Improving Carrier Mobilities in Soft Sputtered ITO Coatings Made by Hollow Cathode Sputtering
Tuesday, May 9, 2023
2:30 PM - 4:30 PM

Zachary Leuty, Mark George, Zhengshan Yu, Zachary Holman, Arizona State University, Tempe, AZ DC Magnetron sputtering is widely used in various industries to deposit transparent conductive oxide (TCO) coatings due to their excellent coating conductivity, transparency, and high areal throughput rates. However, high-power manufacturing sputtering conditions can cause irreversible ion damage to sensitive devices like silicon heterojunction and perovskite solar cells, resulting in lower power conversion efficiencies. Buffer layers and slower, gentler sputtering methods (like RF sputtering) are often used in R&D to avoid sputtering damage, but these add considerable cost and complexity when scaling emerging solar cell technologies. Hollow cathode gas-flow sputtering is a promising technique to solve these challenges with its manufacturing-relevant deposition rate, low-cost rough vacuum operation, and low bulk resistivity TCO coatings. However, in the literature, low bulk resistivity TCO values are reported using substrate temperatures over 300°C, which is not compatible with the thermal budget for sputtering-sensitive applications such as silicon heterojunction or perovskite solar cells. The hollow cathode geometry suppresses sputtering damage by directing high-energy recoiled neutral Argon atoms from one target towards the other instead of impacting the substrate and suppresses these energetic species with the short mean-free-path in the 0.1 – 1 Torr operating pressure range. However, these conditions give insufficient adatom energy, resulting in lower density coatings with bulk resistivity values orders of magnitude higher than the state-of-the-art. In this work, we explore how changing the anode location can direct electrons and low-energy ions toward the substrate to improve crystalline growth of the TCO coatings and increase the carrier mobility in ITO coatings. With a clever anode design, carrier mobilities over 30 cm2/V·s and bulk resistivities of 5 ⨯ 10-3 ohm-cm can be achieved with a dynamic deposition rate greater than 20 nm·m/min for a 0.125 m long cathode. This work highlights the potential to improve the performance and reduce the cost of TCO coatings deposited using hollow cathode gas-flow sputtering, offering a promising solution for manufacturing high-efficiency and low-cost solar cells.

Zach Leuty - Arizona State University