The Ultimate Guide to Creating TiO2 Pinholes with Dust Particles

Buabthong, P., Ifkovits, Z. P., Kempler, P. A., Chen, Y., Nunez, P. D., Brunschwig, B. S., Papadantonakis, K. M., and Lewis, Nathan S., "Failure modes of protection layers produced by atomic layer deposition of amorphous TiO 2 on GaAs anodes." Energy & Environmental Science, (2020), 13, 4269-4279. DOI: 10.1039/D0EE02032J

tl;dr

• We put solar cells in highly corrosive water to make hydrogen from sunlight.
• It dissolves pretty quickly, so we coat it with TiO₂ films. Still dissolve 🙄, people think there is probably a bunch of dust on the solar cell when you coat it, so you have these "pinholes" on the film after you're done.
• This paper: we confirmed it started to dissolve from these small pinholes. Look like dust, behave like dust, probably dust.
• So we clean the room really well -> no dust -> no longer dissolve in the first minute
• The ones with no pinholes still fail at some point, need more investigation.

Comments

• Being professional and scientific, we are not allowed to simply call these "pinholes," but rather "physical defects." Guess what everyone refers to these things in my lab... pinholes. There's a trade-off here between using accurate language for academic preciseness and writing for the purpose of communicating the ideas to our colleagues. Unfortunately, the former buries most of our work deep in the pile of academic publications.
• We still didn't observe the dust particles directly, but merely their mask left in the film. If we can quantify the nature of these dust, it's likely we'll be able to develop a scheme to remove them prior or during the deposition.
• Alright, you can't help it; you don't have access to our magic ALD recipe or Caltech's cleanroom, so you have a few pinholes. The next step is to find a way to plug or passivate these holes. I think this work is even more important than figuring out how to grow the film without any holes. (you can potentially use it in the semiconductor industry)