Advanced functional thin films for energy conversion and storage devices deposited by plasma-based processes

Energy conversion and storage devices are essential to reach sustainability and CO2 emission reduction. Solar cells, fuel and electrolysis cells, batteries and supercapacitors are under a stringent development that requires functional materials and interfaces with tunable properties that can provide the needed device performance. The multilayered structure, involving electrodes, electrolytes, absorbers, mixed or charge dependent conductors are shrinking in size and sometimes evolve from 2D to 3D architectures. [1] Within this development, to the classic methods for materials synthesis (sintering, doctor blade, tape casting and ball milling) plasma based or assisted technologies such as sputtering, chemical vapor deposition, atomic layer deposition or thermal spray started to contribute as well. In this context, this work provides an overview on current and potential use of plasma technologies for functional thin films for energy conversion and storge device with focus on solar cells, fuel cells and micro batteries. Special attention is dedicated to metal oxides by magnetron sputtering where the role of energetic oxygen-negative-ions is corelated with plasma and thin film properties as well as with the growth mechanism. A dual thermal-electrostatic probe used to measure plasma density, electron temperature and plasma potential, revealed that the best conditions to deposit metal oxides, under growth assistance of low-energy oxygen negative ions, corresponds to the transition from a plume-like discharge to magnetron. Analytical characterization using TOF-SIMS and 2D-XRD demonstrated that preferential sputtering can play a significant role for binary metal oxides with significant differences in sputtering yield as for aluminum doped zinc oxide. [3]