Low temperature plasma chemical vapor deposition (PCVD) of fluorinated tin-oxide transparent conducting oxide

Transparent conducting oxide (TCO) thin film is one of the key components in photovoltaic and display devices. Indium tin oxide (ITO) is the best known TCO material; however, its cost is high. Fluorinated tin oxide is one candidate to replace ITO as a TCO material. It is stable at high temperature, economical to produce and more benign compared to other TCO materials. The bulk resistivity of tin oxide deposited with conventional methods (PECVD, spray pyrolysis and atmospheric pressure CVD) reach as low as 5 × 10^-4 Ohm-cm. However, the deposition temperature is typically above 350°C and not suitable for temperature sensitive processes such as CIGS, CdTe, a-Si and quantum dot based solar cells or large area plastic substrates. We have developed plasma CVD (PCVD) process to deposit fluorinated tin oxide at low temperature (< 250°C). The fluorinated tin oxide bulk resistivity deposited at 250°C and 200°C are 9.0 × 10^-4 Ohm-cm and 1.2 × 10^-3 Ohm-cm respectively. The film transmittance at a 10 Ohm/sq sheet resistance is greater than 94% at 500 nm. In this presentation, we will discuss correlations between electrical properties and microstructure as well as stability of the deposited films. We will also discuss the economical impact of PCVD fluorinated tin oxide films compared to other TCO materials.