Thermally evaporated amorphous InZnO thin film applicable to transparent conducting oxide for solar cells

In recent years, amorphous InZnO (a-IZO) film gets recognition for the possibility as a transparent conducting oxide (TCO) layer with outstanding its optical and electrical properties in photovoltaic devices. Generally, the sputtering technique is normally used to deposit a-IZO film, which suffers from plasma damage exerting a negative influence on device performance. Here, we suggest an alternative to deposit a-IZO film with a thermal evaporation technique using a simply customized system to compensate defects by plasma damage. Thermally grown IZO films by controlling two variables of Zn rate and substrate temperature show the distinguishable characters in terms of transparency, conductivity and crystalline structure with a substantial change of Zn content in In_1-xZn_xO. Zn incorporation in IZO film is considered as a critical key to determining the crystal structure and IZO film quality. In the thermal evaporation system, phase transition occurs from crystalline to amorphous; the IZO film indicates the superior property in the amorphous phase than crystalline structure. We acquired the optimized IZO film with amorphous phase in the relative concentration of In_0.73Zn_0.27O grown at 200 °C. To demonstrate the feasibility of a-IZO film as a TCO layer, Cu(In,Ga)Se₂ solar cell was practically fabricated, which shows excellent performance. It is attributed to the absence of plasma damage during deposition of the a-IZO film, proved by the decrease of shunt resistance in the solar cell.