Effect of hydrogen addition on bulk properties of sputtered indium tin oxide thin films

In this work indium tin oxide (ITO) was deposited at low temperature using DC magnetron sputtering under the addition of hydrogen gas. Optical and electrical film properties were studied as a function of deposition and subsequent annealing parameters. A strong correlation between the bulk properties and the ITO film morphology could be observed. Post-deposition annealing of the 100 nm thick ITO layers was performed in ambient air at temperatures between 200°C and 600°C. This covers the relevant temperature range applied for the metallization of amorphous silicon based heterojunction solar cells (∼200°C) but also for post-deposition treatments at elevated temperatures, favoured for the poly-Si based passivating contact technology (TOPCon). The addition of hydrogen to the sputtering gas mixture considerably affected the opto-electronic properties of the amorphous ITO films in the pre-annealed state, mainly by increasing the charge carrier density. Furthermore the crystallization process was influenced positively, being reflected in larger crystallites leading to higher electron mobility in poly-crystalline ITO.