin film heaters

We investigated the characteristics of themally evaporated SnO2/Ag-Pd-Cu (APC)/SnO2 multilayer films for applications as damage-free, indium-free, flexible, and transparent electrodes for high performance flexible and transparent thin film heaters (TFHs). The top and bottom SnO2 layers and APC interlayer were prepared by a multi-source evaporation process, and the effect of the thickness of each layer on the resistivity, optical transmittance, and mechanical flexibility of the SnO2/APC/SnO2 electrodes was investigated in detail. Based on a figure of merit value, we obtained a SnO2/APC/SnO2 electrode with a low sheet resistance of 9.42 Ohm/square and a high optical transmittance of 91.14%. In addition, we examined the mechanical properties of the SnO2/APC/SnO2 electrode using various bending tests such as inner bending, outer bending, dynamic fatigue, and a twisting test. By comparing the crack shape of the SnO2/APC/SnO2 electrode bent beyond the critical bending radius (2~3 mm), we suggest a possible crack formation mechanism for the SnO2/APC/SnO2 electrodes. Furthermore, we evaluated the feasibility of the SnO2/APC/SnO2 electrodes for flexible and transparent TFHs. By correlating the sheet resistance of the SnO2/APC/SnO2 electrode and the performance of TFHs, we show the importance of transparent electrodes for high performance flexible and transparent TFHs.